P2 Book work Flashcards
(23 cards)
Definition for resistance
The ability for an electrical components to resist the flow of current and measured in ohms
Describe a circuit resistance (length of a wire) practical
-set up circuit with a power supply, ammeter, the test wire and volt meter in it
-Set the variable power supply to 6V
-Make sure one crocodile clip is it one end of the wire being tested
-Clip the second crocodile clip to the wire 20 cm away from the other end
-Switch on power supply and record readings from the ammeter and voltmeter
-Switch off power supply and move the clip further along the wire and record readings
-repeat for different lengths of the wire
What is an ohmic conductor?
-Directly proportional relationship between potential difference and current
-Components that are ohmic conductors have a constant resistance
-examples are resistor, thermistor, LDR
What is a filament bulb?
-non-linear relationship
-Curve Plateaus as current increases
-This is because resistance is increasing
-Resistance increased due to rise in temperature of the wire
What is a diode?
-non-linear relationship
-Diode has a lower resistance in the direction but high resistance in the reverse
-High resistance causes flat line on left of IV characteristic
Describe a method for an IV characteristic experiment
-Set up circuit including ammeter, voltmeter, fixed/variable resistor and a voltage supply
-Switch on the ammeter and volt meter to ensure they show positive readings and if not switch their connecting wires around
-Adjust power supply or variable resistor and record new current and potential difference
-Switch off the circuit and swap the wires attached to the component you are testing so both the ammeter volt meter show negative readings
-repeat the steps and then replace the resistor with a diode and then with a filament bulb
Describe a method to show how the current in a filament lamp varies with the potential difference across the filament lamp
-Set up circuit
-Set potential difference to lowest value
-Measure current and potential difference using ammeter voltmeter
-repeat for different values of potential difference
-Increase potential difference by 2V each time until 6V
-Reverse the connections and collect negative values
-Plot a graph of current against potential difference
-Take repeats and calculate the mean
Define thermistor
Relationship between temperature and resistance is inversely proportional. as temperature increases, resistance decreases
Define LDR
Relationship between light intensity and resistance is inversely proportional. As light intensity increases resistance decreases.
Definition for AC and DC
AC- alternating current is when current flows in different directions
DC-direct current is when current flows in one direction
Diode, current, potential difference, resistance definition
diode- a component that only flows in a forward direction
Current- the flow of electrons
Potential difference- energy carried by the electrons in a circuit
Resistance- a measure of the opposition to flow in an electrical current and measured in ohms
Parallel and series definitions
Parallel- components connected in parallel have the same potential difference and current is equal to the sum of the components
Series - components connected in series have the same current but share potential difference
Step up/down transformer definitions
Step up – device that increases the potential difference along cables
Step down – device that low is the potential difference before it reaches the consumer to make it safe
What is the earth wire for?
If a fault occurs and the live wire becomes loose a person to use the appliance could get electrocuted so the earth wire provides a low resistance path to the ground so current passing through will follow the path to the ground instead of the person
What does a fuse in a plug do?
Provides a built-in failsafe that melts if current gets too high and once melted the circuit is broken so current can’t flow through the device and is no longer live so there is no more risk of electrocution 
What does outer insulation in a plug do?
All three wires in the cable are bundled together and there is extra plastic insulation wrapped round them all for safety
What is the cable grip for in a plug?
Holds the cable tightly in place so the wires don’t become loose
What is the live wire in a plug?
Copper wire coated with brown plastic along which the current enters the device
What is the neutral wire?
Copper wire coated with blue plastic that’s also connect to the cable in the wall and complete the circuit
Mains electricity is a supply of alternating current that has a frequency of ? And potential difference of ?
Frequency – 50 Hz
Potential difference – 230 V
What happens in a power station?
Store of chemical energy converted into electricity, fuels are burnt and converted to steam with heat, under pressure electric generator, current produced is called alternating current, chemical energy is usually in the form of fossil fuels
What happens in transmission cables?
Facilitates movement of high voltage power supplies, electricity passes through transmission lines at high potential difference and low current, creates high resistance so is more efficient and thinner wires can be used, wires are held up by pylons
Where are step up/step down transformers found?
Step up – after the power plant, before pylons
Step down – after pylons, before consumers
