Question

A lamp placed 60 cm from a screen produces the same illumination as a standard 100 W lamp placed 90 cm away on the other side of the screen. The luminous intensity of the first lamp is

• A. $49.44W$
• B. $44.44W$
• C. $54.44W$
• D. $34.44W$

Answer 1

The correct option is B $44.44W$

For same illumination $\frac{Power}{r^2}$ will be same

=> $\frac{100}{{0.9}^2}=\frac{P}{{0.6}^2}$

=> P = $44.44W$