Flashcards
Transformers
Cards in this deck (21)
- 1What can a transformer change?It can change the size of an alternating voltage - it does not change AC into DC.
- 2What do transformers need to work?They need AC to work - they do not work with DC.
- 3What is a transformer made up of?It is made up of two coils of wire wound onto a common iron core. The two coils of wire are not connected to each other in any way.
- 4What do step-up transformers do?They increase the voltage and decrease electrons flowing in wire.
They have more coils on the secondary coil than on the primary coil. - 5What do step-down transformers do?They decrease the voltage and increase the electrons in the wire.
They have fewer coils on the secondary coil than on the primary coil.
Step-down transformers are used in phone chargers, laptops and radios. - 6Why can transformers only use AC currents?Because they rely on changing magnetic field in the primary coil to induce a voltage in the secondary coil. Only AC gives the changing magnetic field that the coils need.
- 7Why can transformers not use DC?Because it will only provide a steady magnetic field and this will not induce a voltage in the secondary coil.
- 8What happens if the AC current in the primary coil of a transformer increases?As AC current increases in the primary coil, the magnetic field it produces grows and cuts through the wire of the secondary coil and induces a current (to try to cancel out the magnetic field from the primary coil).
- 9What happens if the AC current in the primary coil of a transformer falls?As the AC current in the primary coil falls, the current in the secondary coil is induced in the opposite direction to try to support the magnetic field.
- 10How can the voltage on the secondary coil be calculated from?Voltage on secondary coil can be calculated from voltage on
primary coil (and vice versa).
(Formula given in exam.) - 11What happens in the transmission lines if they carry lots of current?They get very hot, which means some power is lost.
- 12How can this power lost via the transmission lines becoming hot be reduced?It can be reduced by reducing current, which means less energy is wasted.
Therefore, step-up transformers are used to increase voltage from power stations to supply the national grid.
Step-down transformers are used in substations to reduce voltage for domestic and commercial users. - 13What does the power loss in transmission depend on?It depends on the current squared, therefore if current is halved, the power loss is only one quarter of what it was originally. The current can be reduced by increasing voltage in step-up transformer.
- 14What does the transformer equation show?It shows that the power input to a transformer is equal to the power output of the transformer.
- 15In a step-up transformer, the voltage is increased, but the current is decreased in the same proportion. How does this reduce the power lost during transmission?Because a lower current will reduce power loss during transmission, using a step-up transformer at the power station to increase the voltage has the effect of reducing the energy lost as the current flows along the power cables.
- 16Why does the step-down transformer reduce the voltage?It reduces the voltage to a safer level for consumers (but increases the current).
- 17Where is an isolating transformer used?It is used in some mains circuits, for example, a bathroom shaver socket, to make them safer.
- 18Are the two coils in an isolating transformer connected?They are not connected to each other in any way.
- 19Why is it important that the two coils in isolating transformers are not connected?It means that the user is isolated from the mains supply. This is particularly important, in bathrooms, where water is present. The isolating transformer does not affect the voltage because the two coils have the same number of turns.
- 20What does an isolating transformer have an equal number of?It has equal numbers of turns on the primary and secondary coils. This makes no difference to the voltage.
- 21What is the benefit of an isolating transformer?It is that it keeps the two halves of the circuit separate. Therefore, there is less risk of contact between live parts (connected to mains) and the earth lead (connected to body of, e.g. hairdryer). This means that the device is safer.
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- GCSE Physics (P6) Flashcards on Transformers, created by Rebecca Smith on 17/06/2017.
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- Rebecca Smith
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