Question

An aluminum ring $\text{B}$ faces an electromagnet $\text{A}$. The current through $\text{A}$ can be altered. Then which of the following statements is correct:

• A. If current decreases, $\text{A}$ will repel $\text{B}$
• B. Whether current increases or decreases, $\text{B}$ will not experience any force
• C. If current increases, $\text{A}$ will repel $\text{B}$
• D. If current increases, $\text{A}$ wil attract $\text{B}$

Answer 1

The correct option is C If current increases, $\text{A}$ will repel $\text{B}$

If the current increases, the flux linked with the two will increase.

Therefore, according to Lenz law, a current will be induced such that it opposes the increase in flux.

This results in an induced magnetic field that repels original magnetic field of $\text{A}$ and hence $\text{A}$ and $\text{B}$ repel.

however, if the current decreases, the flux between the two will decrease.

Therefore, by Lenz law, a current will be induced such that it opposes the decrease in flux . This results in an induced magnetic field that is in the same direction as the original magnetic field of $\text{A}$ and hence $\text{A}$ and $\text{B}$ attract.

Hence, option ($C$) is the correct answer.