Question

An object is pulled out at a distance of 25cm from a spherical mirror as its image is formed behind the mirror at a distance of 5cm.Find the focal length, is it a concave or convex mirror​

Answer 1

Explanation:

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PHYSICS

Asked on December 30, 2019 byPawan Momin

When an object is placed at a distance of 25 cm from a spherical mirror, the magnification is m1. When the object is moved 15 cm away from mirror with respect to the earlier position, then magnification becomes m2. If m2m1=4, then the focal length of the mirror is :

A

−10 cm

B

20 cm

C

15 cm

D

−20 cm

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ANSWER

From the formula, v=u−fuf

Magnification m=u−v=f−uf

From the question, 

For first case, object distance u1=−25cm

After the object is moved 15 cm away from the mirror, new object distance becomes  u2=−40cm

∴  m2m1=f−u1f−u2=4

Or  f+25f+40=4

Or  3f=−60 cm

Answer 2

Answer:

Answer: Focal length is 6.25cm and the mirror is convex in nature.