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JEE Main Physics Class 12 Ray Optics and Optical Instruments Part 1 Questions
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Question : 68
Total: 99
Light is incident from a medium into air at two possible angles of incidence (A) 20° and (B) 40°. In the medium light travels 3.0 cm in 0.2 ns. The ray will :
[Online April 9, 2013]
suffer total internal reflection in both cases (A) and (B)
suffer total internal reflection in case (B) only
have partial reflection and partial transmission in case (B)
have 100% transmission in case (A)
Validate
Solution:
Velocity of light in medium
V
med
=
3
c
m
0.2
n
s
=
3
×
10
−
2
m
0.2
×
10
−
9
s
=
1.5
m
∕
s
Refractive index of the medium
µ
=
V
air
V
med
=
3
×
10
8
1.5
=
2
m
∕
s
As
µ
=
1
sin
C
∴
sin
C
=
1
µ
=
1
2
=
30
°
Condition of TIR is angle of incidence i must be greater than critical angle. Hence raywill suffer TIR in case of
(
B
)
(
i
=
40
°
>
30
°
)
only.
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