Fig. 7.1 shows a simple d.c. motor. The poles at the ends of the magnets are not labelled. end of magnet 1 axis end of magnet 2 0.15m 2.3 N LEFT split-ring commutator RIGHT 2.3 N coil brush battery [Figure 7.1]

1. (a)State the purpose of the split-ring commutator and the brushes. split-ring commutator brushes[3]
2. (b)There is an upward force shown on the left side of the coil. There is a magnetic field in the space between the ends of the magnets. State the direction of this magnetic field. Explain how you determined this direction. direction explanation[3]
3. (c)State what happens to the rotation of the coil if the magnetic field and the current in the coil are both reversed at the same time.[1]
4. (d)(i)In Fig. 7.1, the coil is horizontal. The force upward on the left side and the force downward on the right side are each 2.3 N. The distance between the sides of the coil and the axis is 0.15 m. Calculate the total moment exerted on the coil by these forces. Give the unit of your answer. moment = .................................................... unit = ....................................................[3]
5. (d)(ii)Explain why the turning effect becomes smaller as the coil becomes more vertical.[1]

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