Magnetic field due to currentHard
Question
A nonconducting disc having uniform positive charge Q, is rotating about its axis with uniform angular velocity ω. The magnetic field at the centre of the disc is -
Options
A.directed outward
B.having magnitude
C.directed inwards
D.having magnitude 
Solution
Charge per unit area = 
Charge on elemental ring,
dQ =
2πrdr = 
∴ B at centre =
=
Charge on elemental ring,
dQ =
2πrdr = ∴ B at centre =
=
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