Question

Two stars in the sky give off the same amount of total energy, but Star A appears 121 times fainter in our night sky than Star B. How many times farther away is Star A than Star B?

Answer 1

According to EM theory

I = U c

I = intensity of the light

U=energy density of the light =

c= velocity of the light

V=volume of emission (for spherical source )

r=distance travel by the light

E=energy of the light

therefore

for the same cross-area of measurement

1-for star A

2-for star B

now I₁ = 121 I₂

and E₁ = E₂

so

therefor distance of the starB is 11 times distance of the starA