Question

The distance of gravity is of the order of 10rais to 25m.calculate the order of magnitude of time taken by light to reach us from the galaxy

Answer 1

$$\begin{gathered} \mathrm{Speed}\mathrm{of}\mathrm{light}=3\times {10}^8\mathrm{m}/\mathrm{s} \\ \mathrm{and}\mathrm{distance}\mathrm{of}\mathrm{galaxy}={10}^{25}\mathrm{m} \\ \mathrm{So}\mathrm{time}\mathrm{taken}=\frac{\mathrm{distance}}{\mathrm{speed}}=\frac{{10}^{25}}{3\times {10}^8}=\frac{1}{3}\times {10}^{25-8} \\ =\frac{1}{3}\times {10}^{17} \\ \mathrm{Hence}\mathrm{the}\mathrm{time}\mathrm{taken}\mathrm{will}\mathrm{be}\mathrm{of}\mathrm{order}\mathrm{of}{10}^{17}. \end{gathered}$$