20 17 Hybrid electric vehicles (HEV) use the same device both as a generator to charge the car battery and as an electric motor to support the propulsion system. A simplified diagram of the device is shown. The coil can rotate freely around the axis. magnet magnet S N axis coil *(a) Describe how the device can be used as both a generator and an electric motor. (6) .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. 21 Turn over (b) The circuit diagram shows a car battery connected to an electric motor for a HEV. The battery has an electromotive force (e.m.f.) 180 V and internal resistance 0.036 Ω. 180 V I M 0.036 Ω The motor has a maximum power of 88 kW. (i) Show that the current I drawn by the electric motor when operating at this power would be given by the equation 0.036I 2 − 180I + 88 000 = 0 (3) .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. (ii) Solving the equation above produces an answer of I = 550 A. At maximum power, the car can accelerate from rest to sixty miles per hour in under 7 s. The maximum charge capacity of the battery within this HEV is 6.1 amp-hour. Deduce whether the battery could maintain this current for up to 7 s. (2) .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. .................................................................................................................................................................................................................................................. (Total for Question 17 = 11 marks)