What is the energy density in the magnetic field 25 cm from a long straight wire carrying a current of 12 a? (μ0 = 4π × 10-7 t · m/a) what is the energy density in the magnetic field 25 cm from a long straight wire carrying a current of 12 a? (μ0 = 4π × 10-7 t · m/a)?

Explanation:

First of all, we need to calculate the magnetic field magnitude at 25 cm from the wire, which is given by

where

μ0 = 4π × 10-7 t · m/a is the vacuum permeability

I = 12 A is the current in the wire

r = 25 cm = 0.25 m is the distance from the wire

Substituting,

Now we can calculate the energy density of the magnetic field, which is given by

And substituting, we find

small = small current large mag large current

the minimum amperage that the current in this wire would have to have so that its weight is completely supported by the magnetic force due to earth's field, assuming that no other forces except gravity act on it