A concave lens of focal length 20 cm placed in contact with a plane mirror acts as a convex mirror of focal length

10 cm

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40 cm

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60 cm

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20 cm

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Solution

The correct option is A 10 cm
1/F=2/f+1/f_m

f_m = infinity

then F=f/2

20/2 = 10

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Focal length of convex lens is 20 cm, focal length of concave mirror is 30 cm. And the separation between lens and mirror is 90 cm. If the object is placed 60 cm before lens, find out position of image formed by concave mirror?

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A concave lens of focal length 20 cm placed in contact with a plane mirror acts as a convex mirror of focal length

The correct option is A 10 cm1/F=2/f+1/fm fm = infinity then F=f/2 20/2 = 10

The correct option is A 10 cm
1/F=2/f+1/f_m

f_m = infinity

then F=f/2

20/2 = 10