a convex lens form image at distance of 60 cm from the lens having focal length 30calculate the object distance and power
Answers
Answer:
Given,
for lens 1,
Image distance, v=60cm
let object distance be u
f
1
1
=
v
1
−
u
1
f
1
1
=
60
1
+
u
1
f
1
1
=
60u
u+60
....(1)
when the lenses are combined, the image distance =v
2
=60−40=20cm
Focal length of the combination be F
F
1
=
f
1
1
+
f
2
1
=
v
2
1
−
u
1
⇒
f
1
1
+
f
2
1
=
20
1
+
u
1
⇒
60u
u+60
+
f
2
1
=
20
1
+
u
1
⇒
f
2
1
=
20u
u+20
−
60u
u+60
f
2
1
=
1200u
2
60u
2
+1200u−20u
2
−1200u
=
1200u
2
40u
2
f
2
=30cm
Explanation:
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heya buddy here is your answer
f(focal length)=+30cm (since it is a convex lens focal length is positive)
v(image distance)= +60cm
so as we know power(P)=100/f in cm
then P=100/30
P=10/3=3.33 D
now lets find u(object distance)
As we know
1/v-1/u=1/f
=>1/60-1/u=1/30
=>1/u=1/60-1/30
=>1/u=-1/60
=>u=-60 cm
the object is placed at a distance of 60 cm in front of the mirror
Hope it helps
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