Electricity and Circuits Flashcards
What three subatomic components make up an atom?
Electrons, protons and neutrons
What is the structure of an atom?
Neutrons and protons in the nucleus and electrons surrounding the nucleus in shells
What are the names of charged particles in the atom?
Proton (+1) and Electrons (-1)
What is current?
As the rate of flow of charge around a circuit
What are the units of charge?
Coulombs
What factors affect the energy transferred when charge flows through a component?
Amount of charge and potential difference across the component
What is the equation of energy?
energy = p.d x current x time
What is potential difference?
The work done per unit charge
What is the equation of potential difference?
energy transferred = charge x p.d
When an electrical current flows through a resistor why does it heat up?
There are collisions between the electrons and ions in the resistors lattice, this causes a transfer of KE into thermal energy which is released into the surroundings
How do low resistance wires reduce unwanted energy transfers?
A smaller resistance will mean there are fewer collisions, therefore less energy will be wasted through heating
What are some advantages of the heating effect?
It’s useful for appliance where the heat is the desired product
What are some disadvantages of the heating effect?
The loss of energy as heat energy can make an appliance inefficient and if an appliance overheats nit can catch fire or overheat which could ruin the device or injure the user
What is the equation of power?
Power = current x p.d
Power = current^2 x resistance
Power = energy / time
Power = p.d^2 x resistance
What does AC mean?
Alternating current, constantly changing between a negative and positive maximum
What does DC mean?
Direct current, takes a constant value
Is maims electricity an AC supply or a DC supply?
AC supply
What is meant by the frequency of a supply?
The rate at which an AC current changes
What is the frequency and voltage of the UK mains electricity supply?
Frequency: 50Hz and Voltage: 230V
What type of current do batteries and cells supply?
Direct current
What is the power rating of an appliance?
It shows how much energy a device converts per seconds
What wires does a typical domestic appliance have?
Live, neutral and Earth wire
What colour is the live wire?
Brown
What colour is the neutral wire?
Blue
What colour is the earth wire?
Green and yellow (striped)
When does and doesn’t the Earth wire carry a current?
Under normal circumstances no current flows and current flows when a fault occurs in the appliance
What potential is the neutral wire at?
0 volts
What is the potential difference between the live and earth wires?
230 volts
What is the purpose of the neutral wire?
To complete the circuit by connecting the appliance back to the Maine supply
For metal appliances, where is the Earth wire connected to?
Metal casing of the appliance because if live wire becomes touches the casing, the current will flow through the Earth wire, preventing electrocution
How does fuel stop a device from getting damaged?
When the current becomes too high the fuse wire will melt and break, therefore stopping current flowing to the appliance and preventing damaging
Why is it I pot connect a fuse or switch to the live wire?
When the switch is turned off, or when the fuse breaks, it will break the circuit and stop current running through the wire and this provides a method to stop current flowing into the appliance
Why is it dangerous to have a connection between the Earth wire and live wire?
In can result in a current surge, causing electrical shocks
How does resistance affect current in a circuit?
As the total resistant of a circuit increases, the current flowing through the circuit decreases
How can the current in a circuit be varied?
Using a variable resistor
What is the equation of p.d?
p.d = current x resistance
How is total resistance affected by two resistors in series?
The total resistance increases, it’s equal to the sum of the two resistors
How is total resistance affected by two resistors in parallel?
The total resistance decreases, it’s less than the resistance of the resistor with the lowest resistance
What is an ‘Ohmic Conductor’?
A conductor for which current and potential difference are directly proportional, resistance remains constant as current change and temperature must be constant
What are some components for which resistance is not constant as current changes?
Filament lamps, diodes, thermistors and light dependent resistors
What happens to the resistance of a filament lamp as the temperature increases?
Resistance increases, metal ions have more KE so vibrate more colliding more frequently with electrons as they flow through the metal and this creates more resistance to current flow
What is different about current flow through a diode?
The current only flows in one direction and resistance is very high in the other direction preventing current flow
What happens to the resistance of a thermistor as temperature increases?
The thermistors resistance decreases
What are two examples of when a thermistor may be used?
In a thermostat to turn a heater on below a certain temperature and in a freezer to turn on a collar when the temperature becomes too high
What happens to the resistance of a LDR as light intensity decreases?
The LDR’s resistance increases
What is an application for a LDR?
Street lamps or night lights, when light levels drop resistance increases and the light gains sufficient current to turn on
How do diodes work?
A diode only allows current to flow in one direction, if current is flowing the right way, the resistance is large for small voltages but then at higher voltages becomes very small
