Question

A student did an experiment with a convex lens. He put an object at different distances 25 cm, 30 cm, 40 cm, 60 cm and 120 cm from the lens. In each case he measured the distanced the distance of the image from the lens. His results were 100 cm, 24 cm, 60 cm, 30 cm and 40 cm, respectively. Unfortunately his results are written in wrong order.; (a) Rewrite the image distance in the correct order.; (b) What would be the image distance if the object distance was 90 cm?; (c) Which of the object distances gives the biggest image?; (d) What of the focal length of this lens?

Answer 1

Answer:

The image distance which will be in correct order will be 100cm, 60cm , 40cm,

30cm, 24cm.

While, we know that when u= -25cm and v=100cm.

The equation 1/v - 1/u = 1/f. So, on substituting the values from the given question we will get that 1/100 - 1/(-25) = 1/f which on solving we will get the value of f to be 20cm.

Now when u = -90cm.

1/v - 1/u = 1/f.

1/v - 1/(-90) = 1/20.

Which on solving we will get the value of v to be 25.7 cm.

So, the object distance which give the biggest image is 25cm and the focal length of lense is 20cm.

Answer 2

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