Two lenses in contact form an achromatic lens, Their focal lengths are in the ratio 2:3. Their disperive powers must be in the ratio of
A
1:3
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B
2:3
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C
3:2
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D
3:1
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Solution
The correct option is B2:3 Given, f1f2=23
we know that the condition of achromatic is ω1f1+ω2f2=0 ⇒∣∣∣ω1f1∣∣∣=∣∣∣−ω2f2∣∣∣ ⇒∣∣∣ω1ω2∣∣∣=∣∣∣−f1f2∣∣∣=∣∣∣−23∣∣∣=23=2:3