Question

A system consists of two coils $\text{A}$ & $\text{B}$. The coil $\text{A}$ carries a steady current $I$ while the coil $\text{B}$ is suspended nearby as shown. Now if the system is heated to raise the temperature of two coils steadily then

• A. The two coils show attraction.
• B. The two coils show repulsion.
• C. There is no change in the position of two coils.
• D. Induction of current is not possible in coil $B$.

Answer 1

The correct option is A The two coils show attraction.


Initially as the current is constant. So, flux through coil $\text{B}$ is also constant.

As the temperature of the coils is increased.

$\because R=R_0(1+\alpha \Delta T)\Rightarrow R\uparrow \uparrow$

$R\uparrow \uparrow \Rightarrow I\downarrow \downarrow$ $\left(\text{in loop}A\right)$

As, $I\downarrow \downarrow \Rightarrow flux,\varphi \downarrow \downarrow$

So, the current will be induced in coil $\text{B}$.

So, the direction of induced current in coil $\text{B}$ will be such that it will try to increase the flux $\varphi$.

Now, $B_{induced}$ will support $B_{exist}$ only when, the current in both loops is in same direction.

Therefore, the two loops will show attraction.

Hence, option $\left(A\right)$ is correct.