Question

Two lamps of powers ${{P}_{1}}$ and ${{P}_{2}}$ are placed on either side of a paper having an oil spot. The lamps are at distances of 1 m and 2 m respectively on either side of the paper and the oil spot is invisible. What is the value of ${{P}_{1}}/{{P}_{2}}$ ?

• A. 0.25
• B. 0.4
• C. 0.5
• D. 0.6

Answer 1

Answer: (A)

0.25

Answer 2

Here $\frac{{{P}_{1}}}{{{P}_{2}}}={{\left( \frac{{{r}_{1}}}{{{r}_{2}}} \right)}^{2}}$
$\frac{{{P}_{1}}}{{{P}_{2}}}={{\left( \frac{1}{2} \right)}^{2}}$
$\frac{{{P}_{1}}}{{{P}_{2}}}=0.25$