The charged currents in the outer conducting regions of the earth's core are thought to be responsible for earth's magnetism. What might be the battery' (i.e., the source of energy) to sustain these currents?

A telephone cable at a place has four long straight horizontal wires carrying a current of 1.0 A in the same direetion east to west. The earth's magnetic held at the place is 0.39 G, and the angle of dip 35^@. The magnetic declination is nearly zero. What are the resultant magnetic felds at points 4.0 cm below the cable?

A toroid has a non ferromagnetic core of inner radius 25 cm and outer radius 26 cm around which 3500 turns of wire are wound. If the current in the wire is 11A, what is the magnetic field (a) outside the toroid? (b) inside the core of the toroid? (c) in the empty space surrounded by the toroid?

The earth's surface has-a negative surface charge density of 10^(-9) Cm^(-2) . The potential difference of 400kV between the top of the atmosphere and the surface results in a current of only 1800A over the entire globe. If there were no mechanism of sustaining atmospheric electric field, how much time would be required to neutralize the earth's surface charge? Take radius of earth = 6.37xx 10^(6) m.

The horizontal component of the earth’s magnetic field at a certain place is 3.0 ×10^(-5) T and the direction of the field is from the geographic south to the geographic north. A very long straight conductor is carrying a steady current of 1A. What is the force per unit length on it when it is placed on a horizontal table and the direction of the current is (a) east to west, (b) south to north?