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Three lenses L1, L2, L3 are placed co-axially as shown in figure. Focal length's of lenses are given 30 cm, 10 cm and 5 cm respectively. If a parallel beam of light falling on lens L1, emerging L3 as a convergent beam such that it converges at the focus of L3. Distance between L1 and L2 will be
- 40 cm
- 30 cm
- 20 cm
- 10 cm
The correct answer is: 20 cm
According to the problem, combination of 
and 
act a simple glass plate. Hence according to formula 
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