what is the focal length of a mirror which gives an image 3m away when object is placed 150 cm from it
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Answer:
According to the question:
Focal length, f=−1.5 m (Since it is a concave mirror)
Object distance, u=−40 cm=−0.4 m (Since 1 m=100 cm)
By mirror formula:
v
1
+
u
1
=
f
1
[4pt]
⇒
v
1
+
−0.4 m
1
=
−1.5 m
1
[4pt]
⇒
v
1
=
0.4 m
1
−
1.5 m
1
[4pt]
⇒
v
1
=
4 m
10
−
15 m
10
[4pt]
⇒
v
1
=
2 m
5
−
3 m
2
[4pt]
⇒
v
1
=
6 m
15−4
[4pt]
⇒
v
1
=
6 m
11
[4pt]
⇒v=0.5454 m=54.54 cm
Since v=54.54 cm which is positive, hence image is behind the mirror.
The image is formed at the distance of 54.54 cm behind the mirror and is virtual and erect.
Explanation:
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