Question

An object is placed at 20c cm from the pole of a concave mirror. It forms real image at a distance of 60 cm from the pole. Find the focal length of the concave mirror?

Answer 1

$\huge \fcolorbox{red}{pink}{Solution :)}$

Given ,

By sign convention ,

• The object distance (u) from pole of concave mirror is - 20 cm

• The image distance (v) from pole of concave mirror is 60 cm

We know that , the formula of mirror is given by

$\large \sf \fbox{ \frac{1}{f} = \frac{1}{v} + \frac{1}{u} }$

Substitute the known values , we get

$\sf \mapsto \frac{1}{f} = \frac{1}{60} + ( - \frac{1}{20}) \\ \\ \sf \mapsto \frac{1}{f} = \frac{20 - 60}{1200} \\ \\ \sf \mapsto f = - \frac{1200}{40} \\ \\ \sf \mapsto f = - 30 \: cm$

Hence , the focal length of concave mirror is -30 cm

______________ Keep Smiling ☺

Answer 2

$\huge\underline{\underline{\bf \orange{Question}}}$

An object is placed at 20c cm from the pole of a concave mirror. It forms real image at a distance of 60 cm from the pole. Find the focal length of the concave mirror

$\huge\underline{\underline{\bf \orange{Solution-}}}$

$\large\underline{\underline{\sf Given:}}$

• Object distance (u) = - 20 cm
• Image distance (v) = 60cm

$\large\underline{\underline{\sf To\:Find:}}$

• Focal lenght of concave mirror (f)

✪$\large{\boxed{\bf \blue{\dfrac{1}{f}=\dfrac{1}{v}+\dfrac{1}{u}} }}$

$\implies{\sf \dfrac{1}{f}=\dfrac{1}{60}+\left(-\dfrac{1}{20}\right) }$

$\implies{\sf \dfrac{1}{f}=\dfrac{1}{60}-\dfrac{1}{20} }$

$\implies{\sf \dfrac{1}{f}=\dfrac{20-60}{60×20} }$

$\implies{\bf \dfrac{1}{f}=\dfrac{-40}{1200}}$

$\implies{\bf \red{Focal\:Lenght(f)=-30cm} }$

$\huge\underline{\underline{\bf \orange{Answer-}}}$

Focal lenght of concave mirror is ${\bf \red{-30cm}}$.

________________ Sagar ? :p