Question

A teacher gives a convex lens and a concave mirror of focal length of
20 cm each to his student and asks him to find their focal lengths by
obtaining the image of a distant object. The student uses a distant tree as
the object and obtains its sharp image, one by one, on a screen. The
distances dy and d2 between the lens/mirror and the screen in the two
cases and the nature of their respective sharp images are likely to be
(a)
(20 cm, 40 cm) and (erect and erect)
(b)
(20 cm, 40 cm) and (inverted and inverted)
(c)
(20 cm, 20 cm) and (inverted and inverted)
(d)
(20 cm, 40 cm) and (erect and inverted)
Give reason for your answer.​

Answer 1

Explanation:

C. 20cm,20cm

because the object is at infinity.So the image is at focus

v=f

f=20cm

Therefore,V=20cm

When object is at infinity,the image is of point sized and inverted.

Hope it helps you

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