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Physics · 2025 · 3 marks
CBSE 2025 · Region 4 · Set 1 · Q24
Two coils ' 1 ' and ' 2 ' are placed close to each other as shown in the figure. Find the direction of induced current in coil ' 1 ' in each of the…
Two coils ' $\displaystyle 1$ ' and ' $\displaystyle 2$ ' are placed close to each other as shown in the figure. Find the direction of induced current in coil ' $\displaystyle 1$ ' in each of the following situations, justifying your answers :
(a)
Coil ' $\displaystyle 2$ ' is moving towards coil ' $\displaystyle 1$ '.
(b)
Coil ' $\displaystyle 2$ ' is moving away from coil ' $\displaystyle 1$ '.
(c)
The resistance connected with coil ' $\displaystyle 2$ ' is increased keeping both the coils stationary.
Marking-scheme solution
(a)
Induced current will be clockwise.
Due to the direction of flow of current in coil $\displaystyle 2$, the face approaching coil $\displaystyle 1$ behaves like a south pole. Induced polarity on coil $\displaystyle 1$ viewed from the side of coil $\displaystyle 2$ will be south pole.
(b)
Induced current will be anticlockwise.
Due to direction of flow of current in coil $\displaystyle 2$, the face going away from coil $\displaystyle 1$ behaves like a south pole. Induced polarity on coil $\displaystyle 1$ viewed from the side of coil $\displaystyle 2$ will be north pole.
(c)
Induced current will be anticlockwise.
While the resistance in coil $\displaystyle 2$ is increasing, the magnetic flux associated with coil $\displaystyle 1$ is decreasing. Hence according to Lenz's law current will be induced in coil $\displaystyle 1$ momentarily, and after that no induced current in coil 1.
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CBSE Class 12 Physics past-paper question from the 2025 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.