Ncert Exercises & Solutions

27. The distance of a galaxy is of the order of 10²⁵m. Calculate the order of magnitude of time taken by light to reach us from the galaxy.

Hint:

Speed = \frac{distance}{time}

Step 1: Find the order of the time.

Given, the distance of the galaxy

= 10^{25} m

Speed of light

= 3 \times 10^{8} m / s

Hence, the time taken by light to reach us from the galaxy is,

\begin{array}{l} t = \frac{Distance}{Speed} = \frac{10^{25}}{3 \times 10^{8}} \approx \frac{1}{3} \times 10^{17} \\ = \frac{10}{3} \times 10^{16} = 3 .33 \times 10^{16} s \end{array}