A point source of light is kept at a distance of 15 cm from a converging lens, on its optical axis. The focal length of the lens is 10 cm and its diameter is 3 cm . A screen is placed on the other side of the lens, perpendicular to the axis of the lens, at a distance 20 cm . from it. Then find the area of the illuminated part of the screen?

Question

A point source of light is kept at a distance of 15 cm from a converging lens, on its optical axis. The focal length of the lens is 10 cm and its diameter is 3 cm . A screen is placed on the other side of the lens, perpendicular to the axis of the lens, at a distance 20 cm . from it. Then find the area of the illuminated part of the screen?, π 4 cm 2, π 6 cm 2, π 2 cm 2, π 3 cm 2

MARKS App · Accepted Answer

1 V - 1 u = 1 f ⇒ 1 v - 1 - 1 5 = 1 1 0 ⇒ 1 v = 1 1 0 - 1 1 5 1 V = 3 - 2 3 0 ⇒ v = 3 0 cm for r , 1 . 5 3 0 = r 1 0 ⇒ r = 1 2 cm ⇒ A = π r 2 ⇒ A = π 1 2 2 A = π 4 cm 2

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