What is current?
- the flow of electrical charge around a circuit (flow of electrons)
- measured in amps, A
- more charge passes round a circuit when a higher current flows
What is voltage?
- driving force that pushes current round
- measured in volts, V
What is resistance?
- anything in a circuit that slows the flow down
- measured in ohms
How does voltage affect current?
- current only flows through a component if there is a voltage across that component (unless the component is a superconductor)
- increasing voltage means more current flows
How does resistance affect current?
–increasing resistance means less current flows (or more voltage needed to keep to same current flowing)
How are circuits like the flow of water in pipes?
- current is flow of water
- voltage the force provided by pump which pushes water out/pressure
- resistance is any type of constriction in the flow that works against the pressure
- turning up pump will provide more force (voltage), so the flow will increase
- more constrictions (resistance), decreases the flow (current)
What happens if you break the circuit?
-current stops as current only flows in a circuit if there is a complete loop for it to flow around
What are the components of a plug and there function?
- live wire: orange, carries the voltage. It alternates between high positive and negative voltage of about 230 V
- neutral wire: blue, completes circuit (electricity flows in through live wire and out through neutral wire). Always at 0 V
- earth wire (and fuse or circuit breaker):green and green, for safety and work together
What has to be earthed and why?
- all appliances with metal casing
- to reduce danger of electric shock
- earthing means they must be attached to an earth wire
- earthed conductors never become live (earth wire stops appliances becoming live)
How do fuses work?
1-if a fault causes the live wire to touch the metal case then the case is earthed: a big current flows through the live wire, through the case and out down the earth wire
2-surge in current ‘blow’ the fuse and cause the wire inside it to melt, cutting off the live supply because it breaks the circuit
3-this isolates the appliance making it impossible to get an electric shock from case
How can you use a test circuit to measure resistance?
1-as you vary the variable resistor it alters the current flowing through circuit
2-allowing you to take several pairs of reading from ammeter and voltmeter
-ammeter measures the current through the component, it’s placed in series (in line) with the other components
-voltmeter measures voltage across the component, placed parallel to component being tested
What are variable resistors?
-resistor whose resistance can be changed
What resistor has the best resistance?
- thinner wires have more resistance, as there is less space for electric charges to move through
- longer wires have more resistance, as there us more material for the electric charge to flow through, increasing resistance
How does voltage, current and resistance change across a resistor?
-increasing voltage across a resistor increases current as well, and resistance decreases
What does blowing a fuse do that is beneficial?
- stops the flex (part of the plug, long wire coming from plug) overheating, which could cause a fire
- preventing further damage of appliance
What is a circuit breaker?
-works like a fuse but can reset after it ‘trips’ and used again
What should a fuse’s rating be and why?
- as near as possible but just higher than the normal operating current
- a fuse much higher wouldn’t blow when the live wire touches the case or a when a fault developed
What is the proper name of voltage?
-potential difference, pd
What are variable resistors good at and how does it do it work?
- altering the current flowing through a circuit
- turn resistance up , current drops
- turn down resistance, current drops
How do old variable resistors work?
- huge coils of wire with a slider on them
- as you move the slider, the length of wire that has current through it changes
