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JEE Main Physics Class 12 Ray Optics and Optical Instruments Part 2 Questions
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© examsnet.com
Question : 49
Total: 112
In an experiment for estimating the value of focal length of converging mirror, image of an object placed at
40
cm
from the pole of the mirror is formed at distance
120
cm
from the pole of the mirror. These distances are measured with a modified scale in which there are 20 small divisions in
1
cm
. The value of error in measurement of focal length of the mirror is
1
∕
K
cm
. The value of
K
is ________.
[30-Jan-2023 Shift 1]
Your Answer:
Validate
Solution:
1
v
+
1
u
=
1
f
−
1
120
−
1
40
=
1
f
,
f
=
−
30
cm
Now,
−
1
v
2
d
v
−
1
u
2
d
u
=
−
1
f
2
d
f
Also
dv
=
du
=
1
20
cm
∴
1
20
(
120
)
2
+
1
20
(
40
)
2
=
df
(
30
)
2
On solving
df
=
1
32
cm
∴
k
=
32
© examsnet.com
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