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Question
Two converging lenses of unequal focal lengths can be used to reduce the aperture of a parallel beam of light without loosing the energy of the light. This increase the intensity. Describe how the converging lenses should be placed to do this.
Solution
Let the two converging lenses be L1 and L2, with focal lengths f1 and f2 respectively.
To reduce the aperture of a parallel beam of light without losing the energy of the light and also increase the intensity, we have to place the lens L2 within the focal range of L1.
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