Question

If a concave mirror has a focal length of 10cm find the two positions where an object can be placed to give in each case and image twice the height of the object.

Answer 1

f of concave mirror =-10cm

case 1

image is real and magnification is -2

1/f=1/v-1/u

m=-v/u

-2=-v/u

v=2u

now using mirror formula

1/-10=1/2u+1/u

1/-10=/2u

u=-15

Hence object should be placed at a distance of 15 cm in front of the concave mirror

Case 2

m=-v/u

v=-2u

using mirror formula

1/f=1/v+1/u

1/-10=1/-2u+1/u

-1/10=1/2u

u=-5cm

Hence object should be at a distance of 5 cm in front of the concave mirror

Answer 2

Answer:

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