P2 - Electricity Flashcards
What is electric current and what is the equation that links charge, current and time?
An electric current is a flow of charge
Charge = current × time
Q = I × t
What is potential difference and what is the equation that links potential difference, energy transferred and charge?
Potential difference is the energy that the charge carriers gain or lose as they go through components.
Energy = potential difference × charge
E = V × Q
What is Ohm’s law and what is the equation that links potential difference, current and resistance?
Ohm’s law states that
“The current through a resistor (at a constant temperature) is directly proportional to the potential difference across the resistor.”
Potential difference = current × resistance
V = I ×R
What does a diode do?
A diode only let’s current flow in one direction
Current can only flow in the direction that the triangle points in.
How does temperature affect the resistance of a thermistor?
As the temperature increases the resistance of a thermistor decreases
Which components give these 3 IV characteristic graphs?
(x-axis is potential difference, y-axis is current) :
1 - Straight line
2 - Curvy then straight then curvy
3 - Straight then curve up
1 - Resistor
2 - Filament lamp
3 - Diode
How do you find the total resistance of 2 or more components in a series circuit?
Add up the resistance of the individual components
What happens to the resistance when a parallel branch is added to a circuit?
The resistance decreases.
It is ALWAYS less than the smallest resistor
How do you work out the current and potential difference in a series circuit?
The current is the same at all points.
The potential difference is shared between the components.
How do you work out the current and potential difference in a parallel circuit?
The current is split between the branches/loops
The potential difference is the same across every branch/loop
What is the difference between direct and alternating current?
Alternating currents repeatedly reverse their direction.
Direct currents flow in one direction all the time
What is the potential difference and frequency of mains electricity?
Mains electricity has a potential difference of 230 V and a frequency od 50 Hz
What does a step up transformer do?
A step up transformer increases the size of the potential difference
What are the 3 wires in a plug called and what does a fuse do?
1 - Brown wire is the live wire
2 - Blue wire is the neutral wire
3 - Yellow and green wire is the Earth wire
A fuse melts when the current gets too big and breaks the current
What is the job of the Earth wire
It is a safety feature.
It is connected to the metal vase of appliances and carries current only if there is a fault
What is the potential difference between the live wire and the earth wire?
230 V
What is the potential difference between the neutral wire and the earth wire?
0 Volts
What are the 2 equations for electrical power?
Power = current × potential difference
Or
Power = energy transferred ÷ time
What is the network of pylons and transformers that carry electricity around the country called?
The National Grid
Describe how the national grid uses transformers to make energy transfer more efficient?
It transfers electricity at high voltage.
- This means less current is needed
- This means that the wires don’t heat up as much
