Question

The radius of curvature of a spherical mirror is 20 cm. what is its focal length​

Answer 1

Answer: Radius of curvature (R) = 20 cm

Radius of curvature of the spherical mirror = 2 × Focal length (f)R = 2f

f= R/2 = 20 / 2 = 10

Therefore, the focal length of the spherical mirror is 10 cm.

Answer 2

Given :-

The radius of curvature of a spherical mirror = 20 cm

To Find :-

The focal length of the mirror.

Analysis :-

Here we are given with the radius of curvature of a spherical mirror.

In order to find the focal length substitute the given values such that radius is equal to twice the focal length.

Solution :-

We know that,

• r = Radius
• f = Focal length

Using the formula,

$\underline{\boxed{\sf Radius=2 \times Focal \ length}}$

Given that,

Radius (r) = 20 cm

Substituting their values,

⇒ 20 = 2 × f

⇒ f = r/2

⇒ f = 20/2

⇒ f = 10 cm

therefore, the focal length of the mirror is 10 cm.