A double convex lens forms a real image of an object on a screen which is fixed. Now the lens is given a constant velocity v = 1 ms − 1 along its axis and away from the screen. For the purpose of form

Question

A double convex lens forms a real image of an object on a screen which is fixed. Now the lens is given a constant velocity v = 1 ms − 1 along its axis and away from the screen. For the purpose of forming the image on the screen, find the velocity of the object at the instant its size is double the size of the image.

TestHub · Accepted Answer

Let us take the lens to be stationary and the screen moving with velocity v away from the lens. Velocity of the object with respect to the screen: v OS ​ = v − m 2 v ​ . As m = 2 1 ​ , v OS ​ = 1 − ( 1/2 ) 2 1 ​ = 1 − 4 = − 3 m/s, i.e. 3 m/s towards the screen.

Physics - Geometrical Optics Question with Solution | TestHub

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