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Generation of Electrcity - Formal Homework 2: Transformers Q1. A transformer consists of three parts. (a) Identify each of the three parts on the diagram using the names below: core secondary coil primary coil 3 (b) A power station generating electricity at 16 000 volts is connected by a transformer to the National Grid where the electricity is distributed around the country at 275 000 volts What is the name given to this type of transformer? 1 (c) The transformer has 18 000 turns on the primary coil. Calculate the number of turns on the secondary coil. 3 (7) Q2. A student has two electrical power supplies. One is an a.c. supply and the other is a d.c supply. (a) Explain a.c and d.c in terms of electron flow in a circuit. (b) The student uses one of the supplies to operate a transformer. 2 (i) Which power supply should be used to operate the transformer? 1 (ii) What is the purpose of a transformer? 1 (iii) A transformer with an efficiency of 30% is used in a computer. Calculate the output power when the input power is 50 W. 3 (7) Q3. In a lab experiment a technician builds a transformer and uses electrical meters to take a number of measurements, as shown in the diagram: (a) The technician has a choice of an a.c. or a d.c. power supply. Which power supply should be used? Explain your answer. 2 (b) Calculate the electrical power in the primary circuit of the transformer. 3 (c) Calculate the electrical power in the secondary circuit of the transformer. 3 (d) Calculate the percentage efficiency of the transformer. (a) Another experiment uses a different transformer. It is 100% efficient. The primary coil has 15000 turns and the secondary coil contains 3000 turns. Calculate the secondary voltage when the primary voltage is 12 V. 3 3 (14) Total (21)