Question

If the focal length of the concave mirror is 20,then the radius of curvature is:-. a)+10cm b)-10cm c)+40cm d)-40cm

Answer 1

Answer:

• Correct option is (d) - 40 cm

Explanation:

Given,

• Focal length of Concave mirror, f = -20 cm

( focal length of concave mirror is always negative )

we need to find,

• Radius of curvature of Concave mirror, R = ?

As we know,

• R = 2 f

[ Where R is radius of curvature of mirror and f is focal length of mirror ]

so,

Using formula

→ R = 2 f

→ R = 2 ( - 20 )

→ R = - 40 cm

therefore,

• Radius of curvature of the concave lens of focal length -20 cm is -40 cm .

Hence,

OPTION ( d ) - 40 cm is correct.

Answer 2

⭐ Given :-

• Focal Length Of A Concave Mirror = -20cm. (Focal Length Is always Negative.)

⭐ To Find :-

• Radius Of Curvature.

⭐ Solution :-

Use Formula,

R = 2f.

Here,

R = Radius,

f = Focal Length.

We can use this Formula to find out radius.

So,

➨ R = 2( - 20 ).

➨ R = 2 × -20.

➨ R = -40cm.

Hence, Answer is Option [D] -40 cm.