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Question

(B) The intensity of illumination $I$ on a surface is given by the formula: $I = \frac{L \cos 	heta}{r^2}$,where $L$ is the luminous intensity of the

Vedclass · Accepted Answer

$40$

Vedclass · Answer

(B) The intensity of illumination $I$ on a surface is given by the formula: $I = \frac{L \cos 	heta}{r^2}$,where $L$ is the luminous intensity of the source in candela,$r$ is the distance,and $	heta$ is the angle with the normal.Given:$I = 5 	imes 10^{-4} \ phot = 5 	imes 10^{-4} \ lumen/cm^2 = 5 	imes 10^{-4} 	imes 10^4 \ lumen/m^2 = 5 \ lumen/m^2$.$r = 2 \ m$.$	heta = 60^{\circ}$.Rearranging the formula to find $L$:$L = \frac{I 	imes r^2}{\cos 	heta}$.Substituting the values:$L = \frac{5 	imes 2^2}{\cos 60^{\circ}} = \frac{5 	imes 4}{0.5} = \frac{20}{0.5} = 40 \ candela$.Thus,the correct option is $B$.

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