Figure shows a coil of radius 2cm concentric with a coil of radius 7cm Each coil has 1000 turns with a current of 5A. In larger coil, then the current needed in the smaller coil to give the total magnetic field at the centre equal to 2mT is :
A
1.49A
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B
1.84A
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C
2.88A
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D
3.4A
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Solution
The correct option is A1.49A magnetic field due to larger coil =Nμ0i2r =1000×μ0×5×T2×7×10−2( into the plane) =44.88mT magnetic field due to smaller coil =Nμ0i2r =1000×μ0×I×T2×2×10−2 (out of the plane) =44.88mT |B|net=(44.88)−(31.4)I ∴I=1.49A