What is electric charge?
A property of matter than can be a positive or negative charge and causes electric forces
What do, Conductors, Semiconductors, Insulators do?
Conductors - Many free electrons, carry current easily.
Semiconductors- Conductivity between conductor and insulator, can be changed.
Insulator- No free electrons, stop current
What is required for charge to flow?
A closed circuit and a source of Potential difference.
What is current?
Flow of electrons around a circuit or
Flow of electrical charge
Unit for charge, current and time?
Charge - Coloumb (C)
Current - Ampere (A)
Time - Seconds (s)
3 Mains electricity examples?
TV
Lights
Fridges
3 Battery- Powered examples .
Phones
Torches
Remotes
3 reasons why is sustainable power important?
Power stations wear out
Demand is growing
Need a mix that lasts
How does resistance affect current?
Inversely proportional relationship
Higher resistance - Smaller current
Lower resistance - Larger current
Current in a series circuit ?
Same everywhere
Potential difference in a series circuit?
Sum of all components
Current in a parallel circuit?
Splits between branches (adds up to total)
Potential in a parallel circuit?
Same across each branch
How does adding a resistor in a parallel affect total resistance?
Total resistance DECREASES, it’s always less the the smallest resistor.
In ‘Investigation factors affecting resistance’ why keep the wire constant?
To avoid temperature affecting resistance. Ensures only length is tested.
In ‘Investigation factors affecting resistance’
what could be the source of error when measuring resistance on a wire?
Heating of wire by current by current changes resistance.
Reduce this error by using low current/switching between reading
Why does increasing wire length increase resistance?
Electrons travel further
More collisions with metal ions
More energy lost
What is meant by ohmic conductor?
A conductor whose resistance remains constant as the current changes.
Provided the temperature is constant
What is the relationship between current and potential difference in an ohmic conductor?
Current is directly proportional to potential difference. (V ∝ I).
Give an example of an ohmic conductor.
A fixed resistor (at constant temperature)
4 components where resistance isn’t constant
Filament lamp
Diodes
Thermistors
Light dependant Resistors
Why does a filament lamp’s resistance increase as it’s used?
As current flows, the filament’s temperature rises, causing increased resistance.
Describe the current-Voltage behaviour of a diode
Current flows easily in one direction, when reversed, resistance is extremely high and current is basically none
What happens to resistance of a thermistor as temperature increases?
Resistance decreases = temperature increases
