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