Question

A particular star is d = 40.1 light-years (ly) away, with a power output of P = 4.50 ✕ 1026 W. Note that one light-year is the distance traveled by the light through a vacuum in one year.

(a) Calculate the intensity of the emitted light at distance d (in nW/m2). nW/m2

(b) What is the power of the emitted light intercepted by the Earth (in kW)? (The radius of Earth is 6.37 ✕ 106 m.) kW What If?

Of the more than 150 stars within 20 light-years of Earth, 90 are very dim red dwarf stars each with an average luminosity of 2.00 ✕ 1025 W, about 5% the luminosity of the Sun. If the average distance of these objects from the Earth is 10.0 ly, find the following.

(c) the ratio of the total intensity of starlight from these 90 stars to the intensity of the single bright star found in part (a) Idwarf stars Isingle star =

(d) the ratio of the total power the Earth intercepts from these stars to the power intercepted from the bright star in part (b) Pdwarf stars Psingle star =

Answer 1