(a) A long straight vertical wire carries a current I. The wire passes through a horizontal card EFGH, as shown in Fig. 8.1 and Fig. 8.2. [Figure 8.1] [Figure 8.2 (view from above)]

1. (a)On Fig. 8.2, draw the pattern of the magnetic field produced by the current-carrying wire on the plane EFGH.[3]
2. (b)(i)Two long straight parallel wires P and Q are situated a distance 3.1 cm apart, as illustrated in Fig. 8.3. [Figure 8.3] The current in wire P is 6.2 A. The current in wire Q is 8.5 A. The magnetic flux density B at a distance x from a long straight wire carrying current I is given by the expression B = μ₀I / 2πx where μ₀ is the permeability of free space. Calculate: the magnetic flux density at wire Q due to the current in wire P[2]
3. (b)(ii)Calculate: the force per unit length, in N m⁻¹, acting on wire Q due to the current in wire P.[2]
4. (c)The currents in wires P and Q are different in magnitude. State and explain whether the forces per unit length on the two wires will be different.[2]

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