Question

a converging lens has a focal length of 20cm calculate at what distance from the lens will and image be formed if the object is kept at a distance of 45 CM in front of the lens find the magnification justify with a ray diagram​

Answer 1

Answer:

The magnification of -1 is possible in only convex lens. When the object is moved 20 cm towards the lens, so the new object distance will be = 30 cm - 20 cm = 10 cm.

Explanation:

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Answer 2

GIVEn

a converging lens has a focal length of 20cm if the object is kept at a distance of 45 cm in front of the lens

TO FINd

find the image distance , magnification and justify with a ray diagram

SOLUTIOn

• Focal length (f) = + 20cm
• Object distance (u) = - 45cm
• Image distance (v) = ?

Apply lens formula

$\implies\sf \dfrac{1}{v}-\dfrac{1}{u}=\dfrac{1}{f} \\ \\ \\ \implies\sf \dfrac{1}{v}-\dfrac{(-1)}{45}=\dfrac{1}{20} \\ \\ \\ \implies\sf \dfrac{1}{v}=\dfrac{1}{20}-\dfrac{1}{45} \\ \\ \\ \implies\sf \dfrac{1}{v}=\dfrac{9-4}{180} \\ \\ \implies\sf \dfrac{1}{v}=\dfrac{5}{180} \\ \\ \\ \implies\sf v = 36cm$

Now , Magnification

$\implies\sf m=\dfrac{v}{u}=\dfrac{h_i}{h_o} \\ \\ \\ \implies\sf m=\dfrac{v}{u} \\ \\ \\ \implies\sf m=\dfrac{-36}{45} \\ \\ \\ \implies\sf m= -0.8$