Solved Examples

1. A magnetic field of 2.5 T passes perpendicular to a disc of radius 2 cm. Find the magnetic flux associated with the disc.

Solution: B = 2.5 T, r = 2 cm = 2 × 10–2 m, θ = 0,

ΦB=?ΦB=BAcosθ=2.5×π(2×10−2)2×cos0=3.14×10−3WbΦ�=?Φ�=������=2.5×�(2×10−2)2×���0=3.14×10−3��

2. A coil of area of cross section 10–2 m² and 100 turns is placed in a magnetic field of strength 1 T, with its axis making an angle 60° with the field. Find the total flux associated with the field.

Solution: B = 1 T, A = 10–2 m²,

θ=60∘,n=100,ΦB=?ΦB=nBAcosθ=100×1×10(−2)×cos60∘=0.5Wb�=60∘,�=100,Φ�=?Φ�=�������=100×1×10(−2)×���60∘=0.5��

3. When the coil is rotated between the pole pieces of a magnet as shown, during one complete rotation of the coil, how often will the magnetic flux linked with the coil be maximum and minimum?

Options:

(a) maximum and minimum once each

(b) maximum and minimum twice each

(c) maximum once, minimum twice

(d) maximum twice, minimum once

Answer: (b)