Optics Question 496
Question: Two stars situated at distances of 1 and 10 light years respectively from the earth appear to possess the same brightness. The ratio of their real brightness is
[NCERT 1981]
Options:
A) 1 : 10
B) 10 : 1
C) 1 : 100
D) 100 : 1
Show Answer
Answer:
Correct Answer: C
Solution:
$ I=\frac{L}{r^{2}} $
$ \Rightarrow \frac{L _{1}}{r _{1}^{2}}=\frac{L _{2}}{r _{2}^{2}} $ (I is same)
$ \Rightarrow \frac{L _{1}}{L _{2}}=\frac{r _{1}^{2}}{r _{2}^{2}}={{( \frac{1}{10} )}^{2}}=1:100 $ .
