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प्रश्न
A concave lens of focal length 15 cm forms an image 10 cm from the lens. How far is the object placed from the lens? Draw the ray diagram.
उत्तर
Focal length f = −15 cm ...(negative due to sign convention)
Image distance v = −10 cm ...(negative due to sign convention)
Object distance u = ?
Applying the lens formula:
`1/"f" = 1/"v" - 1/"u"`
⇒ `1/"u" = 1/"v" - 1/"f"`
⇒ `1/"u" = 1/(-10) - 1/(-15)`
⇒ `1/"u" = -1/10 + 1/15`
⇒ `1/"u" = (-3 + 2)/30`
⇒ `1/"u" = (-1)/30`
u = − 30 cm
The object should be placed at a distance of 30 cm from the concave lens and on the left side.
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