Question

a 4.5 CM needle is placed 12 cm away from convex mirror of focal length 15cm .Give the location of image​

Answer 1

Here,

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

☆As the needle is moved further from the mirror, image moves away from the mirror till it is at focus F of the mirror the size of the image goes on decreasing.

Hope it helps u..........✌✌

Answer 2

Answer:

Given :- h = 4.5 cm , u = - 20 cm , f = 15 cm .

To find :- v = ? , m = ?

Solution :-

By mirror formula ;-

1 / v + 1 / u = 1 / f

1 / v = 1 / 15 - 1 / - - 20

1 / v = 1 / 15 + 1 / 20

1 / v = 4 + 3 / 60 = 7 / 60

v = 60 / 7 cm = 8.5 cm

m = - v / u = h' / h

m = - 60 / 7 / - 20

m = 3 / 7 = 0.4