Class 10 Physics: Chapter 03 Electro-Magnetic Induction- Questions and Answers
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Class 10 Physics Questions and Answers - Chapter 03 Electro-Magnetic Induction
1. What is electromagnetic Induction?
16. What is self-induction?
a) What do the parts X, A represent in the figure.
- Whenever there is a change in the magnetic flux linked with the coil, electricity is induced in the coil. This phenomenon is electromagnetic induction
*The current induced is the induced current,
*The voltage induced is the induced emf
2. What are the factors affecting the induced current?
- The number turns of the coil, Strength of the magnet, Speed of the magnet or solenoid
3. What is meant by direct current(DC)
- Current flows only in one direction
4. What is alternating current(AC)
- If the direction of current changes at regular intervals of time. It is an alternating current
5. What is the Generator?
- The generator is a device that makes use of electromagnetic induction. It converts mechanical energy into electrical energy
6. Which are the parts of an AC generator
- Armature, Brushes, Slip rings, Field Magnet
7. What is the frequency of AC
- The number of cycles per second is the frequency of AC
8. How much is the frequency of AC used for distribution in India?
- 50 Hz
9. When 50 Hz Ac is used, how many times will the direction of current change?
- 100
10. In AC generator Which part is kept stationary. Why?
- Armature is kept stationary and field magnet is allowed to rotate. The Armature is too heavy to rotate. This helps to eliminate the graphite brushes
11. Which are the parts of a DC Generator?
Field magnet, Armature, Brushes, Split rings
12. What are the similarities between DC motor and a DC Generator?
Both have a permanent magnet, Armature, Split ring commutator, Brushes
13. What is a period?
The time taken by the armature coil for a full rotation is called the period, T. Time is taken for half rotation (180⁰) is T/2
14.What is mutual induction?
- Consider two coils of wire kept side by side. When the strength or direction of the current in one coil changes, the magnetic flux around it changes. As a result, an emf is induced in the secondary coil. This phenomenon is mutual Induction.
- The coil into which we give current for the production of a magnetic field is the primary coil and the coil in which induced emf generated is the secondary coil
15.Which is the device based on the principle of mutual induction?
- Transformer
16. Comparison between a step-up transformer and step down transformer
17. Write formulas related to a transformer
16. What is self-induction?
- The change in the magnetic flux due to the flow of an AC (current) in a solenoid will generate a back emf in the same solenoid in a direction opposite to that applied to it This phenomenon is known as the self-induction.
*An inductor is is an insulated copper wire wound in a helical shape. They reduce the current in a circuit
17. Inductors are used in AC circuits. What is the reason?
- To regulate current without loss of power.
*Resistors cannot be used instead of inductors because energy (current) wasted in the form of heat
18. Inductors are not used in DC circuits Why?
- There is no change in a magnetic field and no induced emf forms. So no back emf. No self Induction occurs
19. Parts of moving coil microphone
- Voice coil, diaphragm, Permanent magnet
20. Working principle of Moving coil microphone
- Electromagnetic Induction
21. What is the energy transformation in a moving coil microphone?
Mechanical energy is converted into electrical energy
*Working of moving coil microphone
The voice coil is situated in a magnetic field. The diaphragm connected to the voice coil vibrates in accordance with the sound waves falling on it. As a result, electricals signals corresponding to the sound waves are generated the voice coil.
22. Which are the devices that worked on the principle of electromagnetic induction?
- Generator, moving coil microphone, transformer(mutual induction)
23. What are the power stations?
- Power stations are places where electricity is generated in large scale. Three-phase AC generators are used in power stations.
24. At what voltage current is produced in power stations?:
- 11KV(11000V)
25. What is the voltage for household purposes?
- 230V
26.What is the voltage needed for industrial purposes?
- 400V
27. What is the method to reduce transmission loss?
- Transmission of current at high voltage
28. Which type of transformer is there in a power station?
- Step-up transformer
29. Which type of transformer is a distribution transformer?
- Step down transformer
30. What is the potential of the neutral line?
- Zero
*The potential difference between a phase and a neutral is 230V
*The potential difference between any two-phase is 400V
31. To which device the electric line reaching home connected first
Kilowatt-hour meter. (Watt-hour meter)It is used to measure the electrical energy consumed.
Unit of electrical energy-Kilowatt hour
32.In which lines are the fuses connected?
- Phase line
*Main Switch: It is used to switch off the electric supply. It is connected in between fuse and ELCB
*In wiring red colour is used for phase line, black for neutral, green for the earth.
*In three-pin socket earth wire is connected to the larger pin.
33.How are the household devices connected ?:
- Parallel
34. What are the advantages of connecting devices in parallel
Devices work according to the marked power, Devices can be controlled using switches,
Effective resistance is low, All devices get an equal voltage
35. What is MCB?
- It is used instead of fuse wire. It automatically breaks the circuit if the excess flow of current in the circuit.
36. What is ELCB?
- It helps to break the circuit when there is a current leak
*In three-pin plug, earth pin is connected to the body of the device
*First Aids for an electric shock: Raise the temperature of the body by massaging, Give artificial respiration, Start first aid for the heart, Take the person to the hospital
37. The figure of a generator is given below.
b) What is the energy change occurs in such a device
c) What is the use of part Y in the figure
Answer.
a) X-slip ring, A-armature
b) Mechanical energy changes to electrical energy
c) supply electrical energy to an external circuit
38. The figure shows a resister, galvanometer connected to a 6V battery.
b) in which direction does the galvanometer needle deflect.
c) If the battery is replaced by an AC source, what change may be observed in the deflection of galvanometer needle? Why?
Answer:
a) series combination
b) single direction only
c) direction reverses continuously
39. In our country the frequency of AC produced for transmission is 50Hz.
a) What does it mean by frequency of an AC?
b)In one second, how many times the direction of emf change?
Answer:
a) number of cycles in one second
b) 50 times
40. Observe the figures a,b,c is given below and answer the questions (Solenoid, Bar magnet and galvanometer)
b) What will be the change in deflection of the galvanometer if the magnet in b &c circuits gets into the solenoid.
Answer:
a) a
b) galvanometer needle in-circuit b deflects in opposite direction to deflection of galvanometer needle in-circuit c
41. An armature coil of an AC generator when moved in the magnetic field, an induced current is produced.
a) Which is the law that helps to find the direction of current.
b) As per the law what does the forefinger represent?
Answer:
a) Flemings right-hand rule
b) Magnetic field
42. Whenever a change occurs to the magnetic flux connected to a closed circuit, a current is induced.
a) What is this phenomenon known as?
b) Name an instrument that works based on this principle.
Answer:
a) electromagnetic induction
b) Microphone/generator
43. Find out the correct statement/statements from those given below.
a) when a magnet is moved close to a solenoid, the magnetic flux linked with the solenoid will decrease.
b) when a magnet is moved close to a solenoid, the magnetic linked with the solenoid will increase.
c) when a magnet is moved close to a solenoid, the magnetic flux linked with the solenoid remains the same
Answer:
when a magnet is moved close to a solenoid, the magnetic linked with the solenoid will increase.
44. Correct error in the underlined part of the following statements if any
a) To complete one cycle of an AC, an armature needed to rotate 360⁰.
b) if the frequency of an AC is 50Hz, the armature completes 25 cycles per second
c) In an AC generator, current reverses direction in each half rotation
Answer:
b) AC of frequency is 50Hz has 50 cycles per second
c) In an AC generator, electric current flows in one direction for the first half rotation and reverses direction in the next half 45. A transformer has 10000 turns and 240V, 0.2A in the primary coil. If the current through the secondary coil is 0.4A.
a) What kind of transformer is this?
b) Find out the voltage and number of turns in the secondary coil.
c) Calculate maximum power in the secondary coil of this transformer.
Answer:
b) Vp x Ip = Vs x Is , Vs = 240 x 0.2 / 0.4 = 120 V
Vs/Vp = Ns/Np 120/240 = Ns/ 10000 Ns = 120 x 10000 / 240 = 50000 nos
c) P = VI = 240 x 0.2 = 48 W
46. Given below is the figure of a transformer
b) why thick coil is used in the secondary of the transformer.
Answer:
a. stepdown transformer
b. secondary current increases
47. Find out the odd one and Justify your answer.
Microphone, loudspeaker, Transformer, Generator,
Answer:
loudspeaker. All other devices works based on electromagnetic induction
48. By increasing diameter of conductors, transmission loss could be reduced.
a) What are the difficulties that arise if thick wires used as transmission lines
b)Suggest another method to reduce transmission loss.
Answer:
a. if thickness increases, weight increases, more supporting beams are required and expense increases
b. decrease current by increasing voltage
49. Identify the relation in the first pair and complete the following
Electromagnetic induction: Moving coil microphone
Mutual Induction:..............................
Answer: transformer
50. The number of turns in the primary of a transformer is two times greater than that in the secondary, then
a) identify the type of transformer?
b) If 50V is given to the primary, What will be the voltage obtained in the secondary?
c) If the current in its primary coil is 4A What will be the current in the secondary?
Answer:
a. step up transformer
b. 50 x 2 = 100 V
c. Vp Ip = Vs Is
50 x 4 = 100 x Is
Is = 200 /100 = 2 A
51. Select and write down the correct statements regarding a step down transformer from those given below.
a) current is the same in primary and secondary.
b) Power is the same in primary and secondary.
c) as compared to the secondary coil current Primary coil current is less
d) Current in the secondary is less than the current in the primary.
Answer:
b) Power is the same in primary and secondary.
c) Primary current is less than secondary current
52. 
a) which instrument is shown above? What is its working principle?
b) When 100V AC is applied at A, the current was 2A. Calculate the Voltage and current received at B.
Answer:
a. transformer, mutual induction
b. Vs/Vp = Ns/Np Vs/100 = 5000/10000 Vs = 50 V
P= V I = 100 x 2 = 200 W , input power=output power
53. The figure shows copper coils of the same thickness and different turns arranged in four circuits. If all the bulbs are of the same power answer the following questions analysing each figure.
b) If a soft iron core of the same size is inserted in each of the coils, which among the circuits shows the most change in the intensity of light.
Answer:
a. circuit 4
Self-induction is more if the number of tuns id more. So back emf increases.
b. circuit4, if the iron core is inserted self-induction again increases
54. Identify the relationship between the terms in the first pair and fill up the second pair accordingly
Generator: armature
moving coil microphone: ..............
Answer: voice coil
55. The figure of a DC generator is given below.
b) Compare the energy change taking place in an electric motor and a DC generator.
c) Though the current produced in a DC generator is AC, DC is received in the output. How?
Answer:
a) Slip rings used in Ac generator and Split rings used in DC generator
b) Motor: Electrical energy changes to mechanical energy
DC generator: Mechanical energy changes to electrical energy
c) the direction of electric current changes in each half rotation. The brushes connected to external circuit always comes in contact with an armature which moves in the same direction. So the direction of external current does not change
56. identify the relation in the first pair and complete the second pair.
Generator: Mechanical energy is changed into electrical energy
Moving coil microphone ........................................................
Answer: sound energy changes to electrical energy
57. The current in the primary of a step-up transformer that has no energy loss is........
[More, Less, equal]
Answer: More
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