Question

The focal length of a mirror is 15 cm. The radius of curvature is
(a) 15 cm

b   30 cm

c    45 cm

d    60 cm​

Answer 1

Provided that:

• Focal length = 15 cm

To determine:

• Radius of curvature

Solution:

• Radius of curvature = 30 cm

Using concept:

• Radius of curvature formula

Using formula:

• R = 2f

Where, R denotes radius of curvature and f denotes focal length.

Required solution:

»»» R = 2f

»»» R = 2(15)

»»» R = 30 cm

»»» Radius of curvature = 30 cm. Henceforth, option (b) is correct.

Additional information:

• If the magnification produced by a spherical mirror is in negative then the mirror is always “Concave Mirror.”

• If the magnification produced by a spherical mirror is in positive then the mirror is always “Convex Mirror.”

• If magnification is negative in a concave mirror then it's nature is “Real and Inverted” always.

• If magnification is positive then it's nature is “Virtual and Erect” always.

• If in the ± magnification, magnitude > 1 then the image formed is “Enlarged”.

• If in the ± magnification, magnitude < 1 then the image formed is “Diminished”.

• If in the ± magnification, magnitude = 1 then the image formed is “Same sized”.

• If the focal length is positive then the mirror is “Convex Mirror.”

• If the focal length is negative then the mirror is “Concave Mirror.” $\:$

Answer 2

Given:

Focal length of the mirror ($f$) = $15$ cm

To find:

Radius of curvature of the mirror ($R$)

Formula to be used:

$R$ = $2f$

Where $R$ denotes the radius of curvature and $f$ denotes the focal length of the mirror

Calculation:

$R$ = $2$ × $15$

$R =$ $30$ cm

Answer:

Therefore, the radius of curvature of the mirror is option b) $30$ cm