a concave lens have a focal length of 10 cm.an object 2.5 cm high is placed 30 cm from the lens. determine the position and the size of the image
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Answer:
Given that,
Distance u=−10cm
Height h=2.5cm
Radius of curvature R=30cm
We know that, −f= 2R
−f= 2
30
f=−15cm
Now, using mirror’s formula
f
1
=
v
1
+
u
1
−
15
1
=
v
1
−
10
1
v
1
=−
15
1
+
10
1
v=30cm
Now, the magnification is
m=
u
−v
m=
10
30
m=3
We know that,
m=
h
h
′
3=
2.5
h
′
h
′
=7.5cm
Hence, the size of the image is 7.5 cm
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