Question

a concave mirror of focal length 20cm forms an image having twice the size of object. For the virtual position of object, the position of object will be- at. a) 25 cm. b) 40 cm. c)10 cm. d) at infinity.​

Answer 1

Answer:

10 cm

Explanation:

given f=-20cm m=+2

because the image is virtual and erect so the object is placed at a distance of 10 cm from the mirror

Answer 2

Answer = correct option is (c) 10cm

Explanation =

Focal length of concave mirror =f=20cm

Magnification =m=2

m=(-v/u)

therefore, 2=(-v/u)

hence, v=-2u...(1)

also, (1/f)=(1/v)+(1/u)

therefore, (1/f)=(1/-2u)+(1/u)

(1/f)={(-1+2)/(2u) }=(1/2u)

therefore, 20=2u

u=20/2

therefore,u=10cm, i.e. position of object is 10cm.

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