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A beam of parallel rays is brought to focus by a plano-convex lens. A then concave lens of the same focal length is joined to the first lens. The effect of this is

a)

The focus shifts to infinity

b)

The focal point shifts towards the lens by a small distance

c)

The focal point shifts away from the lens by a small distance

d)

The focus remains undisturbed


Question ID - 152352 | Toppr Answer

A beam of parallel rays is brought to focus by a plano-convex lens. A then concave lens of the same focal length is joined to the first lens. The effect of this is

a)

The focus shifts to infinity

b)

The focal point shifts towards the lens by a small distance

c)

The focal point shifts away from the lens by a small distance

d)

The focus remains undisturbed

1 Answer - 5876 Votes

3537

Answer Key : (a) -

(a)

The combined focal length of plano-convex lens

Given,

Now when concave lens of same focal length is joined to first lens , then combined focal length

Thus, the image can be focused on infinity ( ) or focus shifts to infinity.



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