Electricity Flashcards
Electrical circuits explained
Energy is supplied to electrons by a cell/battery or mains electricity. Which then move through the wires to transfer energy. Cells/ batteries have a store of chemical energy.
What is current
The rate of the flow of charge
How do electrons move in a circuit
The charge travels from the cell/battery to the lamp where all of their energy is converted into light
What is potential difference
The measure of how much is energy is transferred to each coulomb of electrons/charge. Unit:volt(V)
Where are voltmeters connected
Parallel to components
Potential difference equation ET=C
Potential difference = energy transferred(J) / charge(c)
Where are ammeter always components
In series with components
Resistance meaning
The measure of how much a component/object resists the flow of current. Unit ohms
Potential difference equations
Potential difference = current(A) x resistance(ohms)
Fixed resistor explained
Straight line t1hrough origin. V and I are (directly proportional, constant gradient = constant R
Filament lamp explained
Line curves, resistance not constant. This is due to delocalised electrons colliding with ionic lattice which causes them to vibrate more. A larger current results in an increased resistance(non-ohmic)
Led-diode explained
Diodes only let current flow in one direction:low resistance in forward directions. High resistance in reverse directions
Series circuit features
Total P.D is shared between all components
Current is the same for all components
Total resistance = sum of resistances
Parallel circuit features
P.D for each branch=P.d of cell/battery
Current is split between the branches
Adding more resistors in parallel reduces total resistance
Thermistor explained
Does the opposite to a metal/filament. If temperatures increases, resistance decreases.
LDR explained
Similar to a thermistor but for light: if light intensity increases, resistance decreases.
What is direct p.d
A p.d that only acts in one direction(results in D.C(direct current) e.g. from a battery
Describe Neutral wire
Blue wire. Stays at 0v
Live wire
Changes between positive and negative potentials which average out a 230 V this is UK mains voltage.
Brown wire
Earth wire
Safety feature it acts as an escape route for a current that would otherwise cause a shock if the appliance is touched. Not needed for double insulated appliance
What type of current is main electricity
Alternating current. Resulting from an alternating P.D. (Both of these reverse direction at frequency of 50HZ, at least in the UK)
National grid definition
Distributes electricity to where its needed
Power station
Produce a relatively high current. If this went straight into the grid, a huge amount of energy/power would be lost as heat due to the resistance of cables.
Step up transformer
Increases the transmission voltage to 132KV(132,000V) which decreases the current, less power lost due to heating in the cables.
What is static electricity
Transferred between insulating materials, they will remain charged - this is static electricity
What is the magnetic law
Opposite charges attract and like charges repel
Electron law explained
Electrons are negatively charged so if an object gains electrons, it becomes negatively charged if it loses them it becomes positively charged.
Writer the equation that links current, potential difference and power
Current = power/potential difference
What is potential difference
P.D is the measure of how much energy is transferred to/by each coulomb of electrons/charge
How are voltmeters connected
Always connected in parallel
What is current
The rate of flow of charge
How are ammeters connected
Always connected in series with component
What is resistance
The measure of how much a component/object resists the flow of charge unit ohms
What relationship do current and potential have
Directly proportional
Describe fixed resistor graph
Straight line through origin : potential difference and current are directly proportional. Constant gradient = constant resistance. It is ohmic. If another resistor gives a steeper gradient, it must have a lower resistance
Describe filament lamp graph
Line curves : resistance is not constant. This is due to delocalised electrons colliding either ionic lattice, which causes them to vibrate more, and temperature increase. A large current results in an increased resistance (Non ohmic)
Describe diode graph
Diodes only let current flow in one direction: low resistance in forward direction. High resistance in reverse direction
Describe series circuits
Total potential difference is shared between all components.
Current is the same for all components.
Total resistance = sum of resistances
If resistors are identical, total V must be shared equally. If not, the bigger resistance takes a bigger share of voltage.
Describe parallel circuits
Potential difference for each branch = potential difference of cell/battery
Current is split between the branches
Adding more resistors in parallel reduces the total resistances
Describe a thermistor
Does the opposite to a metal/filament : if temperature increases, resistance decreases.
Describe an LDR(light dependent resistor)
Similar to a thermistor, but for light: if light intensity increases, resistances does
What’s is direct potential difference
Potential difference that only acts in one direction. This results in direct current(D.C) e.g. from a battery
Describe mains electricity in terms of current and potential differences
Alternating current resulting from an alternating potential difference
What voltage is the neutral wire
Stays at 0 volts
What voltage is the live wire
Changes positive + negative potentials, which average out at a P.D of 230V - this is the u.k mains voltage
Describe the earth wire
Safety feature : it acts as an escape froute for current that would otherwise cause a shock if the appliance is touched. Not needed for double insulated appliances.
What colour wire is the neutral earth and live
Live wire - brown
Neural wire - blue
Earth wire - yellow and green
What do power stations do in the national grid
Produce a relatively high current. If this went straight into the grid, a huge amount of energy/power would be lost and heat due to the resistance of the cables
What does a step up transformer do in the national grid
Increases the voltage(132Kv), which decreases the current, reducing the power lost due to heating in the cables.
What does a step down transformer do
Reduces the voltage down to a safer and usable 230V for homes and businesses
