Question

What is the order of magnitude of the distance of a quasar from us if light takes 2.9 billion years to reach us ?

• A. $2.7\times {10}^{25}m$
• B. ${10}^{25}m$
• C. ${10}^{2}4m$
• D. $3\times {10}^{25}m$

Answer 1

Answer: (B)

${10}^{25}m$

Here, time taken $t=2.9$ billion years $=2.9\times {10}^9$ years $=2.9\times {10}^9\times (365\times 24\times 3600)s=9.14\times {10}^{16}s$
Distance $=$ velocity $\times$ time
or $d=(3\times {10}^8)\times (9.14\times {10}^{16})=2.74\times {10}^{25}m$
As $2.74<5$ so it will be taken as 1.
Thus, the order of magnitude of distance $d=1\times {10}^{25}m={10}^{25}m$