Question

A mirror is formed by cutting part of sphere .The sphere has a radius of 10 cm if the volume of Sphere is made 27 times what will be the new focal length of the mirror formed​

Answer 1

Given : A mirror is formed by cutting a part of sphere. The sphere has a radius of 10cm .

now the volume of sphere is made 27 times of its initial.

To find : The new focal length of the mirror formed.

solution : when radius of sphere is 10cm.

focal length of mirror would be , f = r/2 = 5 cm

now volume of sphere is made of 27times.

i.e., volume of new sphere = 27 × volume of sphere initially

⇒4/3 πR³ = 27 × 4/3 π (10cm)³

⇒R³ = (3)³ × (10cm)³ = (30cm)³

⇒R = 30cm

so new focal length of the mirror formed, f' = R/2 = 30/2 = 15cm

Therefore the new focal length of the mirror formed is 15 cm

Answer 2

Answer:

The radius of curvature of the mirror =24cm.

Thus the focal length

=24cm/2

=12cm.

Explanation: