Question

An object 5 cm in length is held 25cm away from the converging lens(convex lens) of focal length 15cm. Draw ray diagram and find the position, size and nature of the image formed. (OR) b)An object of size 8.0 cm is placed at 36cm in front of a concave mirror of focal length is 18 cm. At what distance from the mirror should a screen be placed, so that a sharp focus image can be obtained ? Draw ray diagram and Find the size and the nature of the image.

Answer 1

Answer:

Object distance u = -25 cm.

Focal length = 10 cm

Let image distance be v

\\\frac{1}{f}=\frac{1}{v}+\frac{1}{u}\\ \frac{1}{10}=\frac{1}{v}+\frac{1}{-25}\\ \frac{1}{v}=\frac{1}{10}+\frac{1}{25}\\ v=16. 66\ cm

Position of the image is 16.66 cm on the other side of the lens.

Object size O = 5 cm.

Let the image size be I

Magnification is m

\\m=\frac{v}{u}\\ \frac{I}{O}=\frac{16.66}{-25}\\ I=5\times -\frac{16.66}{25}\\ I=-3.33\ cm

The nature of the image is real and its size is -3.33 cm.

The formation of the image is shown in the following ray diagram

Explanation:

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