Q. What will be the colour of grass in blue light?
A. Grass will appear dark in colour in blue light, because it has the property of absorbing all other colours except its own colour. The blue rays falling on grass are absorbed by it and, therefore, it appears dark in colour.
Q. The colour of the same cloth when seen in electric light appears different from the colour when seen in daylight. Why ?
A. When a body is viewed in daylight, it reflects some colour which is called its natural colour. Electric light, on the other hand, is not pure. It may be deficient in some colours or has got some particular colour in excess. This is the reason why objects sometimes appear to be of a different colour in artificial light from their natural colour which they give in the white light.
Q. Why, when a gun is fired within a visible distance, the sound is heard a little after the smoke is seen ?
A. The velocity of light is much greater than that of sound. In other words, light travels faster than sound. Therefore, the flash of lightning or smoke of the gun is seen before the thunder of lightning or the sound of the gun being fired.