Question

If the radius of curvature of concave mirror is 20 metre its focal length is​

Answer 1

So, focal length = 21× radius of curvature = 21×20 cm = 10 cm.

Explanation:-

Radius of curvature = 2 x focal length.

So, focal length =

2

1

× radius of curvature =

2

1

×20 cm = 10 cm

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Answer 2

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Radius of curvature = 2 x focal length

$\sf{so \: focal \: length = \frac{1}{2} \times radius \: of \: curvature }$

$\sf{ \frac{1}{2} \times 20 = 10cm}$

$\sf \color{magenta}{❥Hope \: it \: helps \: you....}$