Question

As shown in the figure a magnet is moved with a fast speed towards a coil at rest. Due to this induced emf, induced current and induced charge in the coil is $E,I$ and $Q$ respectively. If the speed of the magnet is doubled, the incorrect statement is

• A. E increases
• B. I increases
• C. Q remains same
• D. Q decreases

Answer 1

Answer: (D)

Induced emf $E=IR$
or$I=\frac{E}{R}$
and$E=\frac{d\varphi }{dt}$
$\therefore I=\frac{d\varphi }{dtR}$
Induced charge $q=I.dt$
$=\frac{d\varphi }{R}$
If speed is doubled, then dt decrease, hence, $E,I$ increases, but $q$ will not increase.