Question

The outer surface of a hollow sphere of aluminium of radius 50 cm is to be used as a mirror. What will be the focal length of this mirror? Which type of spherical mirror will it provide?

Answer 1

Focal length will be "25 cm". The further explanation is given below.

Explanation:

The given value is:

Radius,

r = 50 cm

As we know,

⇒  $Focal \ length=\frac{R}{2}$

On putting the values, we get

⇒                       $=\frac{50}{2}$

⇒                       $=25 \ cm$

The outermost layers including its hollow aluminum sphere can serve as something of a convex mirror.

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Answer 2

Answer:

Focal length is 25cm and it provide convex  mirror .

Explanation:

Given ,  radius of the hollow spherical = 50 cm

Let f be the focal length of the sphere .

The relation between R and f is ,

For spherical mirrors with small apertures, the radius of curvature is found to be equal to twice the focal length.

Hence , R = 2f  where R is the radius  and f  is the focal length .

From the given question we have ,

R = 50 cm

Therefore ,  f = $\frac{R}{2}$ ⇒ f = $\frac{50}{2} = 25 cm$

Hence , focal length is 25cm and it provide convex  mirror because outer surface will be bulged out  .

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