(a) How long in seconds does it take a radio signal to travel 210 km from a tran
ID: 1426054 • Letter: #
Question
(a) How long in seconds does it take a radio signal to travel 210 km from a transmitter to a receiving antenna? (b) We see a full Moon by reflected sunlight. How much earlier did the light that enters our eye leave the Sun? The Earth – Moon and Earth – Sun distances are 3.8x105 km and 1.5 × 108 km, respectively. (c) What is the round-trip travel time in seconds for light between Earth and a spaceship at a 8.3 × 106 km distance from Earth? (d) Suppose astronomers observe a supernova about 7900 light-years (ly) distant. How long ago in years did the explosion actually occur?
Explanation / Answer
(a)
given that
distance traveled by the signal
s= 210 km .
so
t = s/c (where c is velocity of light )
t = (210*10^3) /3*10^8
t = 0.0007 s
(b)
distance b/w sun & earth is
s = 1.5*10^8 km
t = s/c (where c is velocity of light )
t = (1.5*10^8*10^3)/3*10^8
t= 500 s
t= 8.33 min
(c)
distance b/w earth & spaceship is
s = 8.3*10^6 km = 8.3*10^9 m
t = s/c (where c is velocity of light )
t = (8.3*10^9 ) /(3*10^8)
t = 27.66 s
(d)
Let explosion recorded at present time which is 2016 A.D.
so
= 2016 - 7900
=5884 BCE
the explosion actually occurs 5884 BCE ago .
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