Question

A conducting wire frame is placed in a magnetic field which is directed into the plane of the paper (figure). The magnetic field is increasing at constant rate. The directions of induced currents in wires $AB$ and $CD$ are

• A. $B$ to $A$ and $D$ to $C$
• B. $A$ to $B$ and $C$ to $D$
• C. $A$ to $B$ and $D$ to $C$
• D. $B$ to $A$ and $C$ to $D$
• E. answer required

Answer 1

The correct option is A $B$ to $A$ and $D$ to $C$

Consider the surface facing upwards having points A, B, C and D in anticlockwise direction when viewing towards the surface from above. Let this be $\overrightarrow{S}$
flux = $\overrightarrow{S}\times \overrightarrow{B}$
As the flux increases, by Lenz's Law the induced current will be in the direction C B A D C, so as to oppose the increase in flux.