Electromagnetic Induction
Class 10th Physics Part I Kerala Board Solution
- (a) Write down the name of parts numbered in the diagram. (b) State the working principle…
- (a) Write down the name of parts numbered in the diagram. (b) State the working principle…
- Copper wires of the same length and thickness are connected to points A and B in all the…
- What type of a transformer is this? The current in the secondary coil of a transformer is…
- If 200 V is available in the secondary coil of this transformer, what is the voltage in…
- Explain the working principle of a transformer. The current in the secondary coil of a…
- In connection with the working of a microphone, a few statements are given in boxes.…
- Given below is a graph of the output from the secondary coil of a transformer. Observe the…
- Thick insulated copper wires are used in the primary coil of a step up transformer and in…
- Make coils of a different number of turns using insulated copper wire. Use magnets of…
- Michael Faraday, the father of electricity, did not even get elementary education. Are you…
- Energy is invaluable, especially electrical energy. Society must be convinced of the…
- Collect information regarding microphones which work under different physical principles.…
- Compare the induced current obtained when the armature coil rotates once in between the…
Let Us Assess
Question 1.
(a) Write down the name of parts numbered in the diagram.
(b) State the working principle of this device.
Answer:
(a) 1) Magnetic north pole of field magnet.
2)Armature
3)Slip Rings
(b) It converts mechanical energy to electrical energy, and operates on the principle of electromagnetic induction, i.e. changing magnetic field induces an electric field.
Question 2.
(a) Write down the name of parts numbered in the diagram.
(b) State the working principle of this device.
Answer:
(a) 1) Magnetic north pole of field magnet.
2)Armature
3)Slip Rings
(b) It converts mechanical energy to electrical energy, and operates on the principle of electromagnetic induction, i.e. changing magnetic field induces an electric field.
Question 3.
Copper wires of the same length and thickness are connected to points A and B in all the three circuits. In circuit (a) copper wire is not coiled. In circuits (b) and (c), the copper wire is coiled. Observe the circuits and answer the following questions.
(a) When circuit (a) is switched on, what do you observe?
(b) When circuit (b) is switched on, what change do you observe in the intensity of light? Justify your answer.
(c) When circuit (c) is switched on, what change do you observe in the intensity of light? Justify your answer.
Answer:
(a)The bulb in (a) glows brightly.
(b) The bulb in (b) glows brightly. There is no change in intensity as the power supply is DC. So, inductance has no role to play.
(c) The intensity of light reduces. The coiled wire behaves as an inductor and a back emf is generated. This reduces the effective voltage of the circuit.
Question 4.
The current in the secondary coil of a transformer is 1A and that in the primary is 0.5 A.
What type of a transformer is this?
Answer:
The equation used to work out the power for the primary coil and the secondary coil of a transformer is:
P = V × I
where:
P is the power in watts, W
V is the potential difference in volts, V
I is the current in amperes (amps), A
Because the current is larger in the secondary coil of the transformer is larger as compared to that in primary coil.
This means the voltage in the secondary coil must be smaller in order to maintain constant power. Hence, the transformer which results in low voltage is called a step-down transformer.
Question 5.
The current in the secondary coil of a transformer is 1A and that in the primary is 0.5 A.
If 200 V is available in the secondary coil of this transformer, what is the voltage in the primary?
Answer:
Transformer ratio = 
Now,
⇒ Voltage is primary coil, V = 400 V.
Question 6.
The current in the secondary coil of a transformer is 1A and that in the primary is 0.5 A.
Explain the working principle of a transformer.
Answer:
The diagram is shown below:
i. In a transformer, the AC voltage applied to the primary coil produces a varying magnetic field.
ii. By electromagnetic induction, an emf is induced in the primary. The change of flux in the primary coil is linked with the secondary.
iii. Hence an emf is induced in the secondary coil as well.
iv. Thus the emf induced in each turn of the primary coil and secondary coil will be same.
v. In this way, the voltage across the primary coil is stepped up or stepped down depending on the turns ratio of the primary and secondary coils.
Question 7.
In connection with the working of a microphone, a few statements are given in boxes.
Arrange them in the proper order.
Answer:
Question 8.
Given below is a graph of the output from the secondary coil of a transformer. Observe the graph and answer the following questions.
(a) The electricity produced from which type of generator does the given graph represent?
(b) The maximum and minimum voltages in A, B, C are the same Give the reason.
Answer:
(a) Electricity has been produced by a three-phase generator.
(b) The maximum and minimum voltages in A, B, C are the same because there are 3 identical windings that are placed 120 electrical degrees apart from each other. The loads are balanced.
Question 9.
Thick insulated copper wires are used in the primary coil of a step up transformer and in the secondary of a step-down transformer. What is the necessity of doing this? Why is it so?
Answer:
The thicker the wire, the greater is its cross-section(A), the lesser is its resistance(because of 
). So, the power dissipated is reduced. This is important because one of the main purposes of a transformer is power transfer at required voltages.
Extended Activities
Question 1.Make coils of a different number of turns using insulated copper wire. Use magnets of different strengths to produce induced emf. Present this activity in the science club.
Answer:
The greater the number of coils and greater the strength of the magnets used, greater will be the magnitude of induced emf.
Question 2.
Michael Faraday, the father of electricity, did not even get elementary education. Are you not inspired by the achievements of Faraday in the field of science?
Conduct a seminar on “Contributions of Faraday and the hard work behind it.”
Answer:
Talk about the early life of Michael Faraday, how he worked as a bookbinder’s apprentice and how he read and learned so much. Then proceed to his encounter with Humphrey Davy and how he was influenced by his lectures, Faraday’s beginning in the world of physics as Davy’s apprentice. Finally describe his Christmas lectures for the free public, and how he revolutionized the world of science with his limited resources.
Question 3.
Energy is invaluable, especially electrical energy. Society must be convinced of the necessity of reducing the consumption of electrical energy. Prepare and propagate posters for this purpose.
Answer:
Question 4.
Collect information regarding microphones which work under different physical principles.
Answer:
Several different types of microphone are in use, which employ different methods to convert the air pressure variations of a sound wave to an electrical signal. The most common are the dynamic microphone, which uses a coil of wire suspended in a magnetic field; the condenser microphone, which uses the vibrating diaphragm as a capacitor plate, and the piezoelectric microphone, which uses a crystal of piezoelectric material. Some even operate on the principles of fiber optics.
Question 5.
Compare the induced current obtained when the armature coil rotates once in between the poles of a magnet, and the induced current obtained when the experiment using a magnet and coil was performed.
Answer:
If the magnet strength and the no. of coils are equivalent in both cases, then the induced currents will be equal. This is because electromagnetic induction occurs due to relative motion between the magnet and the coil.