A plane mirror of circular shape with radius r = 20 cm is fixed to the celling. A bulb is to be placed on the axis of the mirror. A circular area of the radius R = 1m on the floor is to be illuminated after reflection of light from the mirror. The height of the room is 3m . What is the maximum distance from the centre of the mirror and the bulb so that the required area is illuminated ?

Answer

75 cm

Explanation

`DeltaABC ` & `DeltaAB'C`
`(x)/(0.20) = (x+3)/(1)`
x = 0.2x + 0.6`
`0.8x = 0.6 implies x = (3)/(4)` cm
x = 75 cm