a. The size of the force acting on a wire carrying a current in a magnetic field is proportional to the size of the current in the wire. With the aid of a diagram, describe how this can be demonstrated in a school laboratory.
b. At a certain point on the Earth’s surface, the horizontal component of the Earth’s magnetic field is 1.6 × 10⁻⁵ T. A piece of wire 3.0 m long and weight 0.020 N lies in an east–west direction on a laboratory bench. When a large current flows in the wire, the wire just lifts off the surface of the bench.
i. State the direction of the current in the wire.
ii. Calculate the minimum current needed to lift the wire from the bench.