Between which two points related to a concave mirror should an object be placed to obtain on a screen an image twice the size of the object.

Here by mirror equation we have

1/v + 1/u = 1/f

Let the object needs to be placed at a distance x from the pole

Again we need m = -v/u = 2 because image must be formed having twice the height of the object.

x = -u

v/x = 2

=> x = v/2

1/v + 1/u = 1/f

Thus

1/v + 1/x = 1/f

=> 1/v + 2/v = 1/f

=> v = 3f

x = v/2

=> x = 3f/2

=> x = 1.5f

This means f<x < 2f

=> f<x<r

So image must be placed between F and C

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 between c and f

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BETWEEN C(CENTRE OF CURVATURE) & F(PRINCIPAL FOCUS) THE OBJECT SHOULD BE PLACED TO OBTAIN AN IMAGE TWICE THE SIZE OF OBJECT ... 

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 To obtain an image twice the size of the object, we must place it between F (focus) and P (pole) of the mirror, or between C (centre of curvature) and F (focus).

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b/w C and F 

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