Question
The distance of a galaxy is of the order of $10^{25}m$. Calculate the order of magnitude of time taken by light to reach us from the galaxy.
✓
Answer
According to the problem, distance of the galaxy = $10^{25}m$. Speed of light = $3 \times 10^8m/s$ Hence, time taken by light to reach us from galaxy is, $\text{t}=\frac{\text{Distance}}{\text{Speed}}=\frac{10^{25}\text{m}}{3\times10^8\text{m/s}}=\frac{1}{3}\times10^{17}$ $=\frac{10}{3}\times10^{16}=3.33\times10^{16}\text{s}$
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