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JEE Main 8 Apr 2019 Paper 1 Solved Paper
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© examsnet.com
Question : 15
Total: 91
A thin strip 10 cm long is on a U shaped wire of negligible resistance and it is connected to a spring of spring constant 0.5 Nm
−
1
(see figure). The assembly is kept in a uniform magnetic field of 0.1 T. If the strip is pulled from its equilibrium position and released, the number of oscillations it performs before its amplitude decreases by a factor of e is N. If the mass of the strip is 50 grams, its resistance 10 Ω. and air drag negligible, N will be close to :
5000
1000
50000
10000
Validate
Solution:
Force on oscillating wire if it’s speed v is
F
=
B
2
l
2
V
R
=
b
V
Time period T is
=
25
√
m
k
No. of oscillations is
t
T
and tis given by
t
=
2
m
b
© examsnet.com
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