P3.2: Simple Circuits Flashcards
Define current
The rate of flow of electric charge (or electrons) around a circuit
Current will only flow if there is a potential difference across that component and if the circuit is closed
Define potential difference
Driving force that pushes current around
Units: Volts
Define resistance
Measure of how easily a charge can flow
Unit: Ohms
What will the current be like in a single closed loop circuit?
Current will have the same value at any point
Charge formula
Charge (coloumbs) = current (amperes) x time (seconds)
How can you calculate energy transferred?
Charge x potential difference
What are the circuit symbols?
Page 45 CGP rev guide
What does the ammeter measure?
Current flowing through a component
Where must an ammeter be placed?
In line with component
Anywhere in main circuit
Never in the place of the voltmeter
What does a voltmeter measure?
Potential difference across the component
Where must a voltmeter be placed?
Parallel with the component under test
It can compare energy charge has beforee and after passing through component
How can you calculate potential difference?
Current x resistance
What do IV graphs show?
How current varies as you change pd
Why does resistance inc temp?
When electrons flow through a resistor, some of its energy is transferred to its thermal energy store
What happens when resistors heat up?
As resistor heats up, particles vibrate more. Particles jiggling makes it more difficult for electrons to pass through resistor
For most resistors there is a limit to current that can flow
More current means inc in temp. Inc in resistance - decrease in current
What is a diode?
A special device made from semiconductor material such as silicon
Current only flows in one direction through a diode and not the other
What is an LDR?
A resistor that’s dependent on light intensity
In darkness, resistance is highest
Light levels increase - resistance falls
Can be used in outside automatic night lights
What is a thermistor?
Used as temp detectors
Hot conditions - thermistor resistance drops
Cool conditions - thermistor resistance rises
What can sensing circuits do?
Used to turn on or increase the power to components depending on the conditions that they’re in
Which circuit devices can be used in sensing circuits?
LDRs
Thermistors
How are series circuits connected?
Connected in a line, end to end
Current has to flow through all components to get round the circuit
Removing a component can have a big effect
How are parallel circuits connected?
Each component is connected separately
Disconnecting one will hardly affect the others
What is PD like in series circuits?
Total pd of the supply is shared between the varioud components
Pds round a series circuit always add up to equal the pd across the power supply
V = V1 + V2
This is because total energy transferred to the charges in the circuit by the power supply equals the total energy transferred from charges to components
What is current like in series circuits?
Same currrnt flows through all parts of circuit
Size of current determined by total pd and total resistance
