An optical lever is an extremely sensitive apparatus used to detect very small rotations. A lamp directs a narrow beam of light onto a small plane mirror fixed to a shaft whose rotation is being measured. The way the device works is illustrated in plan view. Light from the lamp is reflected by the mirror, producing a tiny bright spot on a scale positioned just above the lamp. The shaft and mirror turn through $1^\circ$. The light spot shifts along the scale. The table gives the angle $\theta$ through which the reflected beam turns, together with the conditions needed for high sensitivity. Which row is correct?
- A$\theta = 1^\circ$, the lamp and scale need to be as close to the mirror as possible
- B$\theta = 1^\circ$, the lamp and scale need to be as far from the mirror as possible
- C$\theta = 2^\circ$, the lamp and scale need to be as close to the mirror as possible
- D$\theta = 2^\circ$, the lamp and scale need to be as far from the mirror as possible