# Lakhmir Singh Class 10 Physics 2nd Chapter Magnetic Effect of Electric Current Solution

## Lakhmir Singh Class 10 Physics 2nd Chapter Magnetic Effect of Electric Current Solution

Lakhmir Singh Manjit Kaur Physics Solution: Magnetic Effect of Electric Current Chapter 2. Here you get easy Solutions of Lakhmir Singh Class 10 Physics Solution Chapter 2. Here we have given Chapter 2 all Solution of Class 10. Its help you to complete your homework.

• Board – CBSE
• Text Book – Physics
• Class – 10
• Chapter – 02

### Lakhmir Singh Class 10 Physics 2nd Chapter Solution

#### Magnetic Effect of Electric Current

Very Short Answer Type Questions :-

1) State any two properties of magnetic field lines.

Ans:

• Magnetic field lines always starts from north pole of the magnet and ends on the south pole of the magnet.
• And inside the magnet the direction of magnetic field lines is from South pole of magnet to the north pole of magnet.
• Hence magnetic field lines are closed curves.

2) What are the two ways in which you can trace the magnetic field pattern of a bar magnet?

Ans:

• The two ways by which we can trace the magnetic field pattern of a bar magnet are as follows:
• The magnetic field lines pattern due to bar magnet can be plotted using iron filings.
• The magnetic field lines pattern due to a bar magnet can be plotted using a compass.

3) You are given the magnetic field pattern of a magnet. How will you find out from it where the magnetic field is the strongest?

Ans:

As we know that the properties of magnetic field lines, the magnetic field is strongest at the region where magnetic field lines are closed together.So we can identify the region of strong magnetic field.

4) State whether the following statement is true or false: The axis of earth’s imaginary magnet and the geographical axis coincide with each other.

Ans:

The above-mentioned statement is false.

And the correct statement is, the axis of earth’s magnetic field is inclined at an angle of about 15° with the geographic axis.

5) Why does a compass needle get deflected when brought near a bar magnet?

Ans:

• The compass needle gets deflected when a a bar magnet is brought near to it because bar magnet exerts the magnetic force on the needle of compass and needle itself is the tiny pivoted magnet which is free to move in the horizontal plane.
• Due to which the compass needle gets deflected.

6) Where do the manufacturers use a magnetic strip in the refrigerator? Why is this magnetic strip used?

Ans:

Manufacturer use a magnetic strip in the refrigerator door to keep the door of refrigerator closed properly.

7) Fill in the following blanks with suitable words:

Ans:

(a) Magnetic field lines leave the north pole of a bar magnet and enters at its south

(b) The earth’s magnetic field is rather like that of a bar magnet with its south pole in the northern hemisphere.

8) Draw a diagram to show the magnetic field lines around a bar magnet.

Ans:

Following diagram shows the magnetic field lines around the bar magnet. 9) What is a magnetic field? How can the direction of magnetic field lines at a place be determined?

Ans:

• Magnetic field is the space surrounding a magnet in which the magnetic force is exerted.
• And the direction of magnetic at any point is nothing but the direction of resultant force acting on the hypothetical north pole placed at that point.
• Thus, north end of the needle of compass indicates the direction of magnetic field at a point where we placed it.

10) Explain why, two magnetic field lines do not intersect each other.

Ans:

• The magnetic field lines do not intersect each other because the resultant force on the north pole at any point can be acting only in one direction.
• And if two magnetic field lines are intersecting one another then the resultant force acting on the north pole placed at that point of intersection will be acting along the two directions and which is not possible.
• Hence, magnetic field lines do not intersect each other.

11) When an electric current is passed through any wire, a magnetic field is produced around it. Then why an electric iron connecting cable does not attract nearby iron objects when electric current is switched on through it?

Ans:

• When an electric current is passed through any wire then magnetic field is produced around it.
• But this magnetic field produced is very weak due to which an electric iron connecting cable does not attract the nearby iron objects when electric current is switched on through it.

12) (a) Define magnetic field lines. Describe an activity to draw a magnetic field line outside a bar magnet from one pole to another pole.

(b) Explain why, a freely suspended magnet always points in the north-south direction.

Ans:

a)

• Magnetic field lines are the path traced by the north magnetic pole free to move under the influence of a magnetic field. Also, magnetic filed lines are the lines drawn in the magnetic field along which the magnetic north pole would move freely.
• The magnetic field lines are also called as magnetic lines of force.

Activity for drawing magnetic field lines outside a bar magnet from one pole to another pole:

• We place a thick card paper over the strong bar magnet. With the help of sprinkler, we spread the thin layer of iron filings over the card by tapping the card gently.
• Then we can see that, the iron filings arrange themselves in a particular regular pattern which gives the rough picture of magnetic field lines produced by the bar magnet.
• This happens because the bar magnet exerts the magnetic field around it and also the iron filings experience the force of magnetic field of the bar magnet.
• And this force of magnetic field of the bar magnet is responsible for the iron filings to arrange themselves in regular pattern.
• Mainly, the iron filings under the magnetic field force acts like tiny magnets and align them along the direction of magnetic field lines. In this way, we can draw the magnetic field lines produced by the bar magnet by showing the path of iron filings with the magnetic field lines.

b)

• A freely suspended magnet always points in the north south direction because the north pole of the magnet is attached to the south pole of the earth and south pole of the magnet is attached to the north pole of the earth.
• And due to this the freely suspended magnet always points in the north south direction.
• And this suggests us that earth itself behaves as a magnet which causes freely suspended magnet to point always in north south direction.

### Electromagnetism

1) Which effect of current can be utilised in detecting a current carrying wire concealed in a wall?

Ans:

Magnetic effect of current can be utilised in detecting a current carrying wire concealed in a wall.

2) What conclusion do you get from the observation that a current-carrying wire deflects a compass needle placed near it?

Ans:

We conclude from the observation that a current carrying wire deflects a compass placed near it that, a current flowing in a wire always gives rise to a magnetic field around it.

3) Name the scientist who discovered the magnetic effect of current.

Ans:

The magnetic effect of current discovered by Oersted in 1820.

4) State qualitatively the effect of inserting an iron core into a current-carrying solenoid.

Ans:

The effect of inserting an iron core into a current carrying solenoid is that the magnetic field becomes very strong.

5) Name the rule for finding the direction of magnetic field produced by a straight current-carrying conductor.

Ans:

Maxwell’s right hand thumb rule is used to find the direction of magnetic field produced by a straight current carrying conductor.

6) State the form of magnetic field lines around a straight current-carrying conductor.

Ans:

The magnetic field lines around a straight current carrying conductor is in the form of concentric circles with centre are along the axis of the conductor.

7) What is the other name of Maxwell’s right-hand thumb rule?

Ans:

The Maxwell’s right hand thumb rule is also known as Maxwell’s corkscrew rule.

8) State whether the following statement is true or false: The magnetic field inside a long circular coil carrying current will be parallel straight lines.

Ans:

The magnetic field inside a long circular coil carrying current will be parallel straight lines, is the true statement.

9) What is the shape of a current-carrying conductor whose magnetic field pattern resembles that of a bar magnet?

Ans:

The shape of the current carrying conductor whose magnetic field pattern resembles that of a bar magnet is the solenoid.

10) State three ways in which the strength of an electromagnet can be increased.

Ans:

We can increase the strength of an electromagnet by following ways:

• By increasing the number of turns in the coil.
• By increasing the current flowing in the coil.
• By reducing the length of air gap between its poles.

11) Fill in the following blanks with suitable words:

Ans:

(a) The lines of magnetic field round a straight current carrying conductor are in the shape of concentric circles.

(b) For a current carrying solenoid, the magnetic field is like that of a bar magnet.

(c) The magnetic effect of a coil Can be increased by increasing the number of turns, increasing the current, or inserting an iron

(d) If a coil is viewed from one end and the current flows in an anticlockwise direction, then this end is a north

(e) If a coil is viewed from one end and the current flows in a clockwise direction, then this end is a south

12) Describe how you will locate a current-carrying wire concealed in a wall.

Ans:

• We can locate the current carrying wire concealed in a wall using plotting compass which produces magnetic effect of current and it can be easily helpful to us to locate a current carrying wire concealed in a wall.
• When we move the plotting compass near to the current carrying wire its needle shows deflection only at that place where there is current carrying wire is concealed in a wall.
• In this way, we can locate the current carrying wire concealed in a wall.

13) Describe some experiment to show that the magnetic field is associated with an electric current.

Ans:

To describe the experiment showing that the magnetic field is associated with an electric current we do following experiment: • We have taken a thick insulated copper and fixed it in such way that the portion AB of the wire is in the north-south direction as shown in figure below.
• And we placed a plotting compass M under this wire AB, and we connected the two ends of the wire to battery through the switch.
• We observe that, when there is no current is flowing through the wire AB then the needle of the compass is parallel to the wire AB as in north-south direction.
• Now, we pass the electric current through the wire AB by closing the switch, after that we observed that the compass needle get deflected from its north-south direction as shown in the figure. And when we open the switch then current stops flowing through the wire AB and hence compass needle returns to its original position i.e. parallel to the direction of wire AB in north-south direction.
• As we already know that, the compass needle deflects from north-south direction only when there will be a force acting on it due to another magnetic field.
• And this shows that, the current flowing through the wire AB produces the magnetic field which deflects the needle of plotting compass.
• And it is also observed that, if we reversed the direction of current by reversing the connections of battery then the deflection of needle is in opposite directions takes place.
• This experiment proves the presence of magnetic field associated with an electric current.

14) (a) Draw a sketch to show the magnetic lines of force due to a current-carrying straight conductor.

(b) Name and state the rule to determine the direction of magnetic field around a straight current-carrying conductor.

Ans:

a)

Following diagram shows the magnetic lines of force due to a current carrying straight conductor: b)

• The direction of magnetic field around a straight current carrying conductor us determined by using Maxwell’s right hand thumb rule.
• According to which, we assume that if we are holding the current carrying wire in our right hand in such way that our thumb points in the direction of current then the fingers curled the wire gives the direction of magnetic field around the wire.
• In short, when we stretch the thumb of right hand in such way that the fingers are curled around it. And if the thumb gives the direction of current then the curled fingers gives the direction of magnetic field.

15) State and explain Maxwell’s right-hand thumb rule.

Ans:

Maxwell’s right hand thumb rule:

• According to Maxwell’s right hand thumb rule, we assume that if we are holding the current carrying wire in our right hand in such way that our thumb points in the direction of current then the fingers curled the wire gives the direction of magnetic field around the wire.
• In short, when we stretch the thumb of right hand in such way that the fingers are curled around it. And if the thumb gives the direction of current then the curled fingers gives the direction of magnetic field.

16) What is Maxwell’s corkscrew rule? For what purpose is it used?

Ans:

Maxwell’s right hand thumb rule is also called as Maxwell’s corkscrew rule. According to which, if we imagined that driving a corkscrew in the direction of current then the direction the direction in which we turn the handle of corkscrew gives the direction of magnetic field or magnetic field lines.

Maxwell’s corkscrew rule is used to determine the direction of magnetic field.

17) (a) Draw the magnetic lines of force due to a circular wire carrying current.

(b) What are the various ways in which the strength of magnetic field produced by a current-carrying circular coil can be increased?

Ans:

a) The following diagram shows the magnetic lines of force due to a circular wire carrying current. b)

• As the strength of magnetic field produced by a circular coil carrying current is directly proportional to number of turns, current and inversely proportional to its radius of the coil.
• Hence, the strength of magnetic field produced by a current carrying circular coil can be increased by increasing the number of turns n of coil, also by increasing the current I flowing through the coil and by decreasing the radius of the coil.

18) State and explain the Clock face rule for determining the polarities of a circular wire carrying current.

Ans:

According to Clock face rule, if we are looking at one face of the circular wire through which current is passing

• If the current around the circular coil is in clockwise direction, then the face of the circular coil will be the south pole.
• And if the current around the circular coil is in the anticlockwise direction, then that face of the circular coil will be north pole.

19) Name any two factors on which the strength of magnetic field produced by a current-carrying solenoid depends. How does it depend on these factors?

Ans:

The strength of magnetic field produced by a current carrying solenoid depends on the following factors:

• The number of turns in the solenoid: if the number of turns in the solenoid are increased then the strength of the magnet field produced by solenoid also increases.
• The strength of the current in the solenoid: if the current in the solenoid is larger then the magnetic field produced is also stronger.
• The nature of the core material used in the coil: if the soft iron rod is used as core in solenoid, then magnetic field produced has greater strength.

20) (a) Draw a circuit diagram to show how a soft iron piece can be transformed into an electromagnet.

(b) Describe how an electromagnet could be used to separate copper from iron in a scrap yard.

Ans:

a) The following diagram shows the how soft iron piece can be transformed into an electromagnet. b)

• Electromagnets are used to separate copper from iron in a scrap yard due to its high magnetic field.
• The strong electromagnets are inserted in the scrap yard containing copper and iron and when current of electromagnets is switched on then it carries the iron pieces to their location from the mixture of copper and iron. And again by switching off the current of electromagnets it dropped the iron objects.
• In this way, by switching on and off the current of electromagnet we can separate the copper from iron in scrap yard.

21) (a) How does an electromagnet differ from a permanent magnet?

(b) Name two devices in which electromagnets are used and two devices where permanent magnets are used.

Ans:

a)

Electromagnet:

• Electromagnet is the temporary magnet whose magnetism can be switched on or off by passing the current through it or by stopping it.
• Electromagnet produces the magnetic field of strong force.
• As the strength of magnetic field produced by electromagnets depends on the current flowing through it and number of turns in it. Hence the strength of magnetic field can be increased by increasing current and number of turns in electromagnet.
• By changing the direction of current in the circuit we can change the polarity of the electromagnet.

Permanent magnet:

• The bar magnet is called as the permanent magnet.
• The magnetic field produced by permanent magnet is weak as compared to electromagnets.
• The strength of the magnet field produced by permanent magnet remains constant and cannot be changed.
• We cannot change the polarity of the permanent magnet.

b)

• Following are the devices where electromagnets are used: -Electric bell, electric motors etc.
• Following are the devices where permanent magnet are used:- Refrigerator doors, toys etc.

22) (a) What is a solenoid? Draw a sketch to show the magnetic field pattern produced by a current-carrying solenoid.

(b) Name the type of magnet with which the magnetic field pattern of a current-carrying solenoid resembles.

(c) What is the shape of field lines inside a current-carrying solenoid? What does the pattern of field lines inside a current-carrying solenoid indicate?

(d) List three ways in which the magnetic field strength of a current-carrying solenoid can be increased?

(e) What type of core should be put inside a current-carrying solenoid to make an electromagnet?

Ans:

a)

• Solenoid is the coil which consist of large number of turns which closed together of insulated copper wire.
• The following diagram shows the magnetic field pattern produced by a current carrying solenoid. b)

Bar magnet is the type of magnet with which the magnetic field pattern of a current carrying solenoid resembles.

c)

The magnetic field lines inside the solenoid are in the form of straight parallel lines which indicates the strength of magnetic field is same at all points inside the solenoid i.e. magnetic field is uniform inside the solenoid.

d)

Following are the three ways through which we can increase the strength of magnetic field produced by current carrying solenoid:

• By increasing the number of turns in the solenoid.
• By increasing the strength of the current inside the solenoid.
• By using soft iron rod as core material in making solenoid.

e)

By placing soft iron rod inside a solenoid, we can increase the strength of magnetic field which is due to iron get magnetised by induction. And hence electromagnet is formed.

23) (a) What is an electromagnet? Describe the construction and working of an electromagnet with the help of a labelled diagram.

(b) Explain why, an electromagnet is called a temporary magnet

(c) Explain why, the core of an electromagnet should be of soft iron and not of steel.

(d) State the factors on which the strength of an electromagnet depends. How does it depend on these factors?

(e) Write some of the important uses of electromagnets.

Ans:

a)

An electromagnet is the temporary magnet which consist of a long coil of insulated copper wire which is enclosed around the soft iron core which is magnetised only when we pass the electric current through it.

• The following diagram shows the simple electromagnet.
• To construct an electromagnet, we have to take soft iron rod NS and on which we have wounded a coil of insulated copper wire.
• By connecting the two ends of the copper coil to a battery electromagnet will be formed.
• Iron core is used in making electromagnet because when current passing through the coil is switched off then it loses its all magnetism.
• Hence, electromagnet is the temporary magnet. b)

An electromagnet is called as temporary magnet because the magnetic field produced by it remains till the current is flowing through the coil. And if the current is stopped then there will be no magnetic field is produced.

c)

• In constructing the electromagnets soft iron is used as core because after stopping the current through the coil, copper loses all its magnetism and there will be magnetic field is produced.
• While if we used steel as core instead of soft iron then after stopping the current, the steel also not loses its magnetism and there will be some magnetic field is retained.
• Hence soft iron is used as core in constructing electromagnets.

d)

Following are the factors on which strength of the electromagnets depends:

• Number of turns of the coil: If we increased the number of turns of the coil then the strength of the electromagnets increases.
• Current flowing through the coil: If we increased the current through the coil then the strength of the electromagnet also increases.
• Length of the air gap between the poles: If we reduced the length of air gap between the poles of the electromagnet then the strength of the electromagnets also increases.

### Magnetism In Human Beings

1) What produces magnetism in the human body?

Ans:

An electric impulse creates temporary magnetism in human body.

2) Name one medical technique which is based on magnetism produced in human body. For what purpose is this technique used?

Ans:

The technique which is based on magnetism produced in human body is Magnetic Resonance Imaging MRI.

MRI is used to obtain images of the internal parts of our body.

3) Name two human body organs where magnetism produced is significant.

Ans:

The two main organs of the human body where the magnetic field produced is quite significant are the heart and the brain.

4) What is the full form of MRI?

Ans:

The full form of MRI is Magnetic Resonance Imaging.

5) Name the technique by which doctors can produce pictures showing insides of the human body.

Ans:

By the technique of MRI scans doctors can produce pictures showing insides of the human body.

6) Name one technique which can detect cancerous tissue inside the body of a person.

Ans:

The MRI technique can detect the cancerous tissue inside the body of a person.

### Force On Current Carrying Conductor placed in Magnetic Field

1) What happens when a current-carrying conductor is placed in a magnetic field?

Ans:

When a current carrying conductor is placed in magnetic field then mechanical force is exerted on the conductor which is responsible for the motion of the conductor.

2) When is the force experienced by a current-carrying conductor placed in a magnetic field largest?

Ans:

When the current carrying conductor is perpendicular to the direction of magnetic field then the magnetic field produced is largest.

3) In a statement of Fleming’s left-hand rule, what do the following represent?

(a) direction of centre finger.

(b) direction of forefinger.

(c) direction of thumb.

Ans:

According to Fleming’s left-hand rule,

• Direction of centre finger indicates the direction of current.
• Direction of forefinger indicates the magnetic field direction.
• Direction of thumb indicates the direction of force acting on the conductor.

4) Name one device which works on the magnetic effect of current.

Ans:

An electric motor is the device which works on the magnetic effect of current.

5) Name the device which converts electrical energy into mechanical energy.

Ans:

An electric motor is the device which converts electrical energy into mechanical energy.

6) A motor converts one form of energy into another. Name the two forms.

Ans:

An electric motor converts an electrical energy into the mechanical energy.

7) State whether the following statement is true or false: An electric motor converts mechanical energy into electrical energy.

Ans:

The above statement is false.

Because an electric motor is the device which converts electrical energy into mechanical energy.

8) For Fleming’s left-hand rule, write down the three things that are 90° to each other, and next to each one writes down the finger or thumb that represents it.

Ans:

• For Fleming’s left hand rule, magnetic field produced, current flowing through conductor and force acting on conductor which is responsible for the motion of conductor are mutually perpendicular to each other.
• The forefinger gives the direction of magnetic field, the centre finger gives the direction of current and the thing gives the direction of motion of conductor.

9) Name the device which is used to reverse the direction of current in the coil of a motor.

Ans:

Commutator is the device which is used to reverse the direction of current in the coil of motor.

10) What is the other name of the split ring used in an electric motor?

Ans:

The other name of split ring used in an electric motor is the commutator.

11) What is the function of a commutator in an electric motor?

Ans:

The function of commutator in an electric motor is to reverse the direction of current through the circuit.

12) Of what substance are the brushes of an electric motor made?

Ans:

The brushes of an electric motor are made from carbon.

13) Of what substance is the core of the coil of an electric motor made?

Ans:

The coil of an electric motor is made from insulated copper wire.

14) In an electric motor, which of the following remains fixed and which rotates with the coil? Commutator; Brush

Ans:

• In an electric motor the brush remains fixed.
• And commutator rotates with the coil.

15) What is the role of the split ring in an electric motor?

Ans:

The role of split rings in an electric motor is that it reverses the direction of current flowing through the coil every time when the coil the is passing the vertical position during its rotation.

16) Fill in the following blanks with suitable words:

Ans:

(a) Fleming’s rule for the motor effect uses the left.

(b) A motor contains a kind of switch called a commutator which reverses the current every half rotation.

17) (a) A current-carrying conductor is placed perpendicularly in a magnetic field. Name the rule which can be used to find the direction of force acting on the conductor. (b) State two ways to increase the force on a current-carrying conductor in a magnetic field.

(c) Name one device whose working depends on the force exerted on a current-carrying coil placed in a magnetic field.

Ans:

a)

A current carrying conductor is placed perpendicular in a magnetic field then Fleming’s left-hand rule is used to find the direction of force acting on the conductor.

b)

The force acting on a current carrying conductor in a magnetic field can be increased by following ways:

• By increasing the current flowing through the conductor.
• By increasing the strength of the magnet field.

c)

Electric motor is the devise whose working depends on the force exerted on a current carrying coil placed in a magnetic field.

18) State Fleming’s left-hand rule. Explain it with the help of labelled diagrams.

Ans:

According to Fleming’s left-hand rule, if we hold the left hand in a such way that forefinger, middle finger and thumb are mutually perpendicular to each other. And if forefinger is in the direction of magnetic field and middle finger is in the direction of current then the thumb of left gives the direction of force acting on the conductor.

The following diagram shows the Fleming’s left-hand rule. 19) What is the principle of an electric motor? Name some of the devices in which electric motors are used.

Ans:

In an electric motor magnetic effect of current is used. Electric motor is based on the principle that when a rectangular coil is placed in the magnetic field and if we pass the current through it then there will be a force acting on the coil which is responsible for the rotation of coil continuously.

Following are the devices in which electric motor is used:

Electric fans, coolers, mixers, refrigerators, grinders, washing machines etc.

20) (a) In a d.c. motor, why must the current to the coil be reversed twice during each rotation?

(b) What device reverses the current?

Ans:

a)

In a DC motor, the current through the coil is reversed after every half rotation. And this reversing of current causes the continuous rotation of coil till the current is passed through the coil.

b)

Commutator is the device which is used to reverse the current flowing through the coil.

21) (a) State what would happen to the direction of rotation of a motor if:

(i) the current was reversed

(ii) the magnetic field were reversed

(iii) both current and magnetic field were reversed simultaneously.

(b) In what ways can a motor be made more powerful?

Ans:

a)

1) if the direction of current is reversed in an electric motor, then direction of rotation would also be reversed.

2) if the magnetic field also be reversed then also the direction of rotation is reversed

3) if both current and magnetic field were reversed simultaneously then the direction of rotation remains unchanged.

b)

Motor can be made powerful by increasing the number turns in the coil and by winding the coil on soft iron core.

22) (a) What is an electric motor? With the help of a labelled diagram, describe the working of a simple electric motor.

(b) What are the special features of commercial electric motors?

Ans:

a)

Electric motor is a rotating device which converts electrical energy into mechanical energy. The figure shows the labelled diagram of simple electric motor. Fig. Electric Motor

Working of an electric motor:

• It has rectangular coil ABCD insulated by copper wire. The coil is placed between two poles of magnet such that the sides AB and CD are normal to the direction of magnetic field.
• The ends of coil are connected to halves P and Q whose inner sides are insulated and are attached to axle. The edges of P and Q are touching to two conducting stationary brushes X and Y. Current will enter the coil through brush X and flows back to battery through Y. By applying Fleming’s left-hand rule, the force acting on side AB pulls it downwards and force acting on CD pulls it up words, due to which the coil and axle rotates freely in anticlockwise direction.
• After half rotation Q meet to brush X and P meets to brush Y. In this way current get reversed and flows along the path DCBA. Commutator is the device which reverse the direction of current through circuit. Here split rings act as a commutator.
• When the direction of current is reversed, the force acting on sides AB and CD get also reversed, therefore the next half turn would be in same direction. The direction of current is repeating continuously due to which the coil and axle rotate continuously

b) Following are the special features of commercial electric motor:

• The coil should be wound on soft iron core which increases the strength of the magnet field. And hence motor becomes more powerful.
• Also, the coil contains large number of turns of the insulated copper wire.
• And instead of permanent magnet a string powerful electromagnet is used.

### Electromagnetic Induction

1) Name the device which converts mechanical energy into electric energy-

Ans:

Electric generator is the device which is used to convert mechanical energy into electrical energy.

2) Out of an A.C. generator and a D.C. generator:

(a) which one uses a commutator (split rings)?

(b) which one uses slip rings?

Ans:

a) DC generator uses a commutator or split rings.

b) AC generator uses slip rings.

3) Name the phenomenon which is made use of in an electric generator.

Ans:

Electromagnetic induction is the phenomenon which is made use of in an electric generator.

4) Name the rule which gives the direction of induced current.

Ans:

Fleming’s right-hand rule gives the direction of induced current.

6) What condition is necessary for the production of current by electromagnetic induction?

Ans:

When there is a relative motion between the coil carrying current and the magnet then only the phenomenon of electromagnetic induction will occur.

7) What type of generator is used at Power Stations?

Ans:

In power stations AC generator is used.

8) What change should be made in an a.c. generator so that it may become a d.c.generator?

Ans:

If we replaced the slip rings in an AC generator by a commutator then it will become a DC generator.

9) State whether the following statements are true or false:

(a) A generator works on the principle of electromagnetic induction.

(b) A motor works on the principle of electromagnetic induction.

Ans:

a) The above statement is true because generator works on the principle of electromagnetic induction.

b) The above statement is false because motor works on the principle of magnetic effect of electric current.

10) What is the function of brushes in an electric generator?

Ans:

In electric generator brushes are used to transfer the electric current from the coil to the external circuit.

11) When a wire is moved up and down in a magnetic field, a current is induced in the wire. What is this phenomenon known as?

Ans:

When a wire is moved up and down in a magnetic field then current is induced in the wire and this phenomenon is called as electromagnetic induction.

12) When current is ‘switched on’ and ‘switched off’ in a coil, a current is induced in another coil kept near it. What is this phenomenon known as?

Ans:

When a current is switched on and switched off in a coil then current is induced in another coil kept near to it. And this phenomenon is called as the electromagnetic induction.

13) What is the major difference between the simple alternator and most practical alternators?

Ans:

The major difference between simple alternator and most practical alternators is as follows:

• In simple alternator, magnet is fixed and coil is rotating.
• While in practical alternators, coil is made fix and magnets are rotating.

13) Why are Thermal Power Stations usually located near a river?

Ans:

Thermal power stations are usually located near a river because water is used for making steam which helps in turning the turbines. Also, water is used for cooling the steam so that it can be condensed and converted into hot water and again a fresh steam is generated.

14) List three sources of magnetic fields.

Ans:

Following are the sources of magnetic field:

Permanent magnets, electromagnets and current carrying conductors like straight wire, circular coil and solenoid.

15) Complete the following sentence: A generator with commutator produces………..current.

Ans:

A generator with commutator produces direct current.

16) Two circular coils A and B are placed close to each other. If the current in coil A is changed, will some current be induced in the coil B? Give reason for your answer.

Ans:

• Given that, two circular coils are placed close to each other. If the current in coil A is changed then the magnetic field around the coil A also changes. And this change in magnetic field around the coil A changes the magnetic field around the coil B also.
• As a result, the change in magnetic field around the coil B induces the electric current in it.

17) (a) Explain the principle of an electric generator.

(b) State two ways in which the current induced in the coil of a generator could be increased.

Ans:

a)

• Electric generator works on the principle of electromagnetic induction.
• According to that principle, when a straight conductor is moved in magnetic field then it induces the current in the conductor.

b)

Following are the two ways by which we can increase current induced in the coil of generator.

• By increasing the speed of rotation of coil in generator
• And by using the coil which is having large area.

18) (a) What is the difference between alternating current and direct current?

(b) What type of current is given by (i) a dry cell, and (ii) a Power House generator?

Ans:

a) DC current: • In DC current charge flows only in one direction and hence it is also called as uni-directional current.
• Frequency of DC current is zero. The magnitude of DC current is fixed or constant. DC circuit possesses mostly register only.
• The power factor for DC circuits is always 1.
• In DC circuits there is a high energy loss.
• DC circuits are not used for long distance transmission because of high energy losses.

AC current: • In AC currents, charge flows in both direction that is AC current changes its direction periodically and hence it is also called as bidirectional current.
• In India frequency of AC is 50 Hz.
• The magnitude of AC current is varying with time.
• AC circuit possesses registers, capacitors and inductors also.
• The power factor for AC circuit is lies between 0 and 1.
• There are low energy losses for AC circuits.

b)

The current given by dry cell is the DC current while the current given by power house generator is the alternating current.

19) State and explain Fleming’s right-hand rule.

Ans:

The Fleming’s right-hand rule is stated as below:

If we hold the forefinger, middle finger and thumb of right hand such that they are mutually perpendicular to each other. And if forefinger gives the direction of magnetic field, thumb gives the direction of motion of conductor then middle finger gives the direction of induced current in the conductor.

20) Name and state the rule to find the direction of:

(a) current induced in a coil due to its rotation in a magnetic field.

(b) force experienced by a current-carrying straight conductor placed in a magnetic field which is perpendicular to it.

Ans:

(a) Fleming’s right-hand rule is used to find the direction of current induced in a coil due to its rotation in a magnetic field.

(b) Fleming’s left-hand rule is used to find the direction of force experienced by a current carrying straight conductor placed in a magnetic field which is perpendicular to it.

21) (a) In what respect does the construction of an A.C. generator differ from that of a D.C. generator?

(b) What normally drives the alternators in a Thermal Power Station? What fuels can be used to heat water in the boiler?

Ans:

a)

• The main point of difference between construction of AC generator and DC generator is based on the connections of ends of the coil.
• In ac generator two ends of the coil are connected to slip rings while in DC generator the two ends of the coil are connected to commutator.

b)

High pressure steam is normally driving the alternators in a thermal power station. And the fuels used are coal, natural gas, oil etc.

22) Draw the labelled diagram of an A.C. generator. With the help of this diagram, explain the construction and working of an A.C. generator.

Ans:

An AC generator is an electronic device which is used to convert mechanical energy into electrical energy. The labelled circuit diagram of electric generator is as shown in figure. Construction and working:

• It consists of a rotator coil PQRS which has been placed in between two poles of magnet the end points of coil are connected to two rings R1 and R2. B1 and B2 are the brushes and axel is attached internally to this rings. The outer ends of brushes are directly connected to the galvanometer for measuring current.
• When the coil PQRS is rotating in clockwise direction then according to Fleming’s right-hand rule, the current is induced in side PQ and RS. The current to the coil depends on number of turns. If number of turns increased current get added up and galvanometer shows large deflection. After half rotation, the direction of current induced changes. Hence the direction of current changes after every half rotation which is called as an AC current and this device is called AC generator.
• To produce a uni directional DC current we have to use a split ring type of commutator, due to which each brush will be in contact with only one arm and hence uni-directional current flows called as DC current like in an electric motor.

23) (a) What do you understand by the term “electromagnetic induction”? Explain with the help of a diagram.

(b) Name one device which works on the phenomenon of electromagnetic induction.

(c) Describe different ways to induce current in a coil of wire.

Ans:

a)

• When a wire is moved up and down in a magnetic field then current is induced in the wire and this phenomenon is called as electromagnetic induction.
• Given that, two circular coils are placed close to each other. If the current in coil A is changed then the magnetic field around the coil A also changes. And this change in magnetic field around the coil A changes the magnetic field around the coil B also.
• As a result, the change in magnetic field around the coil B induces the electric current in it.
• And this phenomenon is called as electromagnetic induction.

b)

Electric generator is the device which works on the phenomenon of electromagnetic induction.

c)

Following are the ways to induce current in the coil:

• A current is induced in the coil when we moved the coil relative to the fixed magnet.
• When we moved the magnet relative to the fixed coil then also current is induced in the coil.

24) (a) What do you understand by the terms ‘direct current’ and ‘alternating current’?

(b) Name some sources of direct current and some of alternating current.

(c) State an important advantage of alternating current over direct current.

(d) What is the frequency of A.C. supply in India?

Ans:

a) DC current: • In DC current charge flows only in one direction and hence it is also called as uni-directional current.
• Frequency of DC current is zero. The magnitude of DC current is fixed or constant. DC circuit possesses mostly register only.
• The power factor for DC circuits is always 1.
• In DC circuits there is a high energy loss.
• DC circuits are not used for long distance transmission because of high energy losses.

AC current: b)

• The sources of direct current are: dry cell, battery, car battery and dc generators etc.
• The sources of alternating current are: AC generators, power stations etc.

c) Following are the important advantages of alternating current over direct current:

• The alternating current can be transferred to long distance as compared to dc.
• The power less during transmission of AC is less as compared to DC.
• We can easily convert AC into DC.
• There are low energy losses for AC circuits.

d)

The frequency of AC supply in India is 50 Hz.

### Domestic Electric Circuits

1) What name is given to the device which automatically cuts off the electricity supply during short-circuiting in household wiring?

Ans:

The devise which automatically cuts off the electricity supply during short circuiting in household wiring is the electric fuse.

2) What is the usual capacity of an electric fuse used

(i) in the lighting circuit, and

(ii) in the power circuit, of a small house?

Ans:

1)

The usual capacity of an electric fuse used in the lighting circuit is near about 5A.

2)

The usual capacity of an electric fuse used in the power circuit of small house is near about 15A.

3) Give the symbol of an electric fuse used in circuit diagrams.

Ans:

The following figure shows the symbol of an electric fuse used in circuit diagrams. 4) State whether the following statements are true or false:

(a) A wire with a green insulation is usually the live wire.

(b) A miniature circuit breaker (MCB) works on the heating effect of current.

Ans:

a)

A wire with a green insulation is usually the live wire. This statement is false.

Because the wire with green insulation is the earth wire.

b)

A MCB works on the heating effect of  current . This statement is false.

Because MCB works on the magnetic effect of current.

5) Along with live wire and neutral wire, a third wire is also used in domestic electric wiring. What name is given to this third wire?

Ans:

Along with live wire and neutral wire, a third wire is also used in domestic electric wiring which is called as earth wire.

6) List the colours of the three wires in the cable connected to the plug of an electric iron.

Ans:

• The electrical appliances like electric iron, electric kettle, water heater, room cooler or refrigerators contains three insulated copper wires having different colours.
• The wire with red colour insulation is the live wire.
• The wire with black colour insulation is the neutral wire.
• The wire with green wire is the earth wire.

7) What is the electric potential of the neutral wire in a mains supply cable?

Ans:

The electric potential of the neutral wire in a mains supply cable is the 0 volt.

8) If fuses of 250 mA, 500 mA, 1 A, 5 A and 10 A were available, which one would be the most suitable for protecting an amplifier rated at 240 V, 180 W?

Ans:

Given that,

V= 240V

P= 180 W

We know that, electric power is given by,

P= VI

Hence, I= P/V = 180/240= 0.75 A

Thus, the fuse with capacity 1A is most suitable for protecting given amplifier.

9) When does an electric short circuit occur?

Ans:

When there is direct contact between the live wire and the neutral wire occurs then short circuiting takes place.

10) In which wire in an A.C. housing circuit is the switch introduced to operate the lights?

Ans:

In live wire in an AC housing circuit is the switch introduced to operate the lights.

11) In household circuits, is a fuse wire connected in series or in parallel?

Ans:

In household circuits fuse wire is connected in series.

12) Usually three insulated wires of different colours are used in an electrical appliance. Name the three colours.

Ans:

Usually three insulated wires of different colours are used in an electrical appliances.

The wire with red coloured insulation is the live wire, the wire with black colour insulation is the neutral wire and the wire with green colour insulation is the earth wire.

13) What is the usual colour of the insulation of: (a) live wire, (b) neutral wire, and (c) earth wire?

Ans:

The usual colours of insulation of the wires are as follows.

• A) The live wire has red coloured insulation.
• b) The neutral wire has black coloured insulation.
• C) The earth wire has green coloured insulation.

14) What is the main purpose of earthing an electrical appliance?

Ans:

The metal body of an electrical appliances is earthed to avoid the risk of electric shocks and to protect us from such electric shocks.

15) Give two reasons why different electrical appliances in a domestic circuit are connected in parallel.

Ans:

• The different electrical appliances in a domestic circuits are connected in parallel because if any one of the appliance or circuit become faulty then it’s fuse get melted and there will be no effect on other electrical appliances and other circuit till works.
• Also, in parallel combination the voltage drop across each of the electrical equipment is same and hence they will draw the current according to their rating.

16) How should the electric lamps in a building be connected so that the switching on or off in a room has no effect on other lamps in the same building?

Ans:

If we connect electric lamps in parallel in a building then the switching on or off in a room has no effect on other lamps in the same building.

17) Fill in the following blanks with suitable words:

Ans:

a) A fuse should always be placed in the live wire of a mains circuit.

b) The earth wire should be connected to the body of an appliance.

18) (a) Of what substance is the fuse wire made? Why?

(b) Explain why, a copper wire cannot be used as a fuse wire.

Ans:

a)

The fuse wire is usually made from the tin plated copper wire having low melting point. Because  the fuse wire has to melt easily when there is magnetic effect of current and by this the whole electrical circuit get stopped and will be protected.

b)

A copper wire cannot be used as a fuse wire because it has high melting point and hence it does not melt easily when short circuit occurs. And hence temperature may get increased due to which there will be damage to electrical appliances cause.

19) What type of electric fuse is used in electrical appliances like car stereos? Explain with the help of a labelled diagram.

Ans: • Cartridge fuse is the electric fuse used in electrical appliances like car stereos.
• The following figure shows the diagram of cartridge fuse used in an electrical appliances.
• It consists of a glass tube T which is having a thin fuse wire sealed inside it. At the two ends of the glass tube there are two metal caps to which the two ends of fuse wire are connected.
• The metal caps are for connecting the fuse in an electric circuit in suitable manner.

20) Distinguish between the terms ‘overloading’ and ‘short-circuiting’ as used in domestic circuits.

Ans:

• The current flowing through the electrical appliances is dependent on the power rating of the appliances also. And if we connect too many electrical appliances having high power rating at the same time then they will draw very large current from the circuit.
• Overloading also may occur due to connecting many appliances to the single socket.
• Due to the flow of large current through the wire the copper wires of domestic circuit get heated and may cause fire also.

Short-circuiting:

• The live wire and neutral wires get touched when the plastic insulation of live wire and neutral wire get torn.
• This direct touching of live wire and neutral wire is called as the short-circuiting.
• When there is contact between the live wire and the neutral wire takes place then the resistance of the circuit becomes very small due which current flowing through the circuit is very large and hence heat will be generated creating a dangerous high temperature and finally may cause fire.

21) (a) When does a fuse cut off current? How does it do it?

(b) What is the maximum number of 60 W bulbs that can be run from the mains supply of 220 volts if you do not want to overload a 5 A fuse?

Ans:

a)

• When short-circuiting or overloading take place in household circuits, the current flowing through the circuit is very large and creates high temperature. If we have connected the fuse wire of proper rating in series with that circuit then at the time of heating the fuse wire get heated.
• As the melting point of fuse wire is less than the copper wires so that fuse wire get melted early and easily and helps in breaking the circuit.
• When the circuit become broken the electricity supply get stopped automatically before causing any damage to the rest of the electrical circuit and the also the electrical appliances.
• In this way, fuses helps in protecting the electrical circuit in our house.

b)

Given that,

P= 60W

V= 220V

I= 5A

We know that, the electric power is given by,

P= VI = 220*5= 1100W

So, total number of bulbs of 60W used will be = 1100/60= 18.33

Thus, 18 bulbs of 60W are used so that we do not overload a fuse of 5A.

22) Explain the importance of using in a household electric circuit (i) fuse, and (ii) earthing wire.

Ans:

1)

• When short-circuiting or overloading take place in household circuits, the current flowing through the circuit is very large and creates high temperature. If we have connected the fuse wire of proper rating in series with that circuit then at the time of heating the fuse wire get heated.
• As the melting point of fuse wire is less than the copper wires so that fuse wire get melted early and easily and helps in breaking the circuit.
• When the circuit become broken the electricity supply get stopped automatically before causing any damage to the rest of the electrical circuit and the also the electrical appliances.
• In this way, fuses helps in protecting the electrical circuit in our house.

2)

• The metal body of an electric appliances is earthed in order to avoid the electric shocks.
• That means the metal body of electrical appliances is connected to zero potential with the metal wire called as earth wire.
• One end of this earth wire is buried in the earth and one end is connected to metal body of electrical appliances. And hence the metal body of electrical appliances always remains at zero potential of the earth which is called as the electrical appliances are grounded or earthed.
• When baby current is flowing through the circuit the fuse wire get melted and power supply get blocked and heavy current flows through the earth wire and we get protected from the electric shocks.

23) (a) An electric iron is rated at 230 V, 750 W. Calculate

(i) the maximum current, and

(ii) the number of units of electricity it would use in 30 minutes.

(b) Which of the following fuse ratings would be suitable for this electric iron? 1 A, 3 A, 5 A, 13 A

Ans:

a)

Given that,

V= 230V

P= 750W

We know that, electric power is given by,

P= VI

Hence, I= P/V = 750/230= 3.26 A

Thus the maximum current will be 3.26A.

The electrical energy is given by,

E= PT = 750*1/2= 375 Wh = 0.375 kWh

Thus, the number of units of electricity used in 30 minutes will be 0.375kWh

b)

As the maximum current flowing through electric iron is 3.26A hence fuse of rating 5A is suitable for this electric iron.

24) What is the function of an earth wire? Why is it necessary to earth the metallic bodies of electrical appliances?

Ans:

• Earth wire protect us from electric shocks by flowing the current through it to the ground.
• The metal body of an electric appliances is earthed in order to avoid the electric shocks.
• That means the metal body of electrical appliances is connected to zero potential with the metal wire called as earth wire.
• One end of this earth wire is buried in the earth and one end is connected to metal body of electrical appliances. And hence the metal body of electrical appliances always remains at zero potential of the earth which is called as the electrical appliances are grounded or earthed.
• When baby current is flowing through the circuit the fuse wire get melted and power supply get blocked and heavy current flows through the earth wire and we get protected from the electric shocks.

25) (a) What current is taken by a 3-kW electric geyser working on 240 V mains?

(b) What size fuse should be used in the geyser circuit?

Ans:

a)

Given that,

P= 3kW = 3000W

V= 240V

We know that, electric power is given by

P= VI

Hence, I= P/V = 3000/240= 12.5 A

The current taken by electric geyser is 12.5A

b)

As the maximum current flowing through the geyser is 12.5A.

Hence, The fuse with rating 13A will be used in the geyser circuit.

26) (a) Why are fuses fitted in the fuse box of a domestic electricity supply?

(b) What device could be used in place of the fuses?

Ans:

a)

Electric fuses of proper rating are fitted in the fuse box of a domestic electricity supply because when there is short-circuiting or overloading occurs the large current produced will flows through the fuse wire which is connected in series with the circuit and it get melted . And hence the electricity supply get stopped due to which electrical appliances and the circuit will be protected.

b)

In place of the fuses the MCB could be used.

27) (a) Draw a labelled diagram to show the domestic electric wiring from an electric pole to a room. Give the wiring for a bulb and a three-pin socket only.

(b) State two hazards associated with the use of electricity.

(c) State the important precautions which should be observed in the use of electricity.

(d) What will you do if you see a person coming in contact with a live wire?

(e) Explain why, electric switches should not be operated with wet hands.

Ans:

a)

Following is the neat labelled diagram showing domestic electric wiring from an electric pole to a room. b)

Following are the hazards associated with the use of electricity:

• If we touch the a live electric wire we get a severe electric shock and sometimes it kills us.
• Short-circuiting due to damaged wiring or overloading in the circuit may causes the fire in the building.
• The loose connection and defects in switches , sockets, plugs may cause sparking and sometimes before also.

c)

Following are the important precautions which should be observed in the use of electricity:

• If we touched live electric wire or if there will be electric fire in our house then we have to switch off the main switch once so that electric power supply will be stopped. And in this we can prevent the spreading of fire.
• Sometimes if we ouches to the live wire then we must provided an insulated support of wood, plastic or rubber. We do not have to pull away the person who is in contact with the live wire.
• The electrical appliances like electric iron, cooler, refrigerators should be given earth connections to protect ourselves from severe electric shock.

d)

If we see the person in contact with the live wire then we don’t have to pull away the person instead of it we have to support him or pull away him by a insulated support of wood, plastic or rubber.

e)

We should never operate switches with wet hands or the plugs also not inserted into the sockets with wet hands because water is the conductor of electricity to some extent and hence touching the switches and sockets with wet hands may lead to electric shock also.

Here is your solution of Lakhmir Singh Class 10 Physics 2nd Chapter Magnetic Effect of Electric Current Solution

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Updated: May 28, 2022 — 4:13 pm