P2 - Electricty - Revision - GCSE Flashcards
Keywords
Define voltage
Energy per charge
Keywords
Define current
The rate of flow of charge
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Define plug
Connects appliances to the mains
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Define earth wire
Safety wire that prevents an appliance becoming live by redirecting excess current to the ground
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Define neutral wire
Completes the circuit
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Define live wire
Carries electricity from the mains to the appliance
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Define static electricity
Charge that accumulates on an insulated object due to things such as friction
Keywords - circuit components
Bulb
Lights up when current passes through
Keywords - circuit components
Voltmeter
Measures potential difference (in volts)
Keywords - circuit components
Ammeter
Measures current (in amps)
Keywords - circuit components
Cell/battery
Provides a potential difference in a circuit
Keywords - circuit components
Switch
Turns circuit on and off by breaking or completing it
Keywords - circuit components
Resistor
Provides resistance - making it more difficult for current to flow
Keywords - circuit components
Variable resistor
Provides a changeable resistance
Keywords - circuit components
Fuse
Heats up and melts, breaking the circuit, when current is too high
Keywords - circuit components
Diode
Keeps current flowing in one direction
Keywords - circuit components
Thermistor
Changes resistance based on temperature, decreasing resistance when temperature increases
Keywords - circuit components
Light dependent resistor
Changes resistance based on light, resistance decreases when light intensity increases
Keywords - circuit components
Have you revised circuit symbols?
Yes
Circuits - properties
What is the equation for current, charge and time? (Hint: derive it from the definition of current)
Give units as well
I = Q / t
I - Amps
Q - Coulombs (C)
t - time (s)
Circuits - properties
What does charge do?
Carries energy from the battery to circuit components
Circuits - properties
What is the bread - bakery model of circuits?
Bread goes from bakery to shop on vans and roads in the same way charge travels round a circuit to components
Circuits - properties
Define a parallel circuit
A circuit in which there is more than one pathway for current to flow
Circuits - properties
Define series circuit
A circuit where there is one pathway for current to flow
Circuits - properties
What happens to current in a series circuit?
Stays equal throughout
Circuits - properties
What happens to current in a parallel circuit?
It splits across branches
Circuits - properties
What happens to potential difference in a series circuit?
It splits across components
Circuits - properties
What happens to potential difference across a parallel circuit
It stays equal on each branch
Circuits - properties
What is the total resistance in a series circuit?
Sum of each resistors’ resistances
Circuits - properties
What is the sum of resistance in a parallel circuit?
Less than the resistance of the smallest resistor
Circuits - properties
Give the equation for voltage (hint: it is derivable from the definition of voltage)
And give units
V = E/Q
V - volts - V
E - Energy - Joules - J
Q - Charge - Coulombs - C
Circuits - properties
What is ohms law (equation and explanations)
Give units as well
V = I R
V - volts - V
I - Current - Amps - A
R - resistance - Ohms - Ω
Voltage is directly proportional to current with constant current (and proportional to resistance with constant current)
Resistance is inversely proportional to current
Circuits - properties
Give the 2x equations for power and the equation you use to derive it
Give units as well
P = I V
P = E / t
P - Watts - W
I - Current - Amps - A
V - Voltage - Volts - V
P = I squared x Resistance
I - current - Amps
Resistance - Ohms - Ω
Required practicals - resistance and length of wire
What are the independent, control and dependent variables in the investigation?
Independent - length of wire
Dependent - resistance
Control - current, voltage, wire temperate and thickness
Required practicals - resistance and length of wire
Write the method for this investigation
Fix crocodile clips to bare wire 10 cm apart
Get ammeter and voltmeter readings (to find initial resistance)
Disconnect the circuit and increase the distance between the crocodile clips by 10cm - wait 10 secs
Connect and get ammeter and voltmeter readings
Repeat until 100cm
Draw a graph of voltage and current (voltage on y axis as resistance should be the gradient)
Required practicals - resistance and length of wire
What should the conclusion of the investigation be?
Resistance and length of wire are directly proportional (as length of wire increases so does resistance)
Required practicals - ohms law on a resistor
What components do you need to set up this circuit?
Resistor, variable resistor, voltmeter attached in parallel on the resistor, battery, switch
Required practicals - resistance and length of wire
True or false: you should connect the voltmeter in parallel measuring the potential difference of the bare wire in the investigation
True
Required practicals - ohms law on a resistor
Write a method for this investigation
- Set variable resistor on lowest resistance
- Record voltage and ammeter readings
- Increase resistance incrementally (1 Ω segments)
- Repeat at least 6 times
Plot the graph
Required practicals - ohms law on a resistor
What should the conclusion of this investigation be?
That ohms law applies on a resistor (it is an ohmic conductor)
Required practicals - resistance in series vs parallel circuits
What components to you need in this circuit
Resistance x 2, voltmeter, ammeter, switch, battery
Required practicals - resistance in series vs parallel circuits
What is the independent, control, dependent variable in the investigation
Independent - arrangement of the resistors
Control - resistor, battery, voltage, length of wire
Dependent - total resistance in the circuit
Required practicals - resistance in series vs parallel circuits
Write the method for the investigation
- Take a reading of current and voltage in a series arrangement
- Take the same readings in a parallel arrangement
- Compare results
Required practicals - resistance in series vs parallel circuits
What should the conclusion be for the investigation?
Resistance is higher in a series circuit (sum of resistance of resistors) than parallel (less than the lowest resistor)
Required practicals - Ohms law in different components
Does a bulb follow ohms law - draw the graph of a filament bulb and plot voltage and current
No
Required practicals - Ohms law in different components
Why doesn’t a bulb follow ohms law
It heats up and this increases resistance through the movement of positive metal ions preventing the movement of electrons throughout the circuit
Required practicals - Ohms law in different components
Does a diode follow ohms law
No
Required practicals - Ohms law in different components
Why doesn’t a diode follow ohms law - draw a graph of it with respect to voltage and current
It has very high resistance in one direction, so current is zero there. It also high high resistance at low potential differences, which means current stays low initially
Required practicals - Ohms law in different components
What is one hazard which is pretty much universally applicable when talking about investigations
Hazard - hot wire
Consequence/risk - burns skin
Precaution / control measure - don’t touch the wire when the circuit is connected and allow it to cool
Exam - Required practicals - Ohms law in different components
How do you structure questions that ask about how to minimise risk or take precautions in experiments
To prevent (risk) … which would cause (hazard) … we should (preventative measure) …
Plugs + mains
What are pins made of in a plug? Why?
Brass - tough, durable, conducts electricity, doesn’t rust!!!
Plugs + mains
What are wires made of?- why?
Copper - conducts electricity, bends and is ductile, cheaper than alternatives like gold
Plugs + mains
What is the casing of a plug made of - why?
Plastic - doesn’t conduct (insulator), durable and tough
Plugs + mains
What colour is an earth wire
Striped yellow and green
Plugs + mains
What is the colour of a neutral wire
Blue
Plugs + mains
What is the colour of a live wire
Brown
Plugs + mains
Where does the earth wire go
Top - think striped (see. Mindmap)
Plugs + mains
Where does the live wire go
Right - see mindmap for rule
Plugs + mains
Where does the neutral wire go
Left - see mindmap for rule
Plugs + mains
What are the 3 main ratings of fuses
3 A, 5 A and 13 A
Plugs + mains
What is the rating of a fuse
The maximum current that can go through a fuse without it blowing
Plugs + mains
What is it called when a fuse heats up and melts
The fuse has blown
National grid
What is the first stage of the grid (and bonus for its voltage)
Power station - 25kV
Plugs + mains
What is a step up transformer and why does it do what it does
Increases voltage, decreasing current to make the system more efficient - as it prevents energy dissipating into the surroundings
Plugs + mains
True or false: pylons and cables have high current and low voltage - with a voltage of 132 kV
False (it is the opposite) - however the voltage is still 132 kV
Plugs + mains
What does a step down transformer do and why?
Increases current and decreases voltage, to make voltage safe
Plugs + mains
What is the voltage of the mains
230V
Plugs + mains
What is a power station definition
Generates electricity which is then transported around the country
Plugs + mains
What are pylons
They support electric cables
Plugs + mains
What do cables do
Transports electricity around the country
Plugs + mains
What is the role of transformers
Increases and decrease voltage at particular stages in the national grid
Plugs + mains
Give 3 pros of overhead cables
Cheap and efficient, easy to repair, can cross roads and canals easily
Plugs + mains
What are 3 cons of overhead cables
Visual pollution, prone to decay, takes up space
Plugs + mains
What is one pro of underground cables and find a bonus one
No visual pollution - and decays less easily than overhead cables
Plugs + mains
What are 3 cons of underground cables
Expensive, difficult to repair, difficult to bury around canals and roads
Static electricity
What is static electricity
Charge that accumulates on insulators due to forces like friction
Static electricity
How can static electricity be produced?
Rubbing materials together - this means some negative charge is lost from one material as it is dislodged by the force of friction, and given to another
Static electricity
Which way does a positive electric field point
Outwards