An object 50 cm tall is placed on the principal axis of a convex lens. Its 20 cm tall image is formed on the screen placed at a distance of 10 cm from the lens. Calculate the focal length of the lens.
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Answered by
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Solution :
- Distance of Image from lens, (v) = 10 cm
- Height of object, (O) = 50 cm
- Height of Image, (I) = 20 cm
As we know that formula of the linear magnification;
A/q
∴ Distance of object from lens, (u) = -25 cm.
Now, using formula of the lens;
Thus;
The focal length of the lens will be 7.14 cm .
Answered by
2
Distance of the image from the lens= 10cm
Height of the object(I) = 50 cm
Height of the image(O) =20 cm
We know,
m= Height of the object(I) /Height of the image(O)
=>I/O=V/O
=>20/50=10/U
=>20U=50×10
=>20U=500
=>U=500/20
=>U=25
THEREFORE,
DISTANCE OF THE LENS(U) =-25cm
NOW,
1/F=1/V-1/U
=>1/F=1/10-1/(-25)
=>1/F=1/10+1/25
=>1/F=5+2/50
=>1/F=7/50
=>7F=50
=>F=50/7
=>F=7.14
THEREFORE, THE FOCAL LENGTH=7.14 cm
HOPE IT HELPS YOU....
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