A convex lens A of focal length 20cm and a concave lens G of focal length 5cm are kept along the same axis with the distance d between them. If a parallel beam of light falling on A leaves B as a parallel beam, then distance d in cm will be
25cm
15cm
30cm
50cm
A
25cm
B
30cm
C
15cm
D
50cm
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Solution
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P=1f1=1f2−df1f2 0=120−15−d20(−5) d100=15−120=4−120=320 or d=15cm.
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