Question

A generator converts mechanical energy to electrical energy. When a coil placed between two magnets rotates, the magnetic lines of force are disturbed. This induces a current in the coil. The image below shows a generator.



What could be done to make the lamp less bright?
A.
use a lamp that lights up with a lower current
B.
turn the coil faster
C.
move the magnets farther from the coil
D.
increase the strength of the magnets

Answer 1

Answer: C.

Reason: The induced emf (and thus current) depends on the magnetic flux through the coil and how quickly that flux changes (Faraday's law). Moving the magnets farther away reduces the magnetic flux and so lowers the induced emf/current — the lamp will be dimmer.

Notes on the other choices: turning the coil faster or using stronger magnets increases the emf and would make the lamp brighter. Using a lamp that "lights up with a lower current" would not make it dimmer (it would usually make it light at a lower current, i.e. relatively brighter for a given current).