Electricity Flashcards
What causes current to flow?
For a current to flow in a closed circuit, there must be a source of potential difference.
What is an electric current?
A flow of electrical charge. The size of current is the rate of flow of electrical charge.
What is the value of current in a closed loop?
Current has the same value at any point in a single closed loop.
How is current related to potential difference for an Ohmic conductor?
Current is directly proportional to potential difference across the resistor
What happens to resistance in an Ohmic conductor when the current across it changes?
It stays constant
What happens to resistance of filament lamp as temperature changes?
Resistance increases as temperature increases. Not directly proportional. Non-linear
What does a diode do?
Current flows only one way through a diode. Diode has very high resistance in the opposite direction.
How does the resistance of a thermistor change?
Resistance decreases as temperature increases
How does resistance of LDR change?
Resistance of an LDR decreases as light intensity increases.
What are the rules for current in a series circuit?
Same across each component
What are the rules for potential difference in a series circuit?
Supply power is shared between components
What are the rules for resistance in a series circuit?
Total resistance is the sum of resistance in each component.
What are the rules for current in a parallel circuit?
Total current is the sum of the current through each branch.
What are the rules for potential difference in a parallel circuit?
Potential difference across each component is the same as the supply.
What are the rules for resistance in a parallel circuit?
Total resistance of the resistors is less than the resistance of the smallest individual resistor.
What is AC?
Alternating current switches direction periodically
What is DC?
Direct current travels continuously in the same direction
What is the magnitude and frequency of the UK mains supply?
UK mains potential difference is 230 V and the AC frequency is 50 Hz
What colour is the neutral wire?
blue - carries electricity out at 0 V
What colour is the Earth wire?
yellow and green - stops appliance from becoming charge
What colour is the live wire?
brown - this provides the alternating potential difference - electricity flows in
Why is the Earth pin the longest on a UK plug?
It makes contact first so that the circuit is grounded before connecting the main part of the circuit.
How do materials become electrically charged?
When insulating materials are rubbed against each other (applying friction) they become electrically charged. Negatively charged electrons are rubbed off one material and on to the other. The material that gains electrons becomes negatively charged. The material that loses electrons is left with an equal positive charge.
