The luminous flux of a 40 watt bulb is 400 lumen. What is luminous efficiency of the bulb?

What are luminous bodies ?

What are non-luminous bodies?

Calculate the electric field and magnetic field produced by the rediation coming from a 100 W bulb at a distance of 3 m. Assume that the efficiency of the bulb is 2.5 % and it is a point source.

Calculate the resistance of a bulb rated 100 W, 220V. What is the current flowing in the bulb when connected across a potential difference of 220 V?

The image of a small electric bulb fixed on the wall of a room is to be obtained on the opposite wall 3m away by means of a large convex lens. What is the maximum possible focal length of the lens required for the purpose?

(i) A lot of 20 bulbs contain 4 defective ones. One bulb is drawn at random from the lot. What is the probability that this bulb is defective? (ii) Suppose the bulb drawn in (i) is not defective and is not replaced. Now one bulb is drawn at random from the rest. Whal is the probability that this bulb is not defective ?