A lamp is at a height of 4 m from a table. If the height is increased by 1 m , the illumination on t

Question

A lamp is at a height of 4 m from a table. If the height is increased by 1 m , the illumination on the table will decrease by\

Professor PC Thomas Classes · Answer

$\mathrm{I}=\frac{\mathrm{L}}{\mathrm{d}^{2}}$\ $I_{1}=\frac{L}{4^{2}}=\frac{L}{16}$\ $\mathrm{I}_{2}=\frac{\mathrm{L}}{5^{2}}=\frac{\mathrm{L}}{25}$\ $\mathrm{I}_{1}-\mathrm{I}_{2}=\frac{\mathrm{L}}{16}-\frac{\mathrm{L}}{25}=\frac{9 \mathrm{~L}}{16 	imes 25}$\ $\frac{\mathrm{I}_{\mathrm{I}}-\mathrm{I}_{2}}{\mathrm{I}_{1}}=\frac{9 \mathrm{~L}}{16 	imes 25} 	imes \frac{16}{\mathrm{~L}}=\frac{9}{25} 	imes 100=\%$\