A lens forms an image at 40 cm from it when the object is at 20 cm from it. What is the ratio between the image and object size?.
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Answer:
answer is 40 cm
Explanation:
Image of a distant object is formed at the focus.
The image due to first lens is formed at 20 cm. Hence, f
1
=20cm
The image due to combined lens is formed at 40/3 cm. Hence, f
eq
=
3
40
f
eq
=
f
1
+f
2
f
1
f
2
⇒f
eq
=
20+f
1
20×f
1
=
3
40
3f
1
=40+2f
1
f
1
=40cm
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