Section 2 - Electricity P1 (also have physical circuit flashcards)
Define current:
Current is the rate of flow of charge round the circuit
What is the unit for current?
ampere (amp)
A
What carries the charge in a circuit?
Electrons usually carry the charge
Define voltage:
Voltage is what drives the current round the circuit.
What is another word for voltage?
Potential difference
What is the unit for volts?
volt
V
Define resistance:
Resistance is anything in the circuit which slows the flow down
What do components do to the resistance of a circuit?
The more components in a circuit the higher overall resistance there will be
What does current need to flow?
Current will only flow through a circuit if there is a voltage across it
What is the unit for resistance?
ohm
Ω
What is the relationship between current and voltage?
If you increase the voltage, then more current will flow
What is the relationship between current and resistance?
If you increase the resistance, then less current will flow
What is an ammeter? And where is it put in a circuit?
Ammeter measures current flowing through a component
Must be placed in series
What is an voltmeter? And where is it put in a circuit?
Voltmeter measures the voltage flowing through a component
Must be placed in parallel around a component, not around a variable resistor or battery
How would you set up apparatus for current-voltage graphs?
- make a circuit with a component, ammeter and the variable resistor are all in series, with the voltmeter in parallel over the test component
- as you vary the variable resistor. it varies the current
- this allows you to take several pairs of readings
- plot these values on a current(y)-voltage(x) graph
What is AC electricity supply? And what does AC mean?
AC (alternating current), is used for mains supply
AC - means the current is constantly changing direction
What is DC electricity supply? And what does DC mean?
DC (direct current) is used for battery supply
DC - means the current keeps flowing in the same directon
What is the UK mains electric supply in volts?
AC - 230 volts
What is the equation linking Current, Voltage and Resistance?
Voltage = Current x Resistance
Describe a graph of current against voltage for a circuit with a wire in:
The current through a wire (at a constant temperature) is proportional to voltage.
Describe a graph of current against voltage for a circuit with different resistors in:
The current through a resistor (at a constant temperature) is proportional to the voltage.
Different resistors have different resistances, hence they have different gradients of proportionality.
Describe a graph of current against voltage for a circuit with a metal filament lamp in:
As the temperature of the metal filament increases, the resistance increases (hence the elongated f shape)
Describe a graph of current against voltage for a circuit with a diode in:
Current will only flow through a diode in one direction.
So the graph will only increase in one quadrant
What does LED stand for?
Light-emitting diodes
What do Light-emitting diodes do?
They emit light when a current flows through them in the right direction
What are the practical applications of LEDs?
- digital clocks
- traffic lights
- remote controls
What is the difference between an LED and a light bulb?
LEDs don’t have a filament that can burn out, light bulbs do
What is the general purpose of LEDs or light bulbs in a circuit?
They indicate the presence of of current in a circuit.
What is a LDR?
Light Dependent Resistor
-a resistor which changes its resistance depending on how much light falls on it
In bright light what is the resistance like in a LDR?
- the resistance is highest in bright light
- the resistance is lowest in darkness
What are the uses of a Light Dependent Resistor?
Useful device for various electronic circuits
Burglar Detectors
What is a thermistor?
a thermistor is a temperature dependant resistor
In hot conditions what is the resistance like in a thermistor?
- the resistance drops in hot conditions
- the resistance rises in cold conditions
What are the uses of a thermistor?
Make useful temperature detectors
- car engine temperature sensors
- thermostats
- fire alarms
What is an example of a series circuit?
in use in life
Fairy lights
What is a series circuit?
When all components are connected in one single loop between the +ve and -ve of the power supply (except for voltmeters)
-if you remove one component the whole circuit will stop working
In a series circuit, what happens to the potential difference when you add more cells?
What are the rules about potential difference in a series circuit?
The potential difference (voltage) increases when you add more cells to a series circuit
- potential difference is shared between all components
- potential difference for each component depends on its resistance
In a series circuit, what are the rules about current?
- current is the same everywhere
- the size of the current depends on the total potential difference and the total resistance of the circuit (I=V÷R)
In the series circuit, what are the rules about resistance?
- the total resistance depends on the number and type of components present in the circuit
- total resistance = the sum of the resistance of each component in the circuit
What is a parallel circuit?
When each component is separately connected to the +ve and -ve of the power supply
-if you remove 1 component it will hardly effect the rest
What is an example of a parallel circuit?
in use in life
- most things connected in cars
- household electrics
- light switches in your house, each are on branches of a parallel circuit
Are common everyday circuits parallel or series?
Normally contain a mixture of series and parallel parts
In a parallel circuit, what are the rules for potential difference?
The potential difference is the same across all the branches
In a parallel circuit, what are the rules for current?
- current is shared between the branches
- total current = total of all the currents through separate components
- in parallel circuit junctions, the total current in = the total current out
- the current through a branch depends on the resistance of the branch (higher resistance = lower current)
In a parallel circuit, what are the rules for resistance?
-the total resistance of a circuit decreases if you add a second resistor in parallel
What is the equation linking current, charge and time?
Q = I x t
Q - charge [unit = C (coulomb)]
I - current [unit = A]
t - time [unit = seconds]
What is the relationship between charge and voltage?
The bigger the change in voltage, the more energy is transferred for a given amount of charge passing through the circuit.
-a battery with a bigger voltage will supply more energy per coulomb of charge which flows round
VOLTAGE IS THE ENERGY TRANSFERRED PER UNIT CHARGE PASSED
One volt =
one joule per coulomb
What is the equation linking voltage, energy transferred and charge?
energy transferred = charge x voltage
What is the equation linking resistance, energy transferred, charge and current?
energy transferred = charge x current x resistance
What are the three wires in a plug?
live
neutral
earth
What wires are needed in a plug?
The live and neutral wires
-if something goes wrong,the earth wire there for safety
What is the colour and features of the live wire?
colour: brown
- alternates between a high +ve and -ve voltage of about 230V
- electricity normally flows in through this wire
What is the colour and features of the neutral wire?
colour: blue
- is always at 0V
- electricity normally flows out through the neutral wire
What is the colour and features of the earth wire?
colour: green & yellow
- works with fuse or a circuit breaker for safety
What is the safety precaution for appliances with a metal casing?
- being ‘earthed’,to reduced the danger of electric shock
- the case must be attached to an earth wire, an earthed conductor can never become live
What is the name for an appliance with a plastic casing? And why do appliances with plastic casings not need extra precautions?
double insulated
-plastic is an insulator so you can’t get a shock so an earth wire isn’t needed
What does an earth wire and fuse or circuit breaker do if a fault develops in which the live wire touches a metal casing?
- the case is earthed
- a big current flows in through the live wire, through the case and out down the earth wire
- the surge in current melts the fuse (or trips the circuit breaker), which cuts of the live supply
What does the fuse melting or the circuit breaker tripping do?
- it isolates the whole appliance, making it impossible to get an electric shock from the case
- prevents the risk of fire by the heating effect of a large current
What are circuit breakers?
An electrical safety device used in some circuits
-they protect the circuit from damage if too much current flows (like fuses)
How do circuit breakers work?
- they detect a surge in current of a circuit
- they break the circuit by opening a switch
- they can be reset by flicking a switch on the device
What is the advantage of a circuit breaker over a fuse?
CIRCUIT BREAKER MORE CONVENIENT THAN FUSE
-circuit breakers need a switch flicked to reset them
-fuse needs to be replaced once it has melted
OPERATE MUCH FASTER THAN FUSES (SAFETY)
-circuit breakers break the circuit straight away
-fuse waste time, waiting to melt
RCCBs ARE BETTER @ PREVENTING ELECTROCUTION
-RCCBs work for small current changes
-the current might not be enough to melt a fuse
What is a common type of circuit breaker?
Residual Current Circuit Breaker (RCCB)
What does a RCCB do?
Normally the same current flows through live & neutral
- if someone touches the live then this means the current will flow through them to earth, so the neutral wire carries less current than the live
- RCCBs detect this difference in power and cuts of the power by opening a switch
When there is an electric current in a resistor, what energy transfer is there?
And why does this occur?
an energy transfer which heats the resistor
-because the electrons collide with the ions in the lattice that makes up the resistor, this gives the ions energy which causes them to vibrate and heat up
What can the heating effect of a resistor do?
Cause components in a circuit to break
- causing circuits stop working or not work properly
- fuses use this effect to melt and break the circuit
What are the uses of a resistor?
- for fuses to melt
- toaster (contain coils of high resistance wire, as the temperature increases it gives of infrared radiation)
What is electrical power?
The rate at which an appliance transfers energy.
power (watts) = joules per second
What is the equation linking electrical power, voltage and current?
P = I x V
P - Electrical power [unit = watts(W)]
I - Current
V - Voltage
What is the equation linking current, time. energy transferred and voltage?
Energy transferred = current x voltage x time
