A linear object AB is placed along the axis of a concave mirror. The object is moving towards the mirror with speed U . The speed of the image of the point A is 4 U and the speed of the image of B is

Question

A linear object AB is placed along the axis of a concave mirror. The object is moving towards the mirror with speed $U$ . The speed of the image of the point A is $4 U$ and the speed of the image of B is also $4 U$ . If the center of the line AB is at a distance $L$ from the mirror then find out the length of the object.

TestHub · Accepted Answer

For a concave mirror, if x and y are object and image distances, speed of image = ( x − f ) 2 f 2 ​ × speed of object. For image speed 4 U : ( x − f ) 2 f 2 ​ = 4 gives x = 2 3 f ​ (point A) or x = 2 f ​ (point B). As the middle point happens to be the focus of the mirror, the object length comes out to L .

Physics - Geometrical Optics Question with Solution | TestHub

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