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shortcake1970
how long does it take light to reach us from the sun, 1.49 X 10 to the 8th km away
a red light has a wavelenght of 620nm. what is the frequency?
you can use v=s/t for the first and \(v=f \lambda\) for the second.
note: light has a speed of \(3 \times 10^8m/s\)
\[v=\frac dt\quad \implies\quad t=\frac dv\] \[d=1.49\times10^8 [\text {km}]=1.49\times10^{11}[\text m]\]\[v=c=3\times10^8 [\text{m/s}]\]