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If two lenses of +5 dioptres are mounted...

If two lenses of `+5` dioptres are mounted at some distance apart, the equivalent power will always be negative if the distance is

A

Greater than 40 cm

B

Equal to 40 cm

C

Equal to 10 cm

D

Less than 10 cm

Text Solution

Verified by Experts

The correct Answer is:
A
Combined power-
`P = P_(1) + P_(1) - dP_(1) P_(2) = 10 - 25 ` d
for P `rarr `- ve , 25 d `gt ` 10
d `gt ` 40 cm .
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