The focal length of a convex lens is 30 cm and an object is kept at 10 cm from lens .what will be the distance and nature of image?
Answers
Step-by-step explanation:
An object is placed 30 cm in front of convex lens of focal length 10 cm :
Given : u
1
=−30 cm f
1
=10 cm
From lens formula,
v
1
1
−
u
1
1
=
f
1
1
∴
v
1
1
−
−30
1
=
10
1
⟹v=15 cm
Thus image is formed at a distance of 15 cm behind the lens.
Now a concave lens of focal length f
2
is placed in contact with convex lens. so the screen has to be shifted by 45 cm further away.
Now the new image distance v
2
=15+45=60 cm
Let the focal length of combination of lens be F.
Using lens formula,
v
2
1
−
u
1
1
=
F
1
∴
60
1
−
−30
1
=
F
1
⟹F=20 cm
Focal length of combination of lenses
F
1
=
f
1
1
+
f
2
1
∴
20
1
=
10
1
+
f
2
1
⟹f
2
=−20 cm (minus sign comes as the focal length of concave lens is negative)
Answer:
given above
Step-by-step explanation:
have a look in that picture
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