Question

А
A concave lenst of focal length 15 tem forms
an image 10 cm from the lens! How far is the
Object placed from the lens ? Draw the ray
diagram​

Answer 1

$\rm{ \orange{\bigstar Given \longrightarrow }}$

• $\sf{focal \ length=-15}$
• $\sf{ image \ distance =-10}$

$\rm{ \blue{\bigstar Find \longrightarrow }}$

• $\sf{Object \ distance-?}$

$\rm{ \pink{\bigstar Formula \ used \longrightarrow }}$

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

Where,

F= focal length,

v= image distance,

u= object distance

$\rm{ \red{\bigstar SoLution \longrightarrow }}$

By using mirror formula ,

$\bf{\dfrac{1}{f} = \dfrac{1}{v}+ \dfrac{1}{u} }$

put given value in the formula we get,

$\sf{ \implies \dfrac{1}{-15} = \dfrac{1}{-10} - \dfrac{1}{u} }$

$\sf{\implies \dfrac{1}{u} = \dfrac{1}{15}-\dfrac{1}{10} }$

$\sf{\implies \dfrac{1}{u} = \dfrac{1-2}{30} }$

$\sf{\implies \dfrac{1}{u} = \dfrac{-1}{30} }$

$\sf{\implies u= -30}$

$\green{\bf{\underline{\therefore Image \ distance \ is \ -30 cm.}}}$

( For Diagram refer the attachment )

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