Download Generation of Electrcity Formal homework 2

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Transcript
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)