Physics Additional - Electricity Flashcards
What does alternating current mean?
It means the current is constantly changing direction
What is the mains voltage in the uk?
230 volts
What is the frequency of the AC mains supply?
50Hz
What do cells and batteries always supply?
Direct current
What does the oscilloscope do?
Shows the electricity supply
DC- straight line
What are the hazards in the home?
Long cables Frayed cables Cables in contact with something hot or wet Water near sockets Appliances without there covers on Shoving things into sockets Damaged plugs Too many plugs in one socket Lighting sockets without bulbs in
What colour is the live wire and what does it do?
Brown, alternates between positive and negative voltage
Electricity flows out through these wires
What colour is the neutral wire and what does it do?
Blue, electricity flows in and out
What colour is the earth wire and what does it do?
Yellow and green, it protects the wire and prevents people getting electrocuted
It works with the fuse to prevent fire and shocks and it carries electricity to earth
How does fusing and earthing work?
A fault develops and the live wire touches the metal casing
The case is earthed because too great a current flows through the live wire through the case and out the earth wire
This surge melts the fuse or trips the circuit breaker which cuts of the live supply and breaks the circuit
This isolates the appliance making it impossible to get an electrical shock from the case it also prevents fire and protects the wires from getting fried
The larger the current….
The thicker the cable needed to carry it
When does a socket plug not need a earth wire?
When it is double insulated, this is when it has a plastic case and no metal parts are showing
What should a three pin plug have?
The right coloured wire connected to each pin and firmly screwed in
No bare wires inside the plug
Cable grip tightly fastened over the cable outer layer
Different appliances need different amounts of electrical energy so thicker cables have less resistance and can carry more current
What are the plug features?
Metal parts are made of copper or brass because these are very good conductors
The case insulation is made of rubber or plastic and are good insulators as well as flexible
Circuit breakers V fuses
+ detect a surge in current and break the circuit by opening a switch
+ can be reset by putting the switch back in place unlike a fuse which melts and has to be replaced
- more expensive
How does a residual current circuit breaker work?
Same current flows through the live and neutral wires
When someone touches the live wire they will be earthed
The neutral wire now has less current then the live wire
The breaker detects the difference and shuts of power by opening a switch
What are the advantages of a residual circuit breaker?
Much faster than fuses this makes them safe
Work for small current changes this makes them very effective at preventing electrocution
What happens when current passes through a resistor?
It produces heat when a current flows through
As you increase current heat increases to
Also when you increase voltage your increasing the amount of current pushed through therefore heat increases
How does a filament bulb work?
Passing a current through a thin wire heats it so it glows
How does static electricity work?
When insulating materials are rubbed together negatively charged electrons will be scrapped off and dumped on to the other material
Positive static charge on one and negative static charge on the other
Opposites attract and therefore they attract small objects when placed near them
Like forces …
Repel and opposites attract
As they get further away the forces get bigger
What do ammeters do?
Measure the current in amps
Are amp meters placed in series or parallel?
Series
What does a voltmeter do?
Measures potential difference in volts
Is a voltmeter placed in series or parallel?
Parallel
What is potential difference?
The driving force that pushes the current around
What is current?
The flow of electrical charge around the circuit
- it will only flow through a component if there is PD across that component
Describe a resistor graph
The current through a resistor is directly proportional to the PD
Describe a filament light graph
As the temperature of the filament rises the resistance increases
Describe a diode graph
Current will only flow in one direction and has a high resistance in the opposite direction
Describe how resistance and temperature work together?
Resistance increases with temperature
This is because the heat causes the ions to vibrate more this makes it harder for current carrying electrons to get through the resistor so current decreases and resistance increases
How does an LED work?
It emits light when a current flows in the forward direction
They use a smaller current so are used more for lighting
How does an LDR work?
They are dependent on light to work so as light increases resistance decreases
How does a thermistor work?
Resistance decreases as temperature increases
In hot conditions resistance decreases and in coal conditions resistance increases
Explain the difference between parallel circuits and series circuits
Series - PD shared - current same - resistance adds up - cell voltage adds up Parallel - PD same - current shared
