Electromagnetic Induction (Faraday) - UNSOLVED PRACTICE SET

Q7. What is electromagnetic induction? State the basic condition required for an EMF to be induced in a coil.

Q8. Describe a simple experiment to demonstrate electromagnetic induction using a bar magnet, a coil of wire, and a galvanometer.

Q9. A bar magnet is pushed into a coil and the galvanometer shows a deflection. What happens to the deflection when:
(a) the magnet is held stationary inside the coil, and
(b) the magnet is pulled out of the coil?

Q10. How does the speed of relative motion between a magnet and a coil affect the magnitude of the induced EMF? Give one practical implication of this relationship.

Q11. State Lenz's Law. How does it relate to the conservation of energy?

Q12. Why is no current induced in a coil when a magnet is held stationary near it, even though the magnetic field is present and quite strong?

Q13. Describe Faraday's experiments on electromagnetic induction in detail. Your answer must cover:
(a) the setup — a coil connected to a galvanometer and a bar magnet,
(b) the observation when the magnet is moved toward the coil,
(c) the observation when the magnet is moved away,
(d) the observation when the magnet is held stationary,
(e) how the speed of the magnet's motion affects the induced current, and
(f) the overall conclusion about the relationship between changing magnetic fields and induced EMF/current.

Q14. Explain Lenz's Law and its connection to the conservation of energy.
(a) State Lenz's Law clearly.
(b) When a magnet's North pole approaches a coil, does the induced current create a North or South pole at the near end of the coil (to oppose the approaching magnet)? Explain your reasoning.
(c) When the magnet is pulled away, does the induced current now attract or repel the magnet?
(d) Why must the induced current always 'oppose' the change — what would happen (hypothetically) if it aided the change instead, in terms of energy?
(e) Connect this to why you feel resistance when pushing a magnet into a coil — where does the work you do go?

Q15. Compare electromagnetic induction (Faraday) with the magnetic effect of current (Oersted) as two complementary discoveries. 

(a) What did Oersted's experiment demonstrate (briefly recall)?
(b) What does Faraday's experiment demonstrate? 

(c) How are these two discoveries 'opposite but related' — explain in terms of cause and effect. 

(d) Together, these two discoveries form the basis of which two major electrical devices (one converts electrical to mechanical, the other mechanical to electrical)? 

(e) Why are both discoveries considered foundational to the entire modern electrical power industry, from the Bhakra Nangal hydroelectric dam to a hand-cranked emergency torch?

Q16. A student moves a bar magnet's North pole toward a coil connected to a galvanometer and observes a deflection of 10 divisions to the right.
(a) If the magnet is now moved toward the coil at twice the speed, predict (qualitatively, with reasoning) what the new deflection might be.
(b) If the magnet's North pole is now moved AWAY from the coil at the original speed, what happens to the direction of the galvanometer deflection compared to the first observation?
(c) If the magnet is replaced with one of double the strength (moved at the original speed toward the coil), how would the deflection compare to the first observation?

Q17. A coil of 100 turns is used in an electromagnetic induction experiment. When a magnet is moved through it, an EMF of 2 V is induced.
(a) If a similar coil with 200 turns (same dimensions, same magnet motion) is used instead, what EMF would you expect, given that induced EMF is proportional to the number of turns?
(b) If the original 100-turn coil is used but the magnet is moved through it twice as fast, what EMF would you expect?
(c) If both changes (200 turns AND twice the speed) are combined, what EMF would you expect?

Q18. A hand-cranked emergency torch (popular in rural India during power cuts) contains a small generator based on electromagnetic induction.
(a) Explain how turning the hand crank produces an electric current to light the LED.
(b) Why does the torch require continuous cranking to keep the LED lit, rather than producing a one-time charge?
(c) If you crank the handle faster, what happens to the brightness of the LED? Explain using the factors affecting induced EMF.
(d) Such torches often have a small battery/capacitor as well — what is its purpose, and how does it relate to the intermittent nature of hand-cranking?