5. Exercises

1. Light and Radiation

Electromagnetic Waves (2/4)

Question: Time lapse of sunlight and moonlight reaching the earth

The distance between the sun and the earth is approx. 150·106 km. How much time does it take (in seconds and in minutes) for the light emitted by the sun to reach the earth?

The distance between the moon and the earth is 384 000 km, hence much shorter. How much time does it take for the sunlight reflected by the moon surface to reach the earth?

Answer:

The time lapse of sunlight to reach the earth is

t= x c = 150⋅ 10 9 m 0.3⋅ 10 9 m/s =500 s

or 8.33 minutes. For the moonlight it is

t= x c = 0.384⋅ 10 9 m 0.3⋅ 10 9 m/s =1.28 s