A convex lens and a concave lens, each having same focal length of 25 cm are placed coaxially in close contact to form a combination of lenses. The power of the combination will be

25 dioptre

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50 dioptre

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Zero

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Infinite dioptre

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Solution

The correct option is C Zero
$P_{C} = P_{1} + P_{2} P_{1} \to Power of convex Lens P_{2} = \frac{100}{f (i n c m)} = \frac{100}{25} = + 4 D P_{2} \to Power of concave lens P_{2} = \frac{100}{- 25} = - 4 D P_{C} = P_{1} + P_{2} = 4 - 4 = 0$

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Similar questions

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Q. A convex lens of focal length 50 cm, a concave lens of focal length 50 cm and another concave lens of focal lens 20 cm are placed in contact. The power of this combination in dioptres will be:

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Q. An eye specialist prescribes spectacles having a combination of convex lens of focal length

40 c m

in contact with a concave lens of focal length

25 c m .

The power of this lens combination in diopters is:

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A convex lens and a concave lens, each having same focal length of 25 cm are placed coaxially in close contact to form a combination of lenses. The power of the combination will be

The correct option is C ZeroPC=P1+P2P1 →Power of convex LensP2=100f(in cm) =10025=+4DP2→ Power of concave lensP2=100−25=−4DPC=P1+P2=4−4=0

The correct option is C Zero
$P_{C} = P_{1} + P_{2} P_{1} \to Power of convex Lens P_{2} = \frac{100}{f (i n c m)} = \frac{100}{25} = + 4 D P_{2} \to Power of concave lens P_{2} = \frac{100}{- 25} = - 4 D P_{C} = P_{1} + P_{2} = 4 - 4 = 0$