Question

By concave mirror image of an object is obtained on the screen. If size of image is double that of object, then
find focal length of mirror. (separation between object and screen is 80 cm)​

Answer 1

Answer:

-160 cm

Explanation:

h₂ = 2h₁   [h₂ is image size and h₁ is object size]

u = -80 cm

Wkt, h₂/h₁ = -v/u

Now, by substituting h₂ value and u value,

2h₁/h₁ = -v/-80

⇒ 2 = v/80

⇒ 160 = v

∴ v = 160 cm

Substituting the values of u and v in mirror formula

1/f = 1/u + 1/v

1/f = -1/80 + 1/160

By taking LCM

1/f = -2/160 + 1/160

1/f = -1/160

∴ f = -160 cm

Hope this helped!