Question

What is the order of magnitude of one light year?

• A. ${10}^{15}m$
• B. ${10}^{10}m$
• C. $9.2\times {10}^{15}m$
• D. ${10}^{16}m$

Answer 1

The correct option is D ${10}^{16}m$

One light year is the distance of light at a speed $3\times {10}^{8}m/s$ in 1 year.
Thus, $1$ light year $=3\times {10}^{8}m/s\times 1$ year $=3\times {10}^{8}m/s\times (365\times 24\times 3600s)=9.5\times {10}^{15}m$
According to rule of order of magnitude, as $9.5>5$ so 9.5 will be taken as 10.
Thus, order of magnitude of one light year $=10\times {10}^{15}={10}^{16}m$