Magnetics 3 Question 7
7. A rectangular loop carrying a current $i$ is situated near a long straight wire such that the wire is parallel to one of the sides of the loop and is in the plane of the loop. If steady current $I$ is established in the wire as shown in the figure, the loop will
$(1985,2 M)$ (a) rotate about an axis parallel to the wire
(b) move away from the wire
(c) move towards the wire
(d) remain stationary
Fill in the Blank
Show Answer
Answer:
Correct Answer: 7. (c)
Solution:
- Straight wire will produce a non-uniform field to the right of it. $\mathbf{F} _{b c}$ and $\mathbf{F} _{d a}$ will be calculated by integration but these two forces will cancel each other. Further force on wire $a b$ will be towards the long wire and on wire $c d$ will be away from the long wire. But since the wire $a b$ is nearer to the long wire, force of attraction towards the long wire will be more. Hence, the loop will move towards the wire.
