Answer:
a) 2,042.1 years. b) 500 sec. c) 2.56 sec.
Explanation:
Visible light, is just an electromagnetic wave approximately within 400-700 nm) , so , in vacuum, propagates at a constant speed of 3. 10⁸ m/s.
So, in order to get the time needed for the light coming from any point of the universe can reach us, we just need to apply the velocity definition equation, as follows:
v = Δx / Δt, and solve for Δt, taking into account units.
a) if d = 6.44. 3.10¹⁸ m, and v = 3.10⁸ m/s, we find t as follows:
t = 6.44.3. 10¹⁸ / 3. 10⁸ s = 6.44 . 10¹⁰ sec.
Converting seconds to years:
6.44. 10¹⁰ sec . (1min/60 sec).(1h/60 min). (1d/24h)(1y/365d) = 2,042.1 years.
b) As the average distance earth-sun is 1.5.10⁸ m, we find t as follows:
t = 1.5 10¹¹ m / 3.10⁸ m/s = 500 sec = 8.33 min
c) As the average distance Earth-Moon is 3.84. 10⁸ m, we find t to be as follows:
t = 2. (3.84. 10⁸ m / 3. 10⁸ m/s) = 2.56 sec.
