Question

What is the luminous intensity of the sun if it produces the same illuminance on the earth as produced by a bulb of 10000 cd at a distance of 0.3 m. The distance between the sun and the earth is $1.5\times {10}^{11}m$.

• A. $2.5\times {10}^{23}cd$
• B. $2.5\times {10}^{19}cd$
• C. $2.5\times {10}^{27}cd$
• D. $2.5\times {10}^{36}cd$

Answer 1

The correct option is C $2.5\times {10}^{27}cd$

As $I_1=I_2$, hence
$\frac{L_1}{r_1^2}=\frac{L_2}{r_2^2}$
$\therefore$ Luminous intensity of sun
$L_2=\frac{L_1{r}_2^2}{r_1^2}=\frac{10000\times {(1.5\times {10}^{11})}^2}{{\left(0.3\right)}^2}$
$=2.5\times {10}^{27}cd$