Question

If the radius of curvature of a lens is 30cm , then what is its focal length​

Answer 1

Answer:

focal length is always equal to half the radius of the curvature of a lens

therefore if the focus lies on the centre of the radius of curvature

if the radius of curvature is 30 cm then the focal length is 15 centimetre

Answer 2

Answer:

• Focal length = 15cm

Explanation:

Correct Question:

If the radius of curvature of a mirror is 30cm , then what is its focal length

Given that,

• The Radius of the curvature of a mirror is 30cm.

To find:

• The focal length of the mirror

$\begin{gathered}\bf{\large{\underline{ Relation\:between\:r\:and\:f: }}} \\\end{gathered}$

⠀⠀⠀⠀⠀ $\begin{gathered}\underline {\boxed {\frak{ f = \dfrac{r}{2}}}}\\\end{gathered}$

$\begin{gathered}\underline {\bf{\star\:On\:Applying\:the\:formula:}}\\\end{gathered}$

⠀⠀⠀⠀⠀ $\begin{gathered}\implies \rm{f = \dfrac{30}{2}}\\\end{gathered}$

⠀⠀⠀⠀⠀$\begin{gathered}\underline {\boxed{\pink{ \mathrm { f = 15\: cm}}}}\:\bf{\bigstar}\\\end{gathered}$

Note:

• f = Focal length

• r = Radius of the curvature