Question

A concave lear of focal length of 20cm forms an image 1/2 the size of the object .The object distance?

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Answer 1

60cm

Explanation:

given:

focal length (f) = 20cm

image height (v) = ½u

object height (u) = ?

(1÷v) + (1÷u) = (1÷20)

(1÷(½u)) + (1÷u) = (1÷20)

(2÷u) + (1÷u) = (1÷20)

(3÷u) = (1÷20)

u = 20 × 3

u = 60cm