Fig. 7.2 shows a circuit diagram of a step-down transformer.
Fig. 7.2
The mains voltage supplied to the transformer is 240 V. The output power of the transformer is 45 W. The transformer is 100% efficient.
Calculate the input current to the transformer.
input current =
Draw a labelled diagram of a step-down transformer. On the labels, state a suitable material for each of the components.
A transformer consists of two coils of wire wound on a core.
Suggest the material from which the two coils are made. State the reason for using this material.
material
reason
Suggest the material from which the core is made. State the reason for using this material.
material
reason
Fig. 8.1 represents the system of transmission of electrical energy from a power station to a home that is a long distance away.
Fig. 8.1
State the difference between transformer X and transformer Y .
Explain why a very high voltage is used for transmission over large distances.
A transformer has 400 turns on the primary coil connected to the 240 V mains supply.
There are two secondary coils to serve different parts of a television. Secondary coil 1 has 2500 turns and secondary coil 2 has 20 turns.
Which row is correct?
p.d. across secondary coil 1/V
p.d. across secondary coil 2/V
12
3.2
1500
12
4200
12
4200
33
Fig. 7.2 shows a circuit diagram of a step-down transformer.
Fig. 7.2
Draw a labelled diagram of a step-down transformer. On the labels, state a suitable material for each of the components.
Fig. 8.1 represents the system of transmission of electrical energy from a power station to a home that is a long distance away.
Fig. 8.1
State the difference between transformer X and transformer Y .
Transformers are used in the transmission of electrical power to houses.
Which type of transformer is used at the power station prior to connection to the power lines and which type is used prior to delivery to the houses?
power station
before houses
step-down
step-down
step-down
step-up
step-up
step-down
step-up
step-up
Fig. 10.1 shows a transformer that consists of two coils P and Q, and an iron core.
Fig. 10.1
There are 200 turns on coil P and 340 turns on coil Q.
A4.0 V a.c. power supply is connected to coil P.
A transformer is used to step up the voltage before electrical energy is transmitted over long distances.
State and explain one economic effect of transmitting electrical energy at a high voltage.
Fig. 9.1 shows a mobile phone (cell phone) being charged on a wireless charging plate.
Fig. 9.1
When the charging plate is switched on, there is an alternating current (a.c.) in the primary coil. A secondary coil is in the mobile phone.
Explain how a current is produced in the secondary coil.
Fig. 7.2 shows a circuit diagram of a step-down transformer.
Fig. 7.2
The mains voltage supplied to the transformer is 240 V. The output power of the transformer is 45 W. The transformer is 100% efficient.
Calculate the input current to the transformer.
input current =
Electricity is transmitted at high voltage.
Explain why a high voltage increases the efficiency of transmission even with thinner wires.
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