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| Numerical 06 |
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| 06. Two concentric circles of radius
2 cm and 4 cm respectively carry currents of 2A and 4A in a clockwise direction. What is the net magnetic field at the center? If the direction of current in the inner circle is reversed, what is net magnetic field at the center? |
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| Suggested solution: |
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| The figure below shows concentric circular coils and current flowing in them. |
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| B1 = magnetic field at O due to coil of radius (r1) = 2cm |
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| B2 = magnetic field at O due to coil of radius (r1) = 4cm |
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| B2 = magnetic field at O due to coil of radius (r2) = 4cm |
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Since both  are in the same
direction, the resultant field. B is also the same. |
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| If the direction of the current in the inner circle is reversed, the direction of B1 reverses. Now B1 and B2 are equal in magnitude and opposite in direction. Hence the-net magnetic field is zero. |
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