Question

A rod with circular cross-section area $2\, cm ^2$ and length $40 cm$ is wound uniformly with $400$ turns of an insulated wire If a current of 0.4 A flows in the wire windings, the total magnetic flux produced inside windings is $4 \pi \times 10^{-6}\, Wb$ The relative permeability of the rod is(Given : Permeability of vacuum $\mu_0=4 \pi \times 10^{-7}\, NA ^{-2}$ )

• A. $125$
• B. $12.5$
• C. $\frac{5}{16}$
• D. $\frac{32}{5}$

Answer 1

Answer: (A)

$125$

Answer 2

ϕ = μr​μ0​$\frac nl$​I × A

ϕ = 4 π × 10−6 x 4 π × 10−7 $\frac {400}{0.40}$ x 0.4 x 2 x 10 -4
μr​=125

So, the correct answer is (A): 125