Question

A natural metallic ring is placed in a circular symmetrical uniform magnetic filed with its plane perpendicular to the filed. If the magnitude of field starts increasing with time, then

• A. the ring starts translating
• B. the ring starts rotating about its axis
• C. the ring slightly contracts
• D. the ring starts rotating about a diameter

Answer 1

The correct option is C the ring slightly contracts

field starts increasing with time

so $\frac{dB}{dt}$ will be +ve

so flux will increasing with time

so first of all the induced current

will oppose the change i.e increment

influx so it will get contract

to reduce area so that flux can

be decreased

mathematically $=\frac{-d\varphi }{dt}=\frac{-d}{dt}BA$

$\Rightarrow$ current $=\frac{e}{R}=\frac{-1}{R}\frac{d}{dt}\left(BA\right)$

Now fores $\overrightarrow{F}=i\overrightarrow{l}\times \overrightarrow{B}$ that will also be

perpendicular to circumference and toward center

so conttracting in nature