Section 21: Electricity And Circuits Flashcards
Current
The flow of electric charge around the circuit. The current will only flow through the electrical component if there is a potential difference across the component and if the circuit is complete
Potential difference
Known as voltage. The driving force that pushes the charge around
The energy transferred per coulomb of charge that passes between 2 points in an electrical circuit
Unit of current
Amps, A
Unit of potential difference
Volts - V
Resistance
Anything that slows the flow down
Unit of resistance
Ohms
What does the current depend on
The current flowing though a component depends of the potential difference across it and the resistance of the component
______ the potential difference across a given component the ______ the ______ will be.
Higher , higher, current
The _________ the resistance the _______ the _____………_… that flows
Greater, smaller the current
How to work out charge
Charge = current X time
How to calculate energy transfer
Energy transfer = charge moved X potential difference
How to calculate potential difference
Potential difference = current X resistance
How does resistance increase with temperature
- When an electrical charge flows through a component, it has to do work against resistance
- This causes an electrical transfer of energy
- Some of this energy is transferred usefully but some of it is dissipated to the thermal energy stores of the component and the surroundings
- So when a current flows through a resistor the resistor heats up
- This is because the electors collide with the ions in the lattice that makes up the resistor as they flow through it. This gives the ions energy which causes them to vibrate and heat up.
- The more the ions vibrate, the harder it is for electrons to get through the resistor as there is more collisions. This means that for a given potential difference, the current decreases as the resistor heats up.
- If the resistor gets too hot, no current will be able to flow
Series circuits
- Only one route the current can take around the circuit
- You cannot switch lamps individually
- If one lamp fails, they will all switch off. If you remove or disconnect one component, the circuit will be broken and stop working
- The different components are connected in a line end to end between positive and negative power supplies (except for voltmeters as they connect in parallel but they don’t count as part of the circuit.
Parallel circuits
- There are junctions that allow the current to take different routes
- Each lamp can be switched separately
- Each component is separately connected to the positive and negative supply (except ammeters as they’re always in series)
Rules to design a series circuit
- More bigger supply for potential difference when more cells are in series.
- The current is the same everywhere. The size of the current depends on the total potential difference.
- The total potential difference of the supply is shared between components and it depends on its resistance.
- The total resistance of the circuit increases as you add resistors.
Rules to design a parallel circuit
- Potential difference is the same across all components
- Current is shared between beaches. The total current flowing around the circuit is equal to the total of all currents through separate components.
- There are junctions where the current either splits of rejoins. The current going into a junction has to equal the total current leaving
- The total resistance of the circuit decreases if you add a second resistor in parallel
What does the standard test circuit contain
- Ammeter and voltmeter to measure current and potential difference
- variable resistor- change current through the circuit by increasing the total resistance by increasing the variables resistors resistance lowers the current through the circuit. Which also changes the potential difference across the test component
How to use a circuit to investigate a component
- Connect the circuit. The component and the ammeter are in series which means they can be put in any order in the main circuit. Voltmeter must be parallel
- Change the resistance of the variable resistor. Measure the current through the potential difference across the component
- Take several pairs of readings from the ammeter and voltmeter at a number of different resistances
- Plot the current against the potential difference
- Use this data to work out the resistance for each measurement using potential difference divided by current
- Make sure the circuit doesn’t get too hot over the course of your experiment, as this will mess up your results. If the circuit starts to warm up, disconnect it for a while between readings so it can cool down.
- Repeat and calculate the means
Diodes
Only lets the current flow in one direction
