    Question

# 6. a.An object 4 cm in size is placed at a distance of 25 cm from a concave mirror of focal length 15 cm. Find the position, nature and height of the image. b A converging mirror forms a real image of height 4 cm, of an object of height 1 cm placed 20 cm away from the mirror. Calculate the image distance. What is the focal length of the mirror?

Open in App
Solution

## Given that f = -15 cm; u = -25 cm ; ho= 4 cm; v = ? The mirror formula is 1/f = 1/u + 1/v = 1/-15 = 1/-25 + 1/v 1/v = 1/25 - 1/15 1/v = (3-5)/ 75 =-2/ 75 v =-37.5 cm The screen should be placed 37.5 cm from the pole of mirror and the image is real. Magnification, m = -v/u =hi/ho= hi / 4 = 37.5 / 25 hi = (37.5 / 25 )x 4 = -6 cm So the image is enlarged and inverted. b)# Converging mirror is actually concave mirror! hi = -4cm(real and inverted.) ho = 1cm u=-20cm (a) v=? hi/ho=-v/u where, hi=height of the image ho=height of the object v=distance of the image from the mirror u=distance of the object from the mirror -4/1=-v/-20 4 = v/20 v = -80cm Let focal length of the mirror to be 'f' 1/f = 1/v + 1/u 1/f = 1/-80 + 1/(-20) 1/f = 1/-80 - 1/ 20 1/f = -5/80 f = -80/5cm = -16 cm  Suggest Corrections  30      Similar questions  Related Videos   Mirror Formula and Magnification
PHYSICS
Watch in App  Explore more