Question

A wire 88 cm long bent into a circular loop is placed perpendicular to the magnetic field of flux density 2.5 Wb. Within 0.5 s, the loop is changed into a square and flux density is increased to 3.0 Wb. The value of e.m.f. induced is :

• A. 0.018V
• B. 0.016V
• C. 0.020V
• D. 0.012V

Answer 1

The correct option is A 0.018V

Answer is A.
The magnetic flux $\varphi =B\times A$ depends on the magnetic field, the area
of the loop, and their relative orientation.
In this case, the wire 88 cm long bent into a circular loop is placed perpendicular to the magnetic field and Within 0.5 s, the loop is changed into a square.
Magnetic Flux when in a circular loop:
Circumference of the loop = $2\times 3.14\times r=88cm$.
So, the radius of the loop r = 14 cm.

Magnetic field $\varphi =B\times A=2.5\times 3.14\times 0.14\times 0.14=0.154Wb$.

Magnetic Flux when in a square:
Circumference of the square = $4r=88cm$

So, length of the side of the square is $\frac{88}{4}=22cm$.

Magnetic feild ${\varphi }^{\prime }=B\times A=3\times 0.22\times 0.22=0.1452Wb$.

The total induced emf is $\frac{0.154-0.1452}{0.5}=0.018V$.

Therefore, the value of e.m.f induced is 0.018 V.