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A 4.5 cm needle is placed 12 cm away from a convex mirror of focal length 15 cm. Give the location of the image and the magnification. Describe what happens as the needle is moved farther from the mirror.

A 4.5 cm needle is placed 12 cm away from a convex mirror of focal length 15 cm. Give the location of the image and the magnification. Describe what happens as the needle is moved farther from the mirror.

Grade:11

1 Answers

Vikas TU
14149 Points
3 years ago
object size , h1 = 4.5 cm
object distance, u = –12 cm
focal length, f = + 15 cm
image distance , v = ?
magnification, m = ?
As. 1/u + 1/v = 1/f
1/v = 1/f – 1/u
Now,
putting u = –12 cm and f = +15cm , we get
1/v = 1/15 - 1/-12 = 4+5/60 = 9/60
v = 60/9 = 6.7 cm
✴image is formed 6.7 CM behind the convex mirror. it must be virtual and erect.

if h2 is size of image , then m = h2/h1 = -v/u
or,
m = h2/h1 = –(6.7)/–12 = 0.558
h2 = 0.558
h1 = 0.558 * 4.5 = 2.5 cm
 

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