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| Numerical 14 |
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| 14. A straight horizontal conducting rod of length 0.45 m and mass 60g is suspended by two vertical wires at it's ends. A current of 5.0 A is set up in the rod through the wires. |
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| (a) What magnetic field should be set up normal to the conductor for the tension in the wires to be zero? |
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| (b) What will be the total tension in the wires if the direction of the current is reversed, keeping the magnetic field same as before and neglecting the mass of the wires? |
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| Suggested solution: |
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| (a) l = 0.45m, I = 5.0 A |
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| Force required to balance the weight of the rod, |
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| F = 60 gf = 0.06 kgf = 0.06 x 9.8N = 0.588 N |
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| The above mentioned magnetic field should be applied in such a way that the force due to the magnetic field acts upwards on the rod. |
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| (b) Keeping the magnetic field same as in part (a), if the direction of current is reversed, then the force due to the magnetic field acts downwards. |
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| Now, total tension in the wires |
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| = Force due to weight of rod + Force due to magnetic field. |
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| = 0.588 N + 0.588 N = 1.176 N |
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