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JEE Main Physics Class 12 Electric Charges and Fields Questions
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© examsnet.com
Question : 25
Total: 108
Two small spheres each of mass
10
m
g
are suspended from a point by threads
0.5
m
long. They are equally charged and repel each other to a distance of
0.20
m
. The charge on each of the sphere is
a
21
×
10
−
8
C
. The value of
a
will be ............. .
[Given,
g
=
10
m
s
−
2
]
[25 Feb 2021 Shift 2]
Your Answer:
Validate
Solution:
Given, mass of each spheres,
m
=
10
m
g
=
10
×
10
−
3
g
Length of thread
(
l
)
=
0.5
m
Separation between charges,
d
=
0.2
m
Charge of each sphere,
q
=
a
21
×
10
−
8
C
Acceleration due to gravity
(
g
)
=
10
m
s
−
2
The situation can be shown as below,
Taking component of tension (T)
T
cos
θ
=
m
g
. . . (i)
T
sin
θ
=
q
E
=
k
∣
q
2
d
2
. . . (ii)
sin
θ
=
d
∕
2
l
=
0.1
0.5
=
1
5
cos
θ
=
√
1
−
sin
2
θ
=
√
1
−
1
∕
25
=
√
24
5
∴
tan
θ
=
sin
θ
cos
θ
=
k
q
2
d
2
m
g
[using Eqs. (i) and (ii)]
⇒
1
∕
5
√
24
∕
5
=
k
q
2
d
2
m
g
⇒
1
√
24
=
9
×
10
9
×
q
2
(
0.2
)
2
×
10
×
10
−
3
×
10
⇒
q
=
√
(
0.2
)
2
×
10
−
1
√
24
×
9
×
10
9
⇒
q
=
3
×
10
−
7
C
⇒
a
21
×
10
−
8
=
30
×
10
−
8
a
=
630
© examsnet.com
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