P2 Flashcards
Voltmeter
measures the potential difference across a component
Ammeter
measures current
Battery / Cell
Provides energy to the electrons in a circuit
Switch
Connects / Disconnects the circuit
Resistor
Resists current
Diode
Keeps current flowing in one direction
Thermistor
- Resistance decreases as temperature increases
- When temperature increases, additional energy can be used to increase the kinetic energy of electrons (current)
- More current = less resistance
Light Dependant Resistor
Resistance decreases as light increases
- When light increases, additional energy can be used to increase the kinetic energy of electrons (current)
- More current = less resistance
Voltage
Amount of energy supplied to each Colomb
Potential Difference
- The difference in energy per charge between 2 points in a circuit
- Shows how much energy is supplied to a component
- YOU ALWAYS CALCULATE THIS
Current Calculation?
Current = Charge / time
Energy Calculation?
Energy = Charge x Potential Difference
Current in a series circuit…
Always stays the same
Current in a parallel circuit…
Splits between the pathways
Potential Difference in a series circuit…
Is shared amongst the components
Voltage in a parallel circuit…
Stays the same
More resistors in series…
= more resistance
More resistors in parallel…
= more pathways = more current = less resistance
Ohms law
- Current flowing through a resistor is directly proportional to the potential difference
- Current across a resistor is inversely proportional to the resistance
What is the only condition for ohms law?
If Temperature is Constant
Resistance in Parallel circuit?
- Total resistance is always less than the lowest resistance in the circuit
- Rt = 1 + 1
R1 R2
What is the gradient on a V-I graph for a resistor?
Resistance
If a component obeys ohms law what WILL be constant?
Resistance
Does a filament Bulb follow Ohm’s law?
- Up to a certain point where the line starts to curve
- This is because after a while, temperature increases which leads to more resistance leading to less current
Why does temperature affect resistance?
- Inside wires are delocalised electrons that carry a charge
- Increase in temperature = more kinetic energy
- more electrons collide with cations
- Which delays current, slowing is down
- Which is resistance
Do diodes follow Ohms’s law?
- No, resistance isn’t constant
- A Diode has low resistance in one direction and high resistance in the other direction
(The current through a diode flows in one direction only. The diode
has a very high resistance in the reverse direction.)
Why are people rarely electrocuted by appliances?
- Use plastic around wires
- Plastic is an insulator; cant carry electricity
- Fuse
What is double insulation?
An appliance with a plastic case is double insulated
What are wires made from and why?
- Copper
- Bends easily
- Group 3: for every ion, there are 3 delocalised electrons which can carry more overall energy
- Light
What are pins made from and why?
- Brass
- Not very reactive (doesn’t rust)
- Doesn’t bend
- Good conductor
Why is the diameter of a wire important?
- Wider diameter = more current = less resistance
- May overheat
Why do we use Plastic to cover the wires?
- Good insulators
- colours make it easy to label wires
What are the wires and their colours?
live wire – brown
neutral wire – blue
earth wire – green and yellow stripes.
What does the live wire do?
Carries the potential difference (230V) from the supply
What does the earth wire do?
An earthing/grounding system connects certain parts of an electric system to the ground to absorb the current
What is the Neutral wire for?
- Completes the circuit
- If it gains voltage the earth wire will be used
- Voltage should always be 0
Fuse
A component with a wire running through it, which is melted when there is too much current
Why do you want your fuse to be more than the current that you have?
Anything more than the current will blow the fuse
Where is the fuse in the circuit?
Between the live wire and the appliance so that if a fuse blows, the appliance is cut off from the live wire supply
What are circuit breakers
If they notice an increase in current to the fuse a switch will trip (open), stopping the flow of current
Why are circuit breakers better than fuses?
- Notice a very slight difference in current, whereas fuses only notice a 3 Amp difference
- Can be reset easily, unlike fuses which need to be replaced
Power equations?
Power = current x potential difference
Power = Resistance x current^2
What is power?
Amount of energy transferred / second to the electrons
Genortaor?
Generates electricity which is transported around the country
Pylon?
Supports the elctric cables
What holds the wires together
Cable grip
Cables
Transport electricity around the country
Transformer
Increases/decreases voltage at particular stages in the national grid
Calculations for the amount of energy transferred to appliances?
Energy = Power x Time
Energy = Charge x Potential Difference
Why is the national grid efficient?
- Uses step-up transformers to increase the potential difference which makes current decrease to keep power constant: which limits the collisions between the electrons and cations which creates wasted thermal energy (high current = cables get hot)
- Uses step-down transformers before it reaches your home to decrease the potential difference so it doesn’t kill you
- It’s efficient since it limits energy wasted
Pros and Cons of Underground Cables?
P Doesnt affect landscape
P not affected by weather
C Expensive
C Difficult to put
C High Maintenence
C Cause damage if breaks
Pros and Cons of Overhead Cables?
P Higher Voltage
P Easier to repair
P Cheaper
C Affected by weather
C Heat dissaptaion
Alternating Current
Current is continuously changing directions
Static Electricity
