. A step-up transformer is designed to operate from a 12 V supply and to deliver energy at 240 V. If the secondary coil ls connected to a 60 W, 240 V bulb, determine (a) the turns ratio of the transformer; (b) the primary current. (4 marks, A) . The transformer used to operate a model electric train has 1125 turns on its primary coil and 75 turns on its secondary coil. if it is plugged into a 120 V circuit, what potential difference does the model train receive? (3 marks, A)