Question

the energy associated with electric field Ue and with magnetic field Ub for an electromagnetic wave in free space
1. Ue greater than Ub
2.Ue=Ub
3.Ub greater than Ue
4.Ue =Ub/2

Answer 1

Ue is greater than Ub as electic field stores more energy then magnetic field

Answer 2

The electromagnetic field will be uE = uB

Energy associated with electric field = Ue (Given)

Energy associated with magnetic field = Ub (Given)

The energy density of magnetic field will be -

uB = B²0/2μ0, where B0 is the maximum value of a magnetic field.

Average energy density -

uE = ε0∈²/2

Thus, ∈0 =CB0, and C² = 1/μ0∈0

uE = ∈0/2 × C²B²

= ∈0/2 × 1/μ0∈0 × B²

= B²0/2μ0 = uB

uE = uB

Since, the energy density of electric and magnetic field is same, thus energy associated with the equal volume will be equal.

Hence, uE = uB