NCERT Exemplar Solution Class 10 Science Chapter 13
NCERT Exemplar Solution Class 10 Science Chapter 13 Magnetic Effects of Electric Current all Questions Answer Solution. NCERT Exemplar Class 10 Science Chapter 13 Solution PDF.
NCERT Exemplar Solution Class 10 Science Chapter 13: Overview
NCERT Exemplar Solution Class 10 Science Chapter 13 |
|
Board |
NCERT |
Topic |
Exemplar Problem Solution |
Class |
10 |
Subject |
Science |
Chapter |
13 |
Chapter Name |
Magnetic Effects of Electric Current |
NCERT Exemplar Solution Class 10 Science Chapter 13 Magnetic Effects of Electric Current
Chapter 13
Magnetic Effects of Electric Current
Multiple Choice Questions
1) Choose the incorrect statement from the following regarding magnetic lines of field
(a) The direction of magnetic field at a point is taken to be the direction in which the north pole of a magnetic compass needle points
(b) Magnetic field lines are closed curves
(c) If magnetic field lines are parallel and equidistant, they represent zero field strength
(d) Relative strength of magnetic field is shown by the degree of closeness of the field lines
Ans🙁c) If magnetic field lines are parallel and equidistant, they represent zero field strength
Since the magnetic lines of force are in the form of continuous loop, due to which the strength of magnetic field at every point on lines is different.
Now, if the magnetic field lines are parallel and equidistant then there will be uniform magnetic field, representing constant magnetic field strength at each point on the lines of force.
2) If the key in the arrangement (Figure 13.1) is taken out (the circuit is made open) and magnetic field lines are drawn over the horizontal plane ABCD, the lines are
(a) Concentric circles
(B) Elliptical in shape
(c) Straight lines parallel to each other
(d) Concentric circles near the point O but of elliptical shapes as we go away from it
Ans:(c) straight lines parallel to each other
We know that, the changing current through the coil induces a magnetic field around it.
Here, if we removed the key then circuit becomes open and no current flows through it and hence no magnetic field is induced. Then the magnetic field lines are only due to the earth’s magnetic field and which are straight lines parallel to each other.
3) A circular loop placed in a plane perpendicular to the plane of paper carries a current when the key is ON. The current as seen from points A and B (in the plane of paper and on the axis of the coil) is anti-clockwise and clockwise respectively. The magnetic field lines point from B to A. The N-pole of the resultant magnet is on the face close to
(a) A
(b) B
c) A if the current is small, and B if the current is large
(d) B if the current is small and A if the current is large
Ans: (a) A
Because magnetic lines of force are originating from North Pole and ends on South Pole.
Here, magnetic field lines point from B to A.
4) For a current in a long straight solenoid N- and S-poles are created at the two ends. Among the following statements, the incorrect statement is
(a) The field lines inside the solenoid are in the form of straight lines which indicates that the magnetic field is the same at all points inside the solenoid
(b) The strong magnetic field produced inside the solenoid can be used to magnetize a piece of magnetic material like soft iron, when placed inside the coil
(c) The pattern of the magnetic field associated with the solenoid is different from the pattern of the magnetic field around a bar magnet
(d) The N- and S-poles exchange position when the direction of current through the solenoid is reversed
Ans: (c) The pattern of the magnetic field associated with the solenoid is different from the pattern of the magnetic field around a bar magnet
Because, the pattern of the magnetic field associated with the solenoid is same as the pattern of magnetic field lines around a bar magnet.
5) A uniform magnetic field exists in the plane of paper pointing from left to right as shown in Figure 13.3. In the field an electron and a proton move as shown. The electron and the proton experience
(a) Forces both pointing into the plane of paper
(b) Forces both pointing out of the plane of paper
(c) Forces pointing into the plane of paper and out of the plane of paper, respectively
(d) Force pointing opposite and along the direction of the uniform magnetic field respectively
Ans: (a) forces both pointing into the plane of paper
In fig. the direction of motion of proton and neutron is opposite to each other but perpendicular to the direction of magnetic field. As we know that current flows in the opposite direction of the direction of motion of electrons. And hence, here the direction of current due to proton and neutron is same. By Fleming’s left hand rule, the forces experienced by proton and neutron are both pointing into the plane of paper.
6) Commercial electric motors do not use
(a) An electromagnet to rotate the armature
(b) Effectively large number of turns of conducting wire in the current carrying coil
(c) A permanent magnet to rotate the armature
(d) A soft iron core on which the coil is wound
Ans: (c) a permanent magnet to rotate the armature
Because in simple electric motor permanent electromagnets are used while in commercial motors instead of permanent electromagnet only electromagnets are used which is the main point of difference in them.
7) In the arrangement shown in Figure 13.4 there are two coils wound on a non-conducting cylindrical rod. Initially the key is not inserted. Then the key is inserted and later removed. Then
(a) The deflection in the galvanometer remains zero throughout
(b) There is a momentary deflection in the galvanometer but it dies out shortly and there is no effect when the key is removed
(c) There are momentary galvanometer deflections that die out shortly; the deflections are in the same direction
(d) There are momentary galvanometer deflections that die out shortly; the deflections are in opposite directions
Ans: (d) there are momentary galvanometer deflections that die out shortly; the deflections are in opposite directions
When key is inserted galvanometer shows small deflection and when key is removed then it shows deflection in opposite direction, and this are momentary galvanometer deflections which die out shortly. Since the two coils are wound on non-conducting cylindrical rod.
8) Choose the incorrect statement
(a) Fleming’s right-hand rule is a simple rule to know the direction of induced current
(b) The right-hand thumb rule is used to find the direction of magnetic fields due to current carrying conductors
(c) The difference between the direct and alternating currents is that the direct current always flows in one direction, whereas the alternating current reverses its direction periodically
(d) In India, the AC changes direction after every 1/50 second
Ans: (d) In India, the AC changes direction after every 1/50 second
In India the frequency of AC current is 50 Hz, and it changes its direction 2 times in one cycle.
2 * 50 =100 times in 1 second.
Thus, AC used in India changes its direction 100 times in 1 second.
9) A constant current flows in a horizontal wire in the plane of the paper from east to west as shown in Figure 13.5. The direction of magnetic field at a point will be north to South
(a) Directly above the wire
(b) Directly below the wire
(c) At a point located in the plane of the paper, on the north side of the wire
(d) At a point located in the plane of the paper, on the south side of the wire
Ans: (b) Directly below the wire
By right hand thumb rule, the outstretched thumb gives the direction of current and the curled fingers gives the direction of magnetic field. Here, the current flows from east to west in the plane of paper, hence direction of magnetic field at a point will be north to south directly below the wire.
10) The strength of magnetic field inside a long current carrying straight solenoid is
(a) More at the ends than at the center
(b) Minimum in the middle
(c) Same at all points
(d) Found to increase from one end to the other
Ans: (c) Same at all points
Because, inside the solenoid the magnetic lines of force are straight and parallel to each other which represents the uniform magnetic field. And hence, the strength of magnetic field at all points is same.
11) To convert an AC generator into DC generator
(a) split-ring type commentator must be used
(b) Slip rings and brushes must be used
(c) A stronger magnetic field has to be used
(d) A rectangular wire loop has to be used
Ans: (a) split-ring type commentator must be used
To produce a uni directional DC current we have to use a split ring type of commutator, due to which the 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.
12) the most important safety method used for protecting home appliances from short circuiting or overloading is
(A) earthling
(b) Use of fuse
(c) Use of stabilizers
(d) Use of electric meter
Ans: (b) Use of fuse
Fuse wire is a safety device connected in series in electrical circuits to protect the circuit from the extra current flow. The rating of the fuse wires is fixed. When the extra current greater than the rating flows through the circuit, due to which fuse get heated and meals to break the circuit and protect the electrical appliances from damaging.
Short Answer Questions
13) A magnetic compass needle is placed in the plane of paper near point A as shown in Figure 13.6. In which plane should a straight current carrying conductor be placed so that it passes through A and there is no change in the deflection of the compass? Under what condition is the deflection maximum and why?
Ans:
As we know that, by right hand thumb rule, the magnetic field and current direction are perpendicular to each other. If we stretched out the right hand thumb and curled fingers around it, then thumb gives the direction of current and curled fingers gives the direction of magnetic field which are perpendicular to each other. If a magnetic compass needle is placed in the plane of a paper near to point A as in figure then to have no change in deflection of the compass, we should place a straight current carrying conductor which passes through A and in the plane of paper. Because when a conductor is placed in the plane of paper there is no magnetic force acting on the compass and hence it does not show any deflection.
For maximum deflection of a compass there should be a maximum magnetic force should be acts on it. This happen only when conductor is placed perpendicular to the plane of paper. When it is placed perpendicular to plane of paper maximum magnetic force acts on it, due to which it gets more deflected
14) Under what conditions permanent electromagnet is obtained if a current carrying solenoid is used? Support your answer with the help of a labelled circuit diagram.
Ans:
Fig.14
Solenoid is a cylindrical shaped closely wrapped coil by the wire of many number of circular turns of insulated copper wire. When the current is passed through the solenoid, the magnetic field is generated around it which has similar nature like the magnetic field around the bar magnet. In fact the magnetic field generated around the solenoid creates magnetic poles due to which one pole of solenoid act as North Pole and other as a South Pole. Inside the solenoid the magnetic field lines are straight and parallel to each other, which indicates that at all points inside a solenoid magnetic field is constant forming the uniform magnetic field inside the solenoid.
When the ferromagnetic materials are placed inside the solenoid then the metal produces strong magnetic field around solenoid and hence it get permanently magnetized and act as a permanent electromagnet.
Ferromagnetic materials are the materials having permanent magnetism and magnetic susceptibility is high, due to which even after removal of magnetic field they don’t loses their magnetization and hence get permanently magnetized. Because of this reason they are used for producing permanent electromagnet.
The above figure14 shows the current carrying solenoid coil is used to produce permanent electromagnets.
15) AB is a current carrying conductor in the plane of the paper as shown in Figure 13.7. What are the directions of magnetic fields produced by it at points P and Q? Given r1 > r2, where will the strength of the magnetic field be larger?
Ans:
According to the right hand thumb rule, if right hand thumb outstretched upward and fingers are curled around it, then upward thumb’s direction is the direction of electric current and curled finger gives the direction of magnetic field. Hence we conclude that from figure, the upward direction is current direction and the downward and the magnetic field direction is anticlockwise direction.
AB is a current carrying conductor in the plane of paper as shown in figure. From right hand thumb rule discussed above, we conclude that the direction of magnetic field at point P is into the plane of paper and direction of magnetic field at point Q is out of the plane of paper.
The strength of magnetic field depends on the distance of the conductor from the point at which the magnetic field strength have to be measured.
The magnetic field strength is inversely proportional to the distance of the conductor from the point at which magnetic field have to be measured. Hence the larger the distance smaller the strength of the magnetic field.
Given that r1 >r2, hence at point P magnetic field strength is lower and at a point Q it is larger than at P.
16) A magnetic compass shows a deflection when placed near a current carrying wire. How will the deflection of the compass get affected if the current in the wire is increased? Support your answer with a reason.
Ans: A magnetic compass shows a deflection when placed near a current carrying wire, because the strength of magnetic field depends on the current flowing through the wire. And hence, the magnetic field is directly proportional to the current. If the current is increased, then magnetic field also increases due to which the magnetic compass shows more deflection.
17) It is established that an electric current through a metallic conductor produces a magnetic field around it. Is there a similar magnetic field produced around a thin beam of moving (i) alpha particles, (ii) neutrons? Justify your answer.
Ans: We know that, an electric current through a metallic conductor produces a magnetic field around it that is electric current through a conductor is responsible for magnetic field produced. In case of alpha particles, alpha particles are the positive charge nuclei identical to the nucleus of helium -4 atom. They are having +2 charge.
And magnetic field is produced only around the beam of moving particles having charge. Hence the thin beam of moving alpha particle produces an electric current in the direction of motion of alpha particles and due to which they produces the magnetic field also.
But in case of neutrons, neutrons are the neutral charged particle that is neutrons have no charge and hence does not constitute any type of current and hence does not produce any kind of magnetic field.
18) What does the direction of thumb indicate in the right-hand thumb rule? In what way this rule is different from Fleming’s left-hand rule?
Ans:
Fig. 18 a) Right hand thumb rule
The right hand thumb rule and Fleming’s left hand thumb rule both are connected to magnetic effects of electric current. But they have smaller difference. According to right hand thumb rule, when a right hand’s thumb is out stretched in upward direction and fingers are curled around it, then the direction of thumb gives the direction of current and the curled finger gives the direction of magnetic field.
Fig. 18 b) Fleming’s left hand rule
According to Fleming’s left hand thumb rule, when we put a current carrying conductor inside the external magnetic field it produces a force which is proportional to magnetic field and direction of current also.
Thus right hand thumb in right hand thumb rule indicates the direction of current which is surrounded by magnetic field and left hand thumb in Fleming’s left hand rule indicate the direction of force experienced by a conductor when placed in an external magnetic field.
19) Mena draws magnetic field lines of field close to the axis of a current carrying circular loop. As she moves away from the center of the circular loop she observes that the lines keep on diverging. How will you explain her observation?
Ans:
Fig.19 magnetic field lines produced by current carrying circular loop
When a current is passed through a circular loop of wire, the magnetic lines of forces are produced in the form of concentric circles with the center is the point at which the wire passes through the board. The magnetic field concentration or strength is more at the center of the concentric circles formed. The magnetic field lines representing circular concentric loops looks like a straight lines near the center of the concentric circles.
And this concentric circles become larger and larger as we move away from their centers. Because the magnetic field strength decreases as we go away from the current carrying conductor and hence if distance is increased strength of the magnetic field decreases.
Thus, Meena is moving away from the center of the circular loop that is distance from the current carrying conductor is increased due to which magnetic field strength is decreased and because of this she observed that the lines keep on diversing.
20) What does the divergence of magnetic field lines near the ends of a current carrying straight solenoid indicate?
Ans:
Fig.20 magnetic lines formed in a solenoid
Solenoid is a coil wrapped by insulated copper wire of number of circular windings in a cylindrical shape. The one end of the solenoid behaves as North Pole and other as South Pole. When a current is passed through it, it produces a magnetic field as shown in figure. The magnetic field lines inside the solenoid are like a parallel straight lines which shows the presence of same magnetic field at all points inside the solenoid.
As we see, at the ends of solenoid the magnetic field lines are decreasing or diverging outside. This is because the magnetic field is inversely proportional to the distance from the conductor. As we go away from the conductor distance from the conductor increases and hence magnetic field strength decreases.
Thus, the degree of closeness of the field lines shows the strength of magnetic field. Thus, the divergence of magnetic field lines near the ends of a current carrying solenoid indicates the decrease in magnetic field at the ends of solenoid.
21) Name four appliances wherein an electric motor, a rotating device that converts electrical energy to mechanical energy, is used as an important component. In what respect motors are different from generators?
Ans: Vacuum cleaners, electric fans, washing machines, air conditioners, grinders mixers, refrigerators, computers, MP3 players etc. are the the domestic appliances where in an electric motor which is a rotating device that convert electrical energy to mechanical energy is used an important component.
The electric motor is an electronic device which converts electrical energy into mechanical energy. It works on the principle that, when a current carrying conductor is placed in a magnetic field, it experiences a force or torque.
The generators are used to convert the mechanical energy into electrical energy. The main difference between an electric motor and a generator is that, electric motor convert electrical energy to mechanical energy whereas the generators converts mechanical energy into electrical energy.
22) What is the role of the two conducting stationary brushes in a simple electric motor?
Ans: The role of two stationary brushes in a simple electric motor is to receive the current from the source battery and two flow back it to the battery again. Because it is connected to the conducting edges through halves of split ring whose inner sides are insulated and connected to axle.
23) What is the difference between a direct current and an alternating current? How many times does AC used in India change direction in one second?
Ans: A) In DC current charge flows only in one direction and hence it is also called as uni-directional current.
B) Frequency of DC current is zero. The magnitude of DC current is fixed or constant. DC circuit possesses mostly register only.
C) The power factor for DC circuits is always 1.
D) In DC circuits there is a high energy losses.
DC circuits are not used for long distance transmission because of high energy losses.
Fig.23 a) DC current
A) 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.
B) In India frequency of AC is 50 Hz.
C) The magnitude of AC current is varying with time.
D) AC circuit possesses registers, capacitors and inductors also.
E) The power factor for AC circuit is lies between 0 and 1.
There are low energy losses for AC circuits.
Fig.23 b) AC current
A) AC circuits are used for long distance transmission because of low energy losses.
B) In India the frequency of AC current is 50 Hz, and it changes its direction 2 times in one cycle.
2 * 50 =100 times in 1 second.
Thus, AC used in India changes its direction 100 times in 1 second.
24) What is the role of fuse, used in series with any electrical appliance? Why should a fuse with defined rating not be replaced by one with a larger rating?
Ans: Fuse wire is a safety device connected in series in electrical circuits to protect the circuit from the extra current flow. The rating of the fuse wires is fixed. When the extra current greater than the rating flows through the circuit, due to which fuse get heated and meals to break the circuit and protect the electrical appliances from damaging.
The fuse wire are having specific melting point, if temperature is increased than melting point of fuses then they get melts thereby protecting the circuits. The fuses are connected in series to the main source and they are having fixed rating.
We have to connect the fuse of required rating in a circuit according to the current required. The fuse of 10A rating shall pass 10A current only and if current exceeds, it get heated and melts thereby protecting the electrical appliances.
If we used the fuses of rating greater than required rating then it allows the extra current which will damage the electrical appliances. Because of this reason, the fuse with defined rating should not be replaced by one with the larger rating.
Long Answer Questions
25) Why does a magnetic compass needle pointing North and South in the absence of a nearby magnet get deflected when a bar magnet or a current carrying loop is brought near it. Describe some salient features of magnetic lines of field concept.
Ans: We know that, when a bar magnet is brought near to a coil, the magnetic field around it changes and current is induced in the coil and vice versa. The magnetic compass needle points North and South in the absence of a nearby magnet because the magnetic force acting on it is only due to to earth’s magnetic field.
And the compass needle shows deflection when a current carrying coil brought near to it because the current through the coil produces a magnetic field and hence total force acting on the compass needle is due to the superposition of earth’s magnetic field and magnetic field due to current carrying coil.
The silent features of magnetic lines of force are as follows:
A) The magnetic field lines are directed from South to North Pole inside the magnet.
B) Magnetic field lines are the closed curves.
C) The magnetic field strength is stronger where the magnetic field lines are crowded and it becomes weaker where the magnetic field lines are more distant apart.
D) It is found that no two field lines cross each other.
E) Field lines are in the form of continuous loops and tangent at any point on the field line gives the direction of magnetic field at that point.
26) With the help of a labelled circuit diagram illustrate the pattern of field lines of the magnetic field around a current carrying straight long conducting wire. How is the right hand thumb rule useful to find direction of magnetic field associated with a current carrying conductor?
Ans: The above figure illustrate the pattern of magnetic field lines around a current carrying straight long conducting wire. When the current is passed through the straight conductor the magnetic field lines in the form of concentric circles are generated, whose centers are on the wire as shown in figure.
If the direction of current is downward then the magnetic field lines direction is clockwise as shown in figure.
The direction of magnetic field lines produced is given by right hand thumb rule clearly.
Fig.26
According to right hand thumb rule, when the thumb of right hand is stretched out in upward direction and fingers are curled around it and if the thumb gives direction of current then the curled finger gives the direction of magnetic field produced.
If the direction of current is reversed then the direction of magnetic field lines also get reversed.
27) Explain with the help of a labelled diagram the distribution of magnetic field due to a current through a circular loop. Why is it that if a current carrying coil has n turns the field produced at any point is n times as large as that produced by a single turn?
Ans: When a current is passed through a circular loop of wire, the magnetic lines of forces are produced in the form of concentric circles with the center is the point at which the wire passes through the board.
The magnetic field concentration or strength is more at the center of the concentric circles formed. The magnetic field lines representing circular concentric loops looks like a straight lines near the center of the concentric circles.
And this concentric circles become larger and larger as we move away from their centers. Because the magnetic field strength decreases as we go away from the current carrying conductor and hence if distance is increased strength of the magnetic field decreases.
The magnetic field produced due to a current through a circular loop depends on the current passing through the circular loop and on the number of turns of current carrying coil. If the number of turns of a current carrying coil are increased by n then current through it also increases n times and hence the magnetic field produced will be n times as large as produced by single turn.
Because the direction of current flowing through each turn is same due to which the total current is the sum of all currents through n turns. Hence current adds up if number of n turns are increased and hence magnetic field produced is also increases.
28) Describe the activity that shows that a current-carrying conductor experiences a force perpendicular to its length and the external magnetic field. How does Fleming’s left-hand rule help us to find the direction of the force acting on the current carrying conductor?
Ans:
Fig.28
We know that an electric current flowing through a conductor produces a magnetic field which exerts a force on a magnet placed near to a conductor. French scientist Andre Marie Ampere suggested that, the magnet also exert an equal and opposite force on that conductor. The force acting on a current carrying conductor due to magnetic field is illustrated by using following activity.
A small aluminum rod PQ is suspended horizontally from a stand by using a connecting wires at two ends as shown in figure. We have placed a strong horse shoe magnet such that the rod lies between the two poles and we have placed the north pole of a magnet vertically below, South pole will be placed vertically above the aluminum rod so that magnetic field is directed upwards.
We have connected the aluminum rod in a series with the battery, a key and rheostat as shown in figure and current is passed through aluminum rod from Q to end P. It is observed that the aluminum rod get deflected towards left.
If we reverse the direction of current then the rod will be displaced towards right. The displacement of rod is due to the force exerted on the current carrying aluminum rod when it is placed in a magnetic field. And hence it is observed that the direction of force acting on a conductor concludes that, it depends on the current through conductor and the direction of magnetic field.
And it is observed that, the rod get displaced through maximum distance when current direction and magnetic field direction are perpendicular to each other. This can be explained by using Fleming’s left hand rule. According to flaming left hand rule, when a current carrying straight conductor is placed in an external magnetic field, then the conductor experiences a force which is perpendicular to the direction of current and magnetic field also.
This gives the direction of magnetic force. When we held left hand in a way that thumb, first finger and second finger are mutually perpendicular to each other, then the thumb gives the direction of force, first finger gives the direction of magnetic field and second finger gives the direction of current which is shown in figure below.
In this way Fleming’s left hand rule help us to find the direction of the force acting on the current carrying conductor.
29) Draw a labelled circuit diagram of a simple electric motor and explain its working. In what way these simple electric motors are different from commercial motors?
Ans:
Fig.29Simple 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. 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.
The commercial electric motor the uses an electromagnet instead of permanent magnet, large number of turns of the conducting wire in the current carrying coil and a soft iron core where the coil is wound, which enhances the power of the motor.
30) Explain the phenomenon of electromagnetic induction. Describe an experiment to show that a current is set up in a closed loop when an external magnetic field passing through the loop increases or decreases.
Ans: The phenomenon of electromagnetic induction is observed, when the magnetic field around the coil is changing then a potential difference is developed across it which conducts current inside it.
On the other hand when we take two coils and current is passed through the first coil it changed then magnetic field due to first coil also changes. Due to which magnetic field of second coil changes which produces a potential difference and current is flowing through second coil also. This phenomenon of inducing potential difference i.e. current by changing magnetic field and vice versa is called as electromagnetic induction.
Fig. 30
This was explained by Michael Faraday. To describe an experiment to show that, a current is set up in a closed loop when an external magnetic field passing through loop increased or decreased, consider the following experiment.
We have taken a coil of wire with many turns and its two ends are connected to galvanometer as shown in figure. When we move the north pole of a strong bar magnet towards the coil the galvanometer shows deflection to the right side. The deflection means there will be current produced in the coil. If we stop the moving magnet then galvanometer shows zero deflection in it.
Now if we have taken away the north pole of the magnet from coil then galvanometer shows deflection to left means current is produced in a coil.
Now we made the bar magnet stationary and coil is moved towards the north pole of a bar magnet then it is observed that, galvanometer shows deflection to right and if coil is moved away from the North Pole then galvanometer shows deflection to left side.
And further if we made both coil and magnet stationary then there will be no deflection. From this experiment it is clear that the change in magnetic field induces current in a coil and also changing current in a coil produces a magnetic field, this phenomenon is called as electromagnetic induction.
31) Describe the working of an AC generator with the help of a labelled circuit diagram. What changes must be made in the arrangement to convert it to a DC 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. 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 the 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.
32) Draw an appropriate schematic diagram showing common domestic circuits and discuss the importance of fuse. Why is it that a burnt out fuse should be replaced by another fuse of identical rating?
Ans:
Fig.32 Common domestic circuit
A fuse is an electronic safety device used to protect the home electrical appliances from short-circuiting.
The fuses are having fixed rating. The fuses are connected in a series with the electrical circuit. The electrical appliances requires a particular amount of current, to provide that amount of current we should use fuses.
For the appliances like refrigerator, coolers the fuses of high rating requires while for bulbs, fans fuses of low rating will requires. Because if a large current is provided to the home appliances then short circuit will happen and which damage the whole circuit. To avoid this, we use fuses.
When the extra current flows through the circuit the fuse of particular rating used get heated and melts, which breaks the circuit and thereby protects from damaging the electrical appliances. The fuse are made of particular metals and having specific melting point.
Fuses performs most important role in an electric circuit. If the fuse of particular rating is burn out then we should replace that fuse by another fuse of same rating because if the rating of fuse is increased then it allows extra current which would be provided to electrical appliances and there will be damage of that appliances.
To avoid this type of damage we should replace the fuse by the same fuse rating.