Question

A small circular flexible loop of wire of radius. $ r $ carries a current $ I. $ It is placed in a uniform magnetic field $B$. The tension in the loop will be doubled if

• A. I is halved
• B. B is halved
• C. r is doubled
• D. both B and I are doubled

Answer 1

Answer: (D)

When a circular flexible loop is placed in a magnetic field, a deflecting torque $(\tau)$ acts on it, this is given by
$ \tau =M B \sin \theta $
Also, $=I A $
$\therefore \tau =I A B \sin \theta=I \pi r^{2} B \sin \theta$
When $B$ and $I$ are doubled, the torque is doubled, hence tension is doubled.