iGCSE Physics (0625) 4.5.1 Electromagnetic induction-Exam Style Questions- New Syllabus
▶️ Answer/Explanation
Detailed solution:
The magnitude of the induced e.m.f. is determined by the rate at which magnetic field lines are cut by the conductor.
Increasing the speed of the magnet increases this rate, directly resulting in a higher induced voltage.
A stronger magnet provides a greater magnetic flux density, meaning more field lines are cut per second during motion.
Increasing the number of turns (N) on the coil increases the total flux linkage, as e.m.f.∝N.
Since all three proposed changes independently increase the rate of change of magnetic flux linkage, they all increase the e.m.f.
Therefore, the correct choice is 1, 2, and 3, making option A the correct answer.
▶️ Answer/Explanation
Detailed solution:
Electromagnetic induction occurs when a conductor “cuts” through magnetic field lines, causing a change in the magnetic flux linkage.
According to Faraday’s Law, the induced e.m.f. ($\varepsilon$) is proportional to the rate of change of magnetic flux ($\Phi$), expressed as $\varepsilon = -N\frac{\Delta\Phi}{\Delta t}$.
Simply connecting the wire to a power supply (Option A) or earth (Option B) creates a circuit or discharge but does not “induce” an e.m.f. from the field.
Heating the wire (Option C) changes its resistance but does not affect the magnetic flux linkage.
Moving the wire (Option D) through the uniform magnetic field ensures the conductor cuts the field lines, directly triggering induction.
Therefore, physical motion of the conductor relative to the magnetic field is the necessary condition for an induced e.m.f. in this context.
Question
Which action will not magnetise a rod?
placing a copper rod inside a coil carrying a direct current
stroking a steel rod with a permanent magnet
hammering a steel rod aligned with the Earth’s magnetic field
placing a soft-iron rod close to a permanent magnet
Answer/Explanation
Ans: A