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A long straight non-conducting string carries a charge density of 40 mC m-1. It is pulled along its length at a speed of 300 m/sec. What is the magnetic field at a normal distance of 5 mm from the moving string?

B=4.8 x 10-7 T
B=3.2 x10-7 T
B=2.5 x 10-7 T
B=5 x 10-7 T

detailed solution

Correct option is A

The moving string behaves like a current,i=40×10-6C/m(300 m/sec) =1.2×10-2 ampere   Then B=μ0i2πr=2×10-7×1.2×10-20.005 =4.8×10-7 tesla

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