Question

Assume that the pictured magnet is being moved into the solenoid. If the polarity of the magnet is reversed and then moved into the solenoid, what happens? *

Answer 1

Answer:

The direction of induced emf is revered and hence the direction of the induced current.

Explanation:

If the polarity of the magnet is reversed, the direction if the field lines through the solenoid is also reversed, which according to Faraday's law means

$\varepsilon =N\dfrac{d\Phi}{dt} \rightarrow -N\dfrac{d\Phi}{dt}$

in other words, the direction of the magnetic flux is revered, and therefore, the direction of the induced emf is also revered.

Furthermore, according to Ohm's law

$I = \dfrac{\varepsilon}{R}$

which tells us that if the induced emf changes sign (is reversed)

$I = -\dfrac{\varepsilon}{R}$

the direction of the induced current is also reversed.