A circular lawn of diameter 20 meters on a horizontal plane is to be illuminated by a light-source placed vertically above the centre of the lawn. It is known that the illuminance at a point $P$ on the lawn is given by the formula $I = \frac{C \sin\theta}{d^2}$ for some constant $C$, where $d$ is the distance of $P$ from the light-source and $\theta$ is the angle between the line joining the centre of the lawn to $P$ and the line joining the light-source to $P$. Then the maximum possible illuminance at a point on the circumference of the lawn is (A) $\frac{C}{75\sqrt{3}}$ (B) $\frac{C}{100\sqrt{3}}$ (C) $\frac{C}{150\sqrt{3}}$ (D) $\frac{C}{250\sqrt{3}}$.
A circular lawn of diameter 20 meters on a horizontal plane is to be illuminated by a light-source placed vertically above the centre of the lawn. It is known that the illuminance at a point $P$ on the lawn is given by the formula $I = \frac{C \sin\theta}{d^2}$ for some constant $C$, where $d$ is the distance of $P$ from the light-source and $\theta$ is the angle between the line joining the centre of the lawn to $P$ and the line joining the light-source to $P$. Then the maximum possible illuminance at a point on the circumference of the lawn is\\
(A) $\frac{C}{75\sqrt{3}}$\\
(B) $\frac{C}{100\sqrt{3}}$\\
(C) $\frac{C}{150\sqrt{3}}$\\
(D) $\frac{C}{250\sqrt{3}}$.