Question

When an object is placed at a distance of 50cm from concave mirror the magnification produce -1/2. Where should the object be placed to get a magnification of -1/5?

Answer 1

Using - v/u=m we get v=-25cm

From the given conditions it is clear that the image is diminished and form in front of mirror and is inverted.

M=h(image) / h(object)

If we want to make the object further diminished the object should be placed at infinite distance.

The image will form at the same place

Hence, m=-v/u where m=-1/5, v=-25cm so u will be -25×5 = - 125cm

Answer 2

Answer:

magnification by lense, m=v÷u. So -1÷2 = v ÷ -50= v = 25cm. by lense formula f= 1/v-1/u , f = -50/3. When m is -1/5 then v/u=-1/5 then v= -u/5 . Now by lense formula, -50/3 = 1/u - (-5/u) = -50/3 = 6/u so u = -18/50 cm.