(a) Explain what is meant by a magnetic field (b)(i) Describe an experiment to show that a magnetic field exists around a straight wire carrying current (ii) Draw a labelled diagram showing the pattern and direction of the magnetic field rroduced around the wire. (Neglect the earth's magnetic field). (c) Sketch the magnetic field due to two straight parallel wires carrying current in the same direction. Indicate the neutral point in the field (d) Explain, with the aid of a labelled diagram, how a delicate magnetic material could be protected from the earth's magnetic field.
Explanation
(a) A magnetic field is a region in which a force of magnetic origin is experienced. It is usually due to the presence of magnetic flux which is a vector quantity. (b)
A straight wire carrying current is filled through a hole in a cardboard as shown. Compasses are placed round the conductor or the cardboard. The needles of the compass will be noticed to deflect in a particular direction. They all conform to a circular pattern indicating that the magnetic field around the conductor carrying current is circular or concentric in shape. When the current is reversed, the direction of the compass needle reverses as well. (c)
(d) Current in the same direction
The material is surrounded by a ring of iron. This shields the flux of the earth away from the material.
