Power and electrical appliances Flashcards
Which wire in a plug is brown?
live wire
Which wire in a plug is blue?
Neutral wire
Which wire in a plug is green and yellow?
Earth wire
Which wire in a plug is red?
None
What is the purpose of an earth wire?
to carry away electrical charge from the casing of an appliance to prevent it from giving electric shocks
Which two wires are at 0 Volts?
earth and neutral wires
What is the voltage of the live wire?
230 V
What is the function of the live wire?
it provides alternating potential difference from the mains supply
What is the function of the neutral wire?
it completes the circuit and carries away the current from the appliance
What is the core of each wire made out of?
Copper
What is AC and where is it found?
alternating current. The electrons oscillate inside the wire and create a zig-zag on an oscilloscope. Found in mains supply
What would happen if you touched the live wire?
you would get an electric shock
What is DC and where is it found?
direct current. Electrons move directly along the wire to their destination, creating a straight line on an oscilloscope. Supplied by cells and batteries
What is the frequency of the current in the UK Mains supply?
50 Hz
Why does a moving charge transfer energy?
The charge does work against the resistance of the circuit.
Kettles transfer energy in what way to which store from the mains supply?
Transfer electrically from mains supply, thermal store
Handheld fans transfer energy in what way from where to which store?
electrically from battery, kinetic store
What does the total energy transferred by an appliance depend on? Give two answers.
Its power (the energy that is transferred per second) and how long it is on for
Give the equation linking energy transferred, time and power.
Energy transferred (J)= power (W) x time (s)
E=Pt
What does a power rating tell you?
The maximum amount of energy transferred between stores each second
An appliance transfers 6000 J of energy in 30 seconds, Calculate its power.
200W
Give the equation linking charge flow, voltage, and energy transferred.
Energy transferred (J) = charge flow (C) x potential difference (V)
E = QV
An appliance with a higher voltage will supply more energy to the circuit per coulomb of charge. True or False?
True
Give the equation linking power, current, and voltage.
Power (W) = Potential difference (V) x Current (A)
P=VI
Give the equation linking power, current, and resistance.
P=I^2R
Calculate the energy transferred from a 200V source as 10,000C of charge passes.
2,000,000J or 2MJ
What two things is the National Grid made up of?
Giant network of cables and transformers that connects the power stations to the consumers
Why do most power stations not work to their full potential?
to leave spare capacity to cope with high demand.
What occasions mean that there is a high demand of electricity?
- coming home from work, school
- when its dark, cold
- popular events : sporting final on TV
Why is a high potential difference needed for the electricity being carried through the national grid?
A very high power is required, so it needs either a high voltage or high current. If the current is high, too much energy would be wasted as thermal energy before reaching its destination. It’s a lot cheaper to boost the pd up really high and help the current as low as possible.
How high does a step-up transformer take the voltage?
400,000V
How does a step up transformer work?
- It has a primary coil and a secondary coil joined with an iron core.
- Step up transformers have more turns on the secondary coil than on the primary coil, so the voltage gets increased when it passes through
- as the pd is increase by the transformer the current is decreased.
What devices bring the voltage back down to a safe level, and what voltage is this?
step down transformers, 230V
How does a step down transformer work?
They have more turns on the primary could than on the secondary.
- the pd is reduced at the local consumer and the current in increased.
How does the power in the primary coil equal the power in the secondary coil?
transformers are nearly 100% efficient
What is static electricity?
Charges which are not free to move, e.g. in insulating materials.
This causes them to build up on one place and it often ends with a spark or a shock when they finally do move
How does static electricity created?
- Ehen insulating materials are subbed together, negatively charged electrons will be scraped off one and dumped on the other
- this leave the one material electrically charged with a positive static charge and the other a equal negative static charge
Name an example of static electricity between 2 materials
Polythene and acetate rods
Acetate:
- loses electrons
- becomes positive
Andrew TATE lost followers/ lost electrons
Polythene:
- gains electrons
- become negative
What happens to the potential difference between the object and the earth when electric charge builds up on a object?
The pd increase .
The earth is a 0V
What happens if the potential difference gets large enough?
The electrons can jump across the gap between the charged object and the earth - this is a spark
- they can also jump to any earthed conductor that is nearby - which is why you can get static shocks getting out the car
- a charge builds up on the car’s metal frame and when you touch it the charge travels through you to the earth.
