Topic 2 - electricity Flashcards
What is current and what is it measured in ?
Current is a flow of electrical charge.
It is measured in Amps (A)
What is potential difference and what is it measured in ?
The driving force that pushed charge around.
Measured in volts (V)
What is resistance and what is it measured in ?
Opposition to the flow of current/ slows it down.
Measured in ohms
What is the equation that links current , charge flow and time?
charge flow (coulombs , c ) = Current (A) x Time (s)
Q = IT
What is the equation that links potential difference, current and resistance?
Potential difference (V) = current(A) x resistance(ohms)
Describe how you can investigate the factors affecting resistance in a circuit (required practical )
1) set up equipment with ammeter in series and voltmeter in parallel to the crocodile clips.
2) Attach a crocodile clip to the wire, level with 0cm on the ruler.
3) attach the second clip to the wire 10cm away from the first clip and write down the length of the wire between the clips.
4) close the switch, then record the current through the wire and the pd across it using the ammeter and voltmeter.
5) open the switch then move the second crocodile clip another 10cm across the wire.
6) close the switch again and record the new length,current and pd.
7) repeat for a number of different lengths of the test wire.
8) use your measurements to calculate the resistance using r=v/i
9) plot a graph of resistance against wire length and draw a line of best fit.
Describe a method to find a components I-V characteristic. (required practical)
1) set up a test circuit with an ammeter a baterry and variable resistor and a component( ohmic conductor,diode,fliament lamp) in series and a voltmeter in parallel to the component.
2) Use the voltmeter and ammeter to record the potential difference and current .
3)vary the variable resistor to alter the current flowing through the circuit and the potential difference across the component.
4) Take several pairs of readings.
5)Swap the direction of the battery so the direction of pd is reversed
6) take several readings .
7) plot a graph of current against voltage for the component.
8) repeat with a different component.
What does an I-V graph for an ohmic conductor look like?
The current is directly proportional to the potential difference
What does an I-V graph for a filament lamp look like?
Straight in the middle, curved on the edges
as current increases so does the resistance
this means less current can flow per unit pd so the graph gets shallower.
What does an I-V graph for a diode look like ?
Current will only flow through a diode in one direction as it has very high resistance in the other.
What is an LDR and how does it work ?
give examples of devices that use LDR’s
Light dependant resistor
In bright light , the resistance falls
in darkness, the resistance is highest
e.g. automatic night lights
outdoor lighting
burglar detectors
What is a thermistor and how does it work ?
gice examples of where it can be used
A temperature dependant resistor
in hot conditions, the resistance drops
in cool conditions, the resistance goes up
higher temp provides more energy to electrons so they can move around more freely carrying charge
e.g. temp detectors
electronic thermostats
What are sensing circuits used for ?
Can be used to turn on or increase the power to components depending on the conditions they are in.
Describe all the features of a series circuit.
If one component is removed or disconnected the whole circuit is broken/stops.
The potential difference is shared across components.
The current remains the same across the whole circuit.
the total resistance across all of the components (the ‘net resistance’) increases as more components are added.
Describe all the features of parallel circuits.
If you remove one component it won’t affect the others.
Potential difference is the same across all components.
The current in a parallel circuitsplits into different branches then combines again before it goes back into the supply. When the current splits, the current in each branch after the split adds up to the same as the current just before the split.
In a parallel circuit,the net resistance decreases as more components are added, because there are more paths for the current to pass through.
If you have two resistor in parallel , their total resistance is _____ than the resistance of the s___________ of the two resistors.
If you have two resistor in parallel , their total resistance is less than the resistance of the smallest of the two resistors.
In a parallel circuit, each resistor provides an additional path for the current to
flow
This increases the total current in the circuit for the same potential difference,
which in turn lowers the total resistance
What is alternating current?
Current that constantly changes direction.
Produced by alternating voltages in which the positive and negative ends keep alternating.
What is direct current?
Current that always flows in one direction.
it is created by a direct voltage / potential difference
Is the uk mains supply alternating or direct current?
Alternating current
What is the frequency and volts of the uk mains supply?
50Hz
230V
What colour is the neutral wire in a plug and what does it do?
Blue
The neutral wire completes the circuit .
What colour is the live wire in a plug and what does it do?
Brown
Provides the alternating potential difference (230V) from the mains supply.
What colour is the earth wire and what does it do?
Green and yellow.
It is for protecting the wiring and for safety.
It stops the appliance casing from becoming live.
Why are live wires dangerous?
Your body is at 0 volts, so if you touch the live wire a large potential difference is produces across your body and a current flows through you causing an electric shock.
