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Two lenses of local lengths 0.20m and 0....

Two lenses of local lengths 0.20m and 0.30m are kept in contact. Find the focal length of the combination. Calculate power of two and combination.

Text Solution

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Here: `f_1 =0.20m,f_2=0.30m,f=?, P_(1)=?,P_(2)=?,P=?`
The effective focal length of the combination is
`1/f=1/(f_(1) ) + 1/(f_2)`
`= (1)/(0.20) + 1/(0.30)`
f = 0.12 m
power of lens is P = 1/f
`P_(1) = 1/f_(1) = 1/(0.20) = 5D`
`P_(2) = 1/f_(2) = 1/(0.30) = 3.333D`
`P = 1/f = 1/(0.12) = 8.333 D`
`P = P_(1) +P_2`
`= 5 + 3.333`
`= 8.333` D
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