P4 - Electricity✔️ Flashcards
Define electric current?
Flow of electrical charge which will only flow round a complete circuit if there is a potential difference - unit of current is ampere, A
What is potential difference?
Potential difference or voltage is the driving force that pushes the charge round - units is the volt, V
What is resistance?
Resistance is anything that slows the flow down - unit is ohm , Ω
What does current flowing through a component depend on?
- potential difference across it
- resistance of the component
What are ohmic conductors?
Components where the resistance does not change with current (eg wire or a resistor) - at a constant temperature, the current flowing through an ohmic conductor is directly proportional to the pd across it
Give two examples where the resistance of some resistors and components change?
- diode
- filament lamp
For diodes what does the resistance depend on?
Resistance depends on the direction of the current - will let current flow in one direction, but have a very high resistance if its reversed
Explain what happens when electrical charge flows through a filament lamp?
Transfers some energy to the thermal energy store of the filament, which is designed to heat up - resistance increases with temperature so as current increases (the lamp heats up more) which further increases resistance
What does ‘I-V characteristic’ refer to?
Refers to a graph which shows how the current flowing through a component changes as the potential difference acrosss it is increased
I-V characteristic of linear components (eg fixed resistor)?
Straight line I-V characteristic
I-V characteristic of non-linear components (eg filament lamp, diode)?
Curved I-V characteristic
What does LDR stand for?what are there uses?
Light dependent resistor - is dependent on the intensity of light - used for automatic night lights and outdoor lighting
Explain the effects of changes in light on resistance of an LDR?
- bright light, the resistance falls
- darkness, the resistance is highest
What is a thermistor?what are there uses?
A temperature dependent resistor - which can be useful temperature detectors, eg car engine tempeature sensors
Explain the effects of changes in temperature on resistance of a thermistor?
- hot conditions, the resistance drops
- cool conditions, the resistance goes up
What is a series circuit?
- Circuit where the different components are connected in a line (end to end) - if you remove or disconnect one component, the circuit is broken and they all stop
- not very handy - very few things are connected in series
Relationship between pd in a series circuit?
The total pd of the supply is shared between the various components
Relationship between current in a series circuit?
The same current flows through all components - size of the current is determined by the total pd of the cells divided by total resistance of the circuit
Relationship between resistance in a series circuit?
You can work out the total resistance of all the components by adding up there resistances together
What is a parallel circuit?
- Each component is separately connected to the +ve and -ve of the supply - if you disconnect a component it wont effect the others
- most things connected like this, for example cars and household electrics
Relationship between pd in a parrallel circuit?
Pd is the same across all components - because all components get the full source pd which means that all identical bulbs connected in parallel will be at the same brightness
Relationship between current in a parallel circuit?
Total current flowing around the circuit is equal to the total of all the currents through the seperate components - you can work out the total current by adding the current flowing through each component
Relationship between resistance in parallel circuits?
If you have two resistors in parallel, their total resistance is less than the resistance of the smallest of the two resistors
How is static caused by friction?
When certain insulating materials are rubbed together, negativley charged electrons will be scraped off and dumped on the other - leaves the materials electrically charged (one negativley and the other positivley)
What dertermines the direction the electrons are transferred when static is built up?
- depends on the two materials involved
How can too much static cause a spark?
If the pd gets large enough, electrons can jump across the gap between the charge object and earth - this is the spark
explain what causes a static shock?
When the electrons jump to any earthed conductor that is nearby - result of the pd getting too large
Define electrostatic attraction?
Non contact force that is a result of oppositely charged electric charges repeling or attracting each other
Explain what an electric field is?
Field created around any electrically charged object - the close you get to the object the stronger the field is
What happens when a charged object is placed in an electric field?
It feels a force - causes attraction or repulsion as a result of the electric field of each charged object interacting with each other
How is a spark caused explain with refrence to electric fields?
Cuased when there is a high enough pd between charged object and the earth - causes a strong electrical field - which causes electrons in the air particles to be ionised - makes air more conductive, so current flows through it - this is the spark
