Question

two thin convex lences of focal length 20cm and5cm respectively,are placed at a distance d if a parallel beam incident on the first lens emerges as a parallel beam from the second lens,then the value of d is?

Answer 1

The value of distance is 25 cm.

Explanation:

If the lenses of focal lengths f1 and f2 are "thin", the combined focal length f of the lenses is given by,

1 / f = 1 / f1 + 1 / f2 − d / f1 x f2

If the ray is coming parallel to the incident parallel beam, then f = ∞

Therefore

120 + 15 − d / 100 = 0

⇒ 14 − d / 100 = 0

⇒ 25 − d / 400 = 0

⇒ d =25 cm

Thus the value of distance is 25 cm.

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An object is placed at a distance of 10 cm from a convex mirror of focal length 15 cm . find the position and nature of the image ?

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Answer 2

Answer:

,

Explanation:

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