Question

Calculate the magnetic energy when the magnetic flux density is given by 32 units(in 10^8 order)

(a) 4.07

(b) 7.4

(c) 0.47

(d) 7.04

The question was asked during an interview.

This interesting question is from Magnostatic Energy in portion Magnetostics of Electromagnetic Theory

Answer 1

Correct answer is (a) 4.07

To explain I would say: The magnetic energy is given by E = 0.5 μ H^2 and we know that μH = B. On substituting we get a formula E = 0.5 B^2/μ. Put B = 32 and in air μ = 4π x 10^-7, we get E = 0.5 x 32^2/4π x 10^-7 = 4.07 x 10^8 units.