Question

The light from an electric bulb is normally incident on a small surface. If the surface is tilted by ${60}^0$ from this position, then the illuminace of the surface will become

• A. half
• B. one fourth
• C. double
• D. four times

Answer 1

The correct option is A half

Illuminance is proportional to Cos of angle at which light strikes the surface

If surface is tilted by ${60}^{\circ }$, then illuminace become Cos ${60}^{\circ }$ of original value

Cos ${60}^{\circ }$ = 0.5, so Illuminace becomes half

Answer. A) half