Question

An object is placed in front of a convex lens of focal length 5cm and a virtual image is formed at a distance of 25cm. Find the magnification and draw the ray diagram.

Answer 1

GIVEn

An object is placed in front of a convex lens of focal length 5cm and a virtual image is formed at a distance of 25cm.

TO FINd

Find the magnification and draw the ray diagram.

SOLUTIOn

• f = + 5 cm
• v = - 25 cm
• m = ?

Apply lens formula

$\implies\tt \dfrac{1}{v}-\dfrac{1}{u}=\dfrac{1}{f} \\ \\ \implies\tt \dfrac{-1}{25}-\dfrac{1}{u} =\dfrac{1}{5} \\ \\ \implies\tt \dfrac{1}{u}=\dfrac{-1}{25}-\dfrac{1}{5} \\ \\ \implies\tt \dfrac{1}{u}=\dfrac{-1-5}{25} \\ \\ \implies\tt \dfrac{1}{u}=\dfrac{-6}{25} \\ \\ \implies\tt u = -4.1 cm$

Now, Magnification

$\implies\tt m=\dfrac{v}{u} \\ \\ \implies\tt m=\dfrac{-25}{-4.1} \\ \\ \implies\tt m = 6.09$

Nature of image

• Nature = Virtual and erect
• Size = Enlarged
• Position = same side of lens as a object