KnowledgeBoat Logo
|

Physics

An object is placed in front of a concave lens at a distance of 45 cm from it. If its image is formed at a distance of 30 cm from the lens, calculate the focal length of the lens.

Refraction Lens

4 Likes

Answer

(a) Given,

Object distance (u) = -45 cm

Image distance (v) = -30 cm

From lens formula,

1f=1v−1u1f=1−30−1(−45)1f=−130+1451f=−3+2901f=−190f=−901f=−90 cm\dfrac{1}{\text f} = \dfrac{1}{\text v} - \dfrac{1}{\text u} \\[1em] \dfrac{1}{\text f} = \dfrac{1}{-30}-\dfrac{1}{(-45)}\\[1em] \dfrac{1}{\text f}=-\dfrac{1}{30}+\dfrac{1}{45}\\[1em] \dfrac{1}{\text f} = \dfrac{-3+2}{90}\\[1em] \dfrac{1}{\text f} = -\dfrac{1}{90} \\[1 em] \text f = -\dfrac{90}{1}\\[1 em] \text f= - 90 \text { cm}

Answered By

2 Likes

Related Questions