Question

Which device works on the principle of mutual induction?

• A. Tube light
• B. Transformer
• C. Photodiode
• D. LED

Hint:

Look for the device that has two separate coils sharing a common changing magnetic flux.

Answer 1

The Correct Option is B

Step 1: Mutual induction happens when a changing current in one coil produces a changing magnetic flux that links with a nearby second coil, inducing an emf in that second coil.

Step 2: A transformer has exactly this setup, a primary coil and a secondary coil wound on a common iron core. When alternating current flows in the primary, the changing flux passes through the core into the secondary coil and induces an emf there. This is used to step voltage up or down.

Step 3: The formula that describes this is \(\varepsilon = -M \dfrac{dI}{dt}\), where M is the mutual inductance between the two coils.

Step 4: Now the wrong options. A tube light uses a choke coil which works through self induction, opposing sudden changes of current in the same coil, not through two separate coils sharing flux. A photodiode works through the photoelectric effect, light striking a semiconductor junction and freeing charge carriers. An LED works through electroluminescence, electrons and holes recombining in a semiconductor to emit light. Neither of these involves two coils linked by magnetic flux.

Step 5: So the correct answer is the transformer.