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KCET 2020 Physics Solved Paper
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© examsnet.com
Question : 11
Total: 60
Three polaroid sheets
P
1
,
P
2
and
P
3
are kept parallel to each other such that the angle between pass axes of
P
1
and
P
2
is
45
°
and that between
P
2
and
P
3
is
45
°
. If unpolarised beam of light of intensity
128
W
m
−
2
is incident on
P
1
. What is the intensity of light coming out of
P
3
?
64 𝑊𝑚
−
2
128 𝑊𝑚
−
2
0
16 𝑊𝑚
−
2
Validate
Solution:
We have unpolarised beam's intensity
I
0
=
128
w
∕
m
2
Using Malu's law we have
I
=
I
0
cos
2
θ
When beam passed from the first polaroid,
I
=
I
0
2
Again, as the angle between
p
1
and
p
2
is
45
°
, beam intensity when it will pass
p
2
would be
I
1
=
I
0
2
cos
2
45
°
=
I
0
4
And, also the angle between
p
2
and
p
3
is
45
°
, beam intensity when it will come out of
p
3
will be
I
2
=
I
0
4
cos
2
45
°
=
I
0
8
=
128
8
=
16
w
∕
m
2
© examsnet.com
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