NCERT Solutions Class 10 Science Chapter 13 Magnetic Effects of Electric Current
NCERT Solutions Class 10 Science Chapter 13 Magnetic Effects of Electric Current: National Council of Educational Research and Training Class 10 Science Chapter 13 Solutions – Magnetic Effects of Electric Current. NCERT Solutions Class 10 Science Chapter 13 PDF Download.
NCERT Solutions Class 10 Science Chapter 13: Overview
Board |
NCERT |
Class |
10 |
Subject |
Science |
Chapter |
13 |
Chapter Name |
Magnetic Effects of Electric Current |
Topic |
Exercise Solutions |
NCERT Solutions Class 10 Science Chapter 13 – Magnetic Effects of Electric Current
Middle Exercise:
Page 224
1.) Why does a compass needle get deflected when brought near a bar magnet?
Ans:
- A compass needle is acts like a tiny magnet or small bar magnet.
- And the end points if the compass needle are pointing towards the north and south direction like as magnet. The end pointing towards the south direction is the south pole and the end pointing towards the north direction is the north pole. Hence, compass needle has some magnetic field around it.
- Thus, when we brought a compass needle near the bar magnet, the magnetic field of compass needle interacts with the magnetic field of bar magnet. Due to which compass needle shows the deflection when we brought it near to the bar magnet.
Page 228
1.) Draw a magnetic field line around a bar magnet?
Ans:
The following figure shows the magnetic field lines formed by the bar magnet.
2.) List the properties of magnetic field lines.
Ans:
Following are the properties of magnetic field lines:
- The magnetic field lines start from north pole and ends at south pole.
- While inside the magnet, the magnetic field lines are directed from its south pole to north pole which shows that magnetic field lines are closed curves.
- The degree of closeness of magnetic field lines gives the strength of the magnetic field at that point.
- More the lines are crowded greater is the strength of magnetic field.
- Magnetic field lines never cross each other.
3.) Why don’t two magnetic field lines intersect each other?
Ans:
- If there will be intersection of two or more magnetic field lines at a point then it shows that at that point the magnetic field has two directions. But we know that, magnetic field at a single point doesn’t have two directions and hence it is not possible.
- Because of this no two magnetic field lines intersect each other.
Page 229
1.) Consider a circular loop of wire lying in the plane of the table. Let the current pass through the loop clockwise. Apply the right-hand rule to find out the direction of the magnetic field inside and outside the loop?
Ans:
- Given that, the circular loop of wire lying in the plane of table through which current is passed in clockwise direction.
- If we applied right hand thumb rule to the left and right side of loop from inside then it is seen that magnetic field lines are entering into or going into the table as shown in figure.
- While when we apply right hand thumb rule outside the loop then it will be seen that, the magnetic field lines are coming out of the table or leaving the table.
2.) The magnetic field in a given reason is uniform. Draw a diagram to represent it.
Ans:
- When the magnetic field lines are directed in same direction which are parallel to each other as shown in following figure then we can say that it represents the magnetic field lines in a given reason is constant.
- The following diagram shows the uniform magnetic field.
3.) Choose the correct option.
The magnetic field inside a long straight solenoid carrying current
a) is zero
b) decreases as we move towards its end
c) increases as we move towards its end
d) is the same at all points
Ans:
d) is the same at all points
Because inside the long straight solenoid carrying current the magnetic field lines are parallel due to which the magnetic field inside the solenoid is constant.
Page 231 and 232
1.) Which of the following property of a proton can change while it moves freely in a magnetic field? (There may be more than one correct answer)
a) mass
b) speed
c) velocity
d) momentum
Ans: d) momentum
- We know that, momentum is the product of mass and velocity. When the proton is moving freely in a magnetic field then the mass of the proton remains constant but it’s velocity changes which means the momentum of the proton changes.
- Hence the correct option is d) momentum.
2.) In activity 13.7 how do we think the displacement of rod AB will be affected if a) current in rod AB is increased
b) a string horse shoe magnet is used and
c) length of the rod AB is increased.
Ans:
a)
Now if we increased current through the rod AB then it causes to increase the force on the conductor which leads to increase in the displacement of the rod AB.
b)
Now, if we used stronger horse shoe magnet then definitely it has strong magnetic field. And this strong magnetic field exerts the force on the conductor which causes the increase in the displacement of the rod AB.
c)
Now if we increased the length of the rod AB then also the force acting on the conductor increases.
3.) A positively charged particle (alpha particle) projected towards west is deflected towards north by a magnetic field. The direction of magnetic field is
a) towards south
b) towards east
c) downward
d) upward
Ans: d) upward
Because according to Fleming’s left hand rule the direction of magnetic field is upward.
Page 233
1.) State Flemings’left-hand rule.
Ans:
Fleming’s Left-hand rule:
According to Flemings’left-hand rule, if we stretched out thumb, forefinger and middle finger of our left hand in a such way that they are mutually perpendicular to each other than if the forefinger is giving direction of magnetic field and middle finger is giving the direction of current then the thumb gives the direction of motion or the direction of force acting on the conductor.
2.) What is the principle of an electric motor?
Ans:
- The principle of electric motor is based on the magnetic effect of electric current. According to which when a current carrying coil is placed in magnetic field then there will be force acting on the coil which rotates it. This is the principle of electric motor.
- Electric motor converts electrical energy into mechanical energy.
3.) What is the role of split ring in an electric motor?
Ans:
- In electric motor, split rings act as a commutator which reverse the direction of flow of current through the circuit. Due to reversing the current direction the magnetic force also gets reversed. And hence the coil is rotating continuously.
Page 236
1.) Explain different ways to induce current in a coil.
Ans:
Following are the different ways to induce current in the coil:
- The change in magnetic field around the coil induces the current inside it.
- When we move a coil continuously between strong magnetic field then also current is induced in the coil.
- In this way due to the phenomenon of electromagnetic induction the current induces in the coil.
Page 237
1.) State the principle of an electric generator.
Ans:
- The electric generator works on the principle of electromagnetic induction. When a straight conductor is continuously moved in a string magnetic field then current is induced in the conductor.
- By using this phenomenon in electric generator, mechanical energy is used to rotate the conductor in a magnetic field to produce electricity.
2.) Name some sources of direct current.
Ans:
Following are some sources of direct current:
- Dry cell battery, dry cell, car battery, solar cells, thermocouple etc.
3.) Which sources produces alternating current?
Ans:
Following are the sources which produces alternating current:
- AC generator, thermal power generator, nuclear power generator, hydroelectric power plants etc.
4.) Choose the correct option.
A rectangular coil of copper wire is rotated in a magnetic field. The direction of the induced current changes once in each
a) two revolutions
b) one revolution
c) half revolution
d) one fourth revolution
Ans: c) half revolution
Page 238
1.) Name two safety measures commonly used in electric circuits and appliances.
Ans:
- The important safety measure that is used in domestic wiring is, an electric fuse of proper rating is connected in series with the circuit which protects the while circuit and the electrical appliances from overloading and also from short circuiting.
- Also, proper earthing of electric circuit protects us from severe electric shocks.
2.) An electric oven of 2kW power rating is operated in a domestic electric circuit 220V that has a current rating of 5A. What result do you expect? Explain.
Ans:
Given that,
V= 220V
P= 2kW = 2000W
And we know that, an electric power is given by,
P= VI
Hence, current will be
I = P/ V = 2000/220= 9.09A
Thus, the current drawn by the electric oven is greater than the fuse of rating 5A and hence the fuse gets melts and hence circuit will get broken.
3.) What precautions should be taken to avoid the overloading of domestic electric circuit?
Ans:
Following are the precautions taken to avoid the overloading of domestic electric circuit:
- We don’t have to connect many electric appliances to a single socket and avoid to use them at same time also.
- The appliances having some faults or damage we have to not connect them in the circuit.
- And we have to use fuses of proper rating in series with the circuit which protect the whole circuit and also electric appliances.
- Also, we have to use earthing system so that we get protected from severe shock.
Exercise Solution
1.) Which of the following correctly describes the magnetic field near a long straight wire?
a) the field consist of straight lines perpendicular to wire
b) the field consist of straight lines parallel to the wire
c) the field consist of radial lines originating from the wire
d) the field consist of concentric circles centred on the wire.
Ans:
d) the field consist of concentric circles centred on the wire
2.) The phenomenon of electromagnetic induction is
a) the process of charging a body
b) the process of generating magnetic field due to current passing through a coil.
c) producing induced current in a coil due to relative motion between magnet and the coil
d) the process of rotating a coil of electric motor
Ans:
c) producing induced current in a coil due to relative motion between magnet and coil
3.) The device used for producing electric current is called a
a) generator
b) galvanometer
c) ammeter
d) motor
Ans:
a) generator
4.) The essential difference between an AC generator and a DC generator is that
a) AC generator has an electromagnet while a DC generator has permanent magnet
b) DC generator will generate a higher voltage
c) AC generator will generate a higher voltage
d) AC generator has slip rings while the DC generator has a commutator
Ans:
d) AC generator has slip rings while the DC generator has a commutator
5.) At the time of short circuit, the current in the circuit
a) reduces substantially
b) does not change
c) increase heavily
d) vary continuously
Ans: c) increase heavily
6.) State whether the following statement are true or false.
a) An electric motor converts mechanical energy into electrical energy.
Ans: False
Because electric motor converts electrical energy into mechanical energy.
b) An electric generator works on the principle of electromagnetic induction.
Ans: True
c) The field at the centre of a long circular coil carrying current will be parallel straight lines.
Ans: True
d) A wire with a green insulation is usually the live wire of an electric supply.
Ans: False
Because a wire with green insulation is usually a earth wire and wire with red insulation is the live wire.
7.) List two methods of producing magnetic field.
Ans:
The following are the methods of producing magnetic field:
- The straight conductor carrying current also produces magnetic field
- By using permanent magnet, we can also produce magnetic field.
- With the help of electromagnets, we can produce strong magnetic field also.
Alternative Answer –
1) Using current carrying coil we can produce magnetic field.
2) Using round magnet we can produce magnetic field.
8.) How does a solenoid behave like a magnet? Can you determine the north and south pole of a current carrying solenoid with the help of a bar magnet? Explain.
Ans:
- Solenoid is a coil consisting of large number of circular turns of insulated copper wire in the form of cylinder.
- The magnetic field lines generated around the solenoid is as shown in figure.
Fig. Magnetic field due to solenoid
- And the field produced due to solenoid is similar to the field produced due to the bar magnet.
- To identify the poles of the current carrying solenoid we bring the north pole of bar magnet near to the negative terminal of battery then it repels the magnet that mean the pole of solenoid connected to the negative terminal of battery is the north pole.
- Since like poles repels each other.
- In similar manner if we bring south pole of the bar magnet near to the positive terminal of the battery then it repels the bar magnet. Which means that the pole of the solenoid connected to the positive terminal of battery is the south pole. Since like poles repels each other.
- In this way we can identify the poles of the solenoid carrying current.
Alternative Answer –
A solenoid is a cylindrical object with insulated copper wire wrapped very close to the cylinder. If we observe the field lines of a solenoid when we let current flow in it, those field lines resemble a bar magnet. Thus, the solenoids magnetic field and magnetic field of bar magnet are similar to each other. As we all know that a magnet has two poles, one north and the other south. The north pole attracts the south pole and the north pole repels north pole of the magnet and south pole attracts north and south pole repels the south pole of the magnet. So when we try to put the north pole of the magnet inside the solenoid, if one pole of the solenoid attracts the magnet it is south pole of the solenoid. If the same pole of the solenoid repels the magnet,it will be the north pole of the solenoid.
In case you are missed :- Previous Chapter Solution
9.) When is the force experienced by current carrying conductor placed in magnetic field is largest?
Ans:
When the magnetic field direction and electric current through the current carrying conductor are perpendicular to each other then only maximum force is experienced by current carrying conductor placed in magnetic field.
Alternative Answer –
If the electric current and the direction of magnetic field are perpendicular to each other, then the force experienced by current carrying conductor placed in a magnetic field largest.
10.) Imagine that you are sitting in a chamber with your back to one wall. An electron beam moving horizontally from back wall towards the front wall, is deflected by strong magnetic field to your right side. What is the direction of magnetic field?
Ans:
- As the negatively charged electron beam is moving from back wall to front wall, hence current direction is opposite to the flow of electrons i.e. from front wall to back wall.
- Thus, according to Fleming’sleft-hand rule, the direction of magnetic field is vertically downward direction.
Alternative Answer –
By Fleming’s left hand rule.The direction of the magnetic field is vertically downwards.
The direction of current is front to back. And the direction of magnetic field is rightward. Therefore By Fleming’s left hand rule the direction of magnetic field is vertically downwards.
11.) Draw a labelled diagram of a electric motor. Explain its principle and working. What is the function of split ring in an electric motor?
Ans:
Principle:
- The principle of electric motor is based on the magnetic effect of electric current. According to which when a current carrying coil is placed in magnetic field then there will be force acting on the coil which rotates it. This is the principle of electric motor.
- Electric motor is a rotating device which converts electrical energy into mechanical energy. The figure shows the labelled diagram of simple electric motor.
Construction and Working:
Fig. 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.
- In commercial motors, field coils are used for producing magnetic field rather than a permanent magnet as in simple electric motor.
- In electric motor, split rings act as a commutator which reverse the direction of flow of current through the circuit. Due to reversing the current direction the magnetic force also gets reversed. And hence the coil is rotating continuously.
Alternative Answer –
Principle : An electric motor is an divice which contains rotating current carrying coil that converts electrical energy to machenical energy.
Working : When we close the switch in the circuit diagram the current will flow through the circuit ABCD. We notice that current flow through A to B and C to D, which are opposite to each other. When current flow through arm A to B then the direction of current is A to B, then we apply Fleming’s left hand rule for the direction of force then we notice that force acting on the arm AB pushes it downward and force acting on the arm CD pushes it upward at the same time and rotate anti clockwise after the half rotation the commutator reverses the direction of current flow. Commutator is a device which reverse the direction of current, in this experiment split ring act as a commutator. When current change its direction with the help of split ring, then it flow in the direction DCBA. The direction of current is D to C then the force acting on a arm DC pushes it downwards and the force acting on a arm BA pushes it upwards at a same time in clockwise direction, after the half rotation again commutator reverses the current and again the same process continues. Therefore we can say that coil rotates unidirectional.
Split ring is an commutator in which its work is to reverse the direction of current.
12.) Name some devices which uses electric motor.
Ans:
Electric motors are used in water pumps, electric fans, washing machines, electric mixers etc.
Alternative Answer –
- Pump – set (water pump)
- Mixer grinder.
- Microwave oven.
- Fan
13.) A wire of insulated copper wire is connected to a galvanometer. What will happen if a bar magnet is a) pushed into the coil b) withdrawn from inside the coil c) held stationary inside the coil.
Ans:
Given that, a coil of insulated copper wire is connected to a galvanometer.
a) Now if we push a bar magnet into coil then due to electromagnetic induction current is induced and hence galvanometer shows some deflection.
b) now if we withdraw the bar magnet from inside the coil then also current is induced but in reverse direction and galvanometer shows some deflection.
c) if we held the bar magnet stationary inside the coil then there will be no change in magnetic field and hence no current is induced due to which galvanometer shows no detection.
Alternative Answer –
(i) If a bar magnet pushes into the coil then the galvanometer deflection shows single direction or the needle of the galvanometer move momentarily in single direction.
(ii) If a bar magnet is withdrawn from inside the coil then the galvanometer deflection shows backward direction or the needle of the galvanometer move momentarily in opposite direction.
(iii) If a bar magnet is held stationary inside the coil then the galvanometer deflection shows no direction or zero deflection.
14.) Two circular coils A and B are placed close to each other. If the current in the coil A is changed, will some current be induced in coil B? Give reason.
Ans:
- Given that, two circular coils A and B are placed close to each other. If the current in the coil A is changed then the magnetic field around the coil A also changes due to which the magnetic field around the coil B also changes.
- This change in magnetic field around the coil B induces the current in the coil.
- This phenomenon of inducing electric current in a coil due to the change in current in the other coil, when they are placed close to each other is called as electromagnetic induction.
Alternative Answer –
Yes. If the current in the coil A is changed, then some current be induced in the coil B. Because w.k.t electronagetive induction it is a process in which producing induced current in a coil between magnet and the coil. Come to the question, if the current in coil A is changed, then the magnet field lines which are arround the coil A is changed then the magnetic field lines which are arround the coil B also changed because both coil are placed close to each other.
15.) State the rule to determine the direction of a
a) magnetic field produced around a straight conductor carrying current
b) force experienced by a current carrying straight conductor placed in magnetic field which is perpendicular to it and
c) current induced in a coil due to its rotation in magnetic field.
Ans:
a) By using Right hand thumb rule, we can determine the direction of magnetic field produced around a straight conductor carrying current.
b) By using Fleming’s left-hand rule, we can determine the direction of force experienced by a current carrying straight conductor placed in magnetic field which is perpendicular to it.
c) By using Fleming’s right-hand rule, we can find the direction of current induced in a coil due to its rotation in magnetic field.
Alternative Answer –
(i) Right hand thumb rule is used to determine the direction of a magnetic field produced around a straight conductor carrying current.
(ii) Fleming’s left hand rule is used to determine the direction of force experienced by a current carrying straight conductor placed in a magnetic field which is perpendicular to it.
(ii) Fleming’s right hand rule is used to determine the direction of current induced in a coil due to its rotation in a magnetic field.
16.) Explain the underlying principle and working of an electric generator by drawing a labelled diagram. What is the function of brushes?
Ans:
Principle:
- The electric generator works on the principle of electromagnetic induction. When a straight conductor is continuously moved in a string magnetic field then current is induced in the conductor.
- By using this phenomenon in electric generator, mechanical energy is used to rotate the conductor in a magnetic field to produce electricity.
Construction and working:
Fig. Electric Generator
- 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.
- 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 are attached internally to this ring. 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 unidirectional 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 unidirectional current flows called as DC current like in an electric motor.
Alternative Answer –
Principle: The working principle of electric generator is depend on electromagnetic induction phenomenon. An process in which producing induced current in a coil between magnet and the coil whose direction given by the Fleming’s right hand rule.
Working : In the figure we notice that the brush B1 is pressed with the ring R1 and the brush B2 is pressed with the ring R2 when current flow through the when attached axel is rotate which is connected with two rings, magnetic field will be produced then the arm AB move upwards and the arm BC move downwards and rotate in clock wise direction by the Fleming’s right hand rule the induced current are set up in the arms along the direction AB and CD, after half rotation the generated current will flow reverse direction DCBA , then the direction of current is D to C, then the arm DC move upwards and the arm BA move downwards and it rotate anti clock wise direction, therefore by Fleming’s right hand rule the direction of induced current in these arms change, and again after half rotation the current will change its direction and an alternative current is produced from the generator.
Function of brushes : These brushes which are present in outer end,are connected to galvanometer to show the flow of current in the given external circuit which we can see in the form of deflection in galvanometer , these brushes transfer the current from internal circuit to extranal circuit.
17.) When does an electric short circuit occurs?
Ans:
When live wire and neutral wire comes in contact due to the damage in insulation of wires or some defects in the electrical equipment. And as a result, the current increases through the circuit due to which short circuit occurs.
Alternative Answer –
If insulated wire is damaged inside the circuit, when current flow through the circuit the live wire and neutral wire directly come in the contact, in this stage the current will increases its strength, the circuit is not able to handle this increase in strength of current. In this stage electric short circuit is occurs.
18.) What is the function of earth wire? Why is it necessary to earth metallic appliances?
Ans:
- The earth wire which is having green insulation is connected to the metal plate which is deep under the ground or in earth near our house.
- Earth wire is used as safety measure for the metallic appliances such as electric press, toaster, table fan, refrigerator etc.
- Because in this case, the metallic body is directly connected to earth wire which is providing low resistance path for the current flowing through it. In this way, it keeps its potential to that if the earth by ensuring the leakage of current to the metallic body of appliances due to which we get protected from severe electric shock.
- Because of this reason earth wire is necessary to earth metallic appliances.
Alternative Answer –
When the earth wire is installed in the house, if there is a thunderstorm and something disturbs the home electrical system, it can be prevented by the earth wire system. Sometimes, lightning strikes the house electric system and damages the house electrical equipment which can be avoided by the earth wire system. And,can prevent leakage in electrical current and transfer the leakage to ground. Therefore the earth metallic appliances is necessary .
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