Question

The magnetic field in the interstellar space of our galaxy has a magnitude of about 1.13 × 10-10 T. How much energy is stored in this field in a cube 12.7 light?years on edge? (For scale, note that the nearest star is 4.3 light?years distant and the radius of the galaxy is about 8 × 104 light?years.)

Answer 1

The energy per unit volume in the magnetic field is

The energy contained in the cube of volume V is

the side of cube a = 12.7 ly = 12.7 X 3 X 10⁸ X 365 X 24 X 60 X 60

a = 12.7 X 9.46 X 10¹⁵ m

a = 1.2 X 10¹⁷ m