Question

The focal length of mirror used in Head-
light of car is 20 cm. At what distance,
bulb is arranged then parallel beam is
emitted.
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1) 20 cm 2) 10 cm 3) 5 cm 4) 2 cm
Anbient​

Answer 1

Answer:

If the mirror is used as head light of a car, then it is a concave mirror

We know that light rays passing through the focus of a concave mirror emerge parallel to the principle axis after reflection.

So, in order to get a parallel beam, the bulb should be placed at the focus of the mirror, ie, at 20cm from the pole of the mirror.

Thus, answer is 1) 20cm