    Question

# A combination of 3 convex lenses is arranged as shown. The focal length of lens I is +5 cm, lens II is +10 cm and lens III is +20 cm. Calculate the total power of the combination of the lens? A
-35 D
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B
+1 D
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C
+ 35 D
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D
+ 75 D
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Solution

## The correct option is A + 35 D Given, focal length of lens I = +5 cm, focal length of lens II = +10 cm and focal length of lens III = +20 cm. Since all the units are in cm, to convert in metres the formula for power becomes, Power of lens P=1focal length in m=100focal length in cm. Total Power = PI + PII + PIII ; P = 1f So, PI = 1005 D ; PII = 10010 D ; PIII = 10020 D Total Power of combination Pt=PI + PII + PIII ; Pt=1005 + 10010 + 10020 = 70020 Pt = + 35 D. Therefore, the total power of combination is + 35 D.  Suggest Corrections  0      Similar questions  Related Videos   Lens Formula, Magnification and Power of Lens
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