Question
An object is placed at a distance of 30 cm from the lens. Its image is formed at a distance of 10 cm on the same side of the lens. Find the focal length of the lens used.
Answer: Option D
:
D
Given:
Image distance v=−10 cm
Object distance u=−30 cm
(Using the sign conventions)
Let focal length of the lens be f.
Using the lens formula,
1f=1v−1u
1f=(1−10)−(1−30)
f=−15 cm
Here, negative sign for focal length shows that the lens is concave.
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:
D
Given:
Image distance v=−10 cm
Object distance u=−30 cm
(Using the sign conventions)
Let focal length of the lens be f.
Using the lens formula,
1f=1v−1u
1f=(1−10)−(1−30)
f=−15 cm
Here, negative sign for focal length shows that the lens is concave.
Was this answer helpful ?
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