Question

A room is illuminated by an extended source. The illuminance at a particular portion of a wall can be increased by

• A. Moving the source
• B. rotating the source
• C. bringing some mirrors in proper positions
• D. changing the colour of the source

Answer 1

Answer: (A), (B), (C), (D)

The correct options are
A Moving the source
B rotating the source
C bringing some mirrors in proper positions
D changing the colour of the source

Moving the sources changes the intensity of light in particular direction by Doppler effect.

Rotating causes movement of sources, again giving rise to Doppler effect

Placing mirrors appropriately can cause the light rays to collect at a single point, increasing the intensity there.

Colour depends on the frequency of light, thus changing colour would change the energy per unit time emitted.