Components of a Circuit (P2) Flashcards
Define Battery
Two or more cells.
Define Current
The rate of flow of electric charge.
Define Circuit
Two or more components that link to make something happen using electricity.
Define Series
One main circuit where electricity can only flow through one route.
Define Diode
Only allow electricity to flow in one direction and above a certain threshold.
Define Resistor
Limits quantity of flow.
Define Variable Resistor
Limits quantity of flow and can be adjusted.
Define Fuse
Breaks a circuit with too much current.
Define Voltmeter
Measures the potential difference between two points in a circuit.
Define Ammeter
Measures the current in a circuit.
Define Thermistor
Limits quantity of flow dependant on temperature.
Define LDR
Limits quantity of flow dependant on light.
Define Electron
Charged particles that move around a circuit.
Define Insulator
Materials, such as rubber/plastic, which do not conduct electricity.
What is charge?
Charge (Q)
Charge is measured in Coulombs (C)
Charge is a property defined by quantity of protons (+) vs electrons (-)
What is current?
Current (I)
Current is measured in Amperes (A)
Current is the rate of flow of electric charge.
Total Charge (using current and time)
Total Charge = Current × Time
Columbus (C) = Amperes (A) × Seconds (s)
Q = It
Potential Difference (using current and resistance)
Potential Difference = Current × Resistance
Voltage (V) = Amperes (A) × Ohms(Ω)
V = IR
What direction does ‘conventional current’ flow in?
‘Conventional current’ travels from positive to negative. (This is the flow of protons)
What does the rope model show?
- Current is felt instantly when the power is applied no matter where electrons in the circuit are.
- Electrons are constantly in the wire with or without power.
What makes insulators and conductors good at their jobs?
Insulators - High Resistance
Conductors - Low Resistance
Insulators have more obstacles for charged particles to pass through.
What does it mean for resistance if there are many free electrons?
The more free electrons, the lower the resistance.
What is a multimeter and how does it work?
Multimeter = ammeter + voltmeter + ohmmeter
One wire always goes in the COM input
One wire goes into 10A (if measuring current) or into VΩ (if measuring potential difference or resistance).
How do you calculate resistance when plotting current and potential difference on a graph?
With Current on y axis and voltage on x axis.
Calculate the gradient (Change in y/ Change in x)
V=IR so R=V/I and Gradient=I/V
Therefore, if you reciprocate the gradient, you get resistance.
This is because the gradient and resistance are inversely proportional.
When Voltage increases what happens to Current?
Voltage increase = Current increase
Why are long wires not ideal?
Due to more obstacles in long wires, resistance increases.
What happens to current and voltage in a series circuit?
Current in any point is the same and voltage is shared between any components.
What happens to current and voltage in a parallel circuit?
Current is shared around the circuit and voltage is the same everywhere.
What happens to the amount of resistance in a parallel circuit when resistors are added?
Resistance decreases when more resistors are added into the circuit. Adding a wire with no resistance could cause a component on another parallel to stop working.
What happens to the amount of resistance in a series circuit when resistors are added?
Total resistance is the sum of the individual resistors. Resistance increases when more resistors are added.
Why might a filament lamp given a different resistance graph (of current vs potential difference) than an LED?
A filament bulb gets hot and an LED doesn’t. The hotter the atoms, the more they move and thus interfere with passing, charged electrons, therefore, there is more resistance as they get hotter. This does not happen for LEDs. Therefore the graph for an LED is linear but that of a filament bulb flatness at the bottom and top and increases in gradient around the middle.
Amperes split across parallel branches…
adds up to the total amps at the start of the circuit but it does not always split evenly
What does an ammeter measure?
Flow of electric charge
Current
What happens to current in a series circuit?
Same everywhere
What happens to current in a parallel circuit?
It is split across the branches
All the branches add up to the current entering/ leaving the cell
What direction does conventional current flow in?
Positive to Negative
Describe the transfer of energy around a circuit
The cell gives the electrons chemical energy which becomes electrical energy. When this passes through components it changes store again.
Define Potential Difference
How many joules of energy there is for each coulomb of charge
1 volt =….
1 joule of energy for every coulomb of charge
How do we measure Potential Difference
Voltmeter
What happens to Potential Difference in series?
It is shared between the components
Calculate the rate of flow of electric charge
Q=It
Charge (C) = Current (A) x time (s)
What is electrical charge?
The size of the electrical current is the rate of flow of electrical charge
What is the other term for Energy Transferred?
Work Done
Calculate Energy Transferred (J)
related to charge
E=Qt
Energy (J) = Charge (C) x time (s)
Define Resistance
The opposition in an electrical component to the movement of electrical charge through it.
Calculate Resistance
R = V/I
(V=IR)
Resistance (Ω) =Voltage
(V)/ Current (A)
Why would we use a resistor?
Change the brightness of a lamp
Lower the sped of a motor etc…
What does the graph for resistance of an ohmic conductor look like?
Potential difference on the x axis and Current on the y axis
The resistance increases in a straight line passing through 0,0 as long as the temperature is constant
What does the graph for resistance of a filament lamp look like?
Potential difference on the x axis and Current on the y axis
Resistance starts at a low gradient then increases to steady and then begins to slow again. It passes through 0,0.
Why does resistance change in filament lamps?
Because as they heat up the particles move more and there is more resistance
What does LED stand for?
Light Emitting Diode
What do LEDs do?
Only allows current to flow in one direction
When current flows through, it emits light
Why are LEDs useful?
Very energy efficient
How do diodes work?
High resistance in the opposite direction
What does the graph for resistance of a diode look like?
Potential difference on the x axis and Current on the y axis
Resistance is 0 in the negative an only begins increasing at 0,0 (or above a specific threshold)
Resistance in series…
Adds up
Resistance in series=
Total = R1 + R2….
Resistance in parallel…
the total is less than the smallest resister
What does LDR stand for?
Light Dependant Resistor
What is the resistance of an LDR when it is bright?
Low
What is the resistance of an LDR when it is dark?
High
What happens to a thermistor at high temperature?
Low Resistance
What happens to a thermistor at low temperature?
High
Give an example of a useful LDR
Night - time garden lamp
Give an example of a useful thermistor
Cooling in a laptop
How do we investigate the impact of wire length on a circuit?
Put a wire on a meter ruler
Connect crocodile pins at 0cm and 10cm
Connect these to a circuit
Measure the current and potential difference in the circuit and calculate resistance
Repeat with the same circuits but different lengths, switching the power off in between readings to allow the circuit to stay cool
Plot a Length of Wire vs Resistance graph, subtracting the zero error
Define Zero Error
A reading on a measuring instrument when the value should be 0
It is a systematic error that cannot be reduced by carrying out repeats
What causes the zero error when investigating the effect of wire length on resistance?
Resistance between crocodile clip and wire
Crocodile clip not perfectly at 0
How can we minimise heating effects when investigating the effect of wire length on resistance?
Use a low potential difference
Only turn it on when taking a reading
Why is it important to have less heating effects when investigating resistance?
Heat increases resistance
How does resistance change in a variable resistor?
We can increase the length of the wire, increasing resistance or vice versa
Define Power
Rate at which energy is transferred
1 watt is an energy transfer of…
…1 joule per second
Appliances which are designed to generate thermal energy have much ……… power ratings than those which generate kinetic energy
Higher
Calculate Energy Transferred (J)
related to power
E=Pt
Energy (J) = Power (W) x time (s)
Calculate Power (W) (with potential difference)
P = IV
Power (W) = Current (A) x Potential Difference (V)
Calculate Power (W) (without potential difference)
P = I^2R
Power (W) = Current ^2 (A^2) x Resistance (Ω)
P = I^2R and P = IV are used for what?
To calculate the power of components/ appliances
Define AC current
Current that is constantly changing direction
What does AC stand for
Alternating Current
Define DC current
Electrons only travel in one direction
What does DC stand for
Direct Current
Give an example where AC is used
Energy mains
Give an example where DC is used
Battery
What are Hz?
The amount of times AC current switches direction per second (frequency)
What frequency do mains electricity have in the UK?
50 hertz (Hz)
What potential difference do mains electricity have in the UK?
230V
What is the advantage of using AC instead of DC?
Works with transformers in the electricity mains, can travel further
What is an oscilloscope?
A machine used to see the pattern of current
What does an oscilloscope trace look like for DC
Stays the same
What does an oscilloscope trace look like for AC
Waves
How do we calculate the frequency of AC using a oscilloscope trace?
Calculating the number of cycles per second (distance between peaks)
What type of wire do most UK appliances use?
Three-core cable wire
What is the brown wire in a three-core cable wire?
Live wire
Carries the alternating potential difference from the supply (230V)
What are most three-core cable wires made of and why?
Copper - Conductive
Plastic covering - Non Conductive
Can conduct but not dangerous to touch
What is the live wire also connected to for safety?
A fuse
What is the blue wire in a three-core cable wire?
Neutral
Completes the circuit
What potential difference does the live wire carry?
230V
What potential difference does the neutral wire carry?
0V
What is the green and yellow stripe wire in a three-core cable wire?
Earth
For safety
What may happen if a live wire comes loose and touches a metal casing?
(assuming nothing else is involved)
The casing becomes live and if anyone touches it, it will electrocute them (probably fatally)
Why should the live wire not be touched even when the switch is open
Some parts still have potential difference (230V) which could prove fatal
What is the function of the earth wire?
It is connected to any metal cases and is connecter to the ground with a rod to instantly ‘earth’ any charge safely
What is the function of a fuse?
If a huge current flows to the Earth, the fuse melts and cuts off the current
What are the percentages of fuel sources in the UK?
> 50% Fossil Fuels
25% Renewables
20% Nuclear
(the rest is imported)
Describe the components energy transfers through in the National Grid
(Starts in a power station,) Goes through a step up transformer, Goes through high voltage cables, Goes through a step down transformer, (Goes into homes.)
What is the largest issue with the long energy transfer in the National Grid?
Energy is always lost in the power cables due to resistance of the wires
What are the two ways of reducing energy loss in the National Grid?
Build power stations near homes
Use transformers
What does a step-up transformers do?
Increases potential difference to several hundred thousand volts - current decreases
(less energy lost through the cables)
Why are step-down transformers also needed?
Voltage is too high
What does a step-down transformers do?
Decrease voltage to about 230V - current increases
Define Static Electricity
Electricity created by the movement of electrons from one insulator to another, making one positive and the other negative
What does it mean to be a good conductor?
Electrons can easily go through - metals
What are insulators?
Materials electrons cannot easily go through
Cloth is an insulator. Like everything, it is covered in….
Electrons which cannot move through the cloth
What makes our hair stand on end with a van der graff generator?
The top of the generator is positive due to the plastic roller loosing electrons to the belt. (these are earthed at the bottom)
If someone holds onto this, they become positive and the hairs (also positive) now repel
What is a danger of static electricity?
Sparks
Objects with different charges…
Attract
Objects with similar charges…
Repel
Objects that are attracted to each other feel what force?
Force of attraction (non-contact)
Objects that are repelled by each other feel what force?
Force of repulsion (non-contact)
Energy field lines are always…. to a charged object?
Perpendicular
If two charged objects are close, what happens to the force between them?
Becomes stronger
If two charged objects are far apart, what happens to the force between them?
Becomes weaker
What do field lines look like?
Perpendicular to an objects surface
Have arrows to show the direction of the force
Lines extend past the arrow
