1.1. Figure 1 shows a section of a horizontal copper wire carrying a current of 1.3 A.

A horizontal uniform magnetic field of flux density B is applied at right angles to the wire in the direction shown in the figure. 

Figure 1

State the direction of the magnetic force that acts on the moving electrons in the wire as a consequence of the current and explain how you arrive at your answer.

1.2. Copper contains 8.4 × 10²⁸ free electrons per cubic metre. The section of wire in Figure 1 is 125 mm long and has a cross-sectional area of 2.8 × 10^–5 m². 

Show that there are about 3 × 10²³ free electrons in this section of wire.

1.3. With a current of 1.3 A, the average velocity of an electron in the wire is 3.5 × 10^–6 m s^–1 and the average magnetic force on one electron is 1.8 × 10^–25 N.

Calculate the flux density B of the magnetic field.

1.4. The direction of the magnetic field changes such that the weight of the wire is supported by the magnetic force that acts upon it. 

Calculate the minimum value of the flux density of the magnetic field in which the wire should be placed.

Density of copper = 8.9 × 10³ kg m^–3