A Cylindrical glass rod with 10cm, n= 1.5 is placed in air, and one end is a convex surface. A thin lens with focal lengths f=20cm is placed in front of the glass rod, the distance between the thin lens and the glass rod is 30cm find the image of an object that is 30cm in front of the lens (Assume that the rod is long enough)
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Class 12
>>Physics
>>Ray Optics and Optical Instruments
>>Combination of Mirror and Lenses
>>One end of a glass rod of refractive ind
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One end of a glass rod of refractive index n=1.5 is spherical surface of radius of curvature R. The centre of the spherical surface lies inside the glass. A point object placed in air on the axis of the rod at the point P has its real image inside glass at the point Q (see figure). A line joining the points P and Q cuts the surface at O such that OP=2OQ. The distance PO is
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Correct option is A)
Use formula for refraction at spherical surface
v
μ
2
−
u
μ
1
=
R
μ
2
−μ
1
v
1.5
−
u
1
=
+R
1.5−1
Also, OP=2(OQ)
orOQ=
2
OP
orv=
2
−u
∴
2
−4
1.5
−
u
1
=
R
0.5
4
−3
−
u
1
=
2R
1
u
−4
=
2R
1
∴u=−8R
orPO=8R