MAGNETIC FORCE
Force on a Current-Carrying Conductor in a Magnetic Field:
Immediately after Oersted’s discovery of electric currents producing magnetic fields and exerting forces on magnets, Ampere suggested that magnet must also exert equal and opposite force on a current-carrying conductor. When a current carrying conductor is kept in a magnetic field (not parallel to it), a force acts on it.
This force is created due to the interaction of magnetic field of the current in the conductor and the external magnetic field on the conductor. As a result of this superposition, the resultant magnetic field on one side of conductor is weaker than on the other side. Hence, the conductor experiences a resultant force in one direction.
Take a small aluminium rod XY. Suspend it horizontally by means of two connecting wires from a stand. Now, place a strong horseshoe magnet in such a way that the rod is between the two poles with the field directed upwards. If a current is now passed in the road from Y to X, we will observe that the rod gets displaced. This displacement is caused by the force acting on the current-carrying rod. The magnet exerts a force on the rod directed towards the right, with the result the rod will get deflected to the right. If we reverse the current or interchange the poles of the magnet, the deflection of the rod will reverse, indicating thereby that the direction of the force acting on it gets reversed. This shows that there is a relationship among the directions of the current, the field and the motion of the conductor.
In Activity 13.7(NCERT), how do we
think the displacement of rod XY will be affected if (i) current in rod XY is
increased; (ii) a stronger horse-shoe magnet is used; and (iii) length of the
rod XY is increased?
Answer: In this case, the displacement would vary directly as the
strength of current, strength of magnetic field and length of the conductor.
Due to this, the displacement of conductor would be increased in all the three
cases.
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