SP10 - Electricity and Circuits ✓ Flashcards
(46 cards)
1
Q
SP10a - Descrbe what a potential difference is.
A
The force that pushes the electrons to flow around the circuit.
2
Q
SP10a - Describe the structure of an atom including features of the sub-atomic particles.
A
- Proton and neutron in the nucelus, each with a relative mass of 1.
- Protons have a charge of +1.
- Electrons orbit in energy levels each with a charge of -1 and a relative mass of 1/1835 (negligible)
3
Q
SP10a - What are the two types of circuits?
A
- Series: everything connected in one route
- Parallel: many options for different routes.
4
Q
SP10a - What is conventional current?
A
What we refer to as the direciton of current form positive to negative. Opposite to the flow of electrons.
5
Q
SP10a - Why may parallel circuits be more beneficial?
A
- If the circuit becomes incomplete along one path, the rest of the circuit can still continue to function. (e.g - Switches can be connected to different parts meaning lights in parallel to each other can be switched in and off individually)
- If a bulb goes off, the rest of the circuit in parallel to this can still continue to function
6
Q
SP10b - How does potential difference differ in parallel and series circuits?
A
- S: The p.d is different across different components, directly proportionate to the resistance of that component
- P: The p.d is the same at all points across the circuit
7
Q
SP10b - How does total current differ in parallel and series circuits?
A
- S: The total current is the same at all points throughout the circuit
- P: The total current gets split between the branches of the circuit, inversely proportionate to the resistance of the components in those branches.
8
Q
SP10b - What is the unit for current and how can it be measured?
A
Amps (Amperes). Measured using an ammeter which is attached in series to the circuit
9
Q
SP10b - What is the unit for potential difference and how can it be measured?
A
Volts. Measured using a voltmeter which is attached in parallel to the component you are measuring the potential difference of.
10
Q
SP10b - What two conditions are required for current to flow?
A
- The circuit must be closed
- It must contain a source of potential difference
11
Q
SP10c - Describe potential difference in terms of Joules per Coulomb
A
- The potential difference of a cell is the amount of potential energy the cell transfers to each coloumb of charge passing through it
12
Q
SP10c - What equation links energy and charge and how can this be changed to link energy to current?
A
E = Q x V (Energy = Charge x p.d)
since Q = I x t, this means that
E = I x t x V (Energy = Current x time x p.d)
13
Q
SP10c - What is current?
A
- The flow of electrons
- The rate of flow of charge
14
Q
SP10c - What is the equation linking charge and current?
A
Q = I x t
(Charge = Current x time)
15
Q
SP10c - What is the unit for charge?
A
C - Coulombs
16
Q
SP10d - How do you calculate the resistance in series and parallel circuits?
A
- Series: Add up the resistance of all the components
- Parallel: 1/RT = 1/R1 + 1/R2 + ………..
17
Q
SP10d - What is key to remember about the size of the total resistance in series and parallel and series circuits?
A
- S: It is greater than any of the individual resistances
- P: It is smaller than all of the individual resistances
18
Q
SP10d - What is Ohm’s law?
A
V = I x R
(p.d (V) = Current (A) x Resistance (Ω))
19
Q
SP10d - What is resistance?
A
The force pushing back against p.d opposing and reducing the current.
20
Q
SP10e - Describe what a graph for resistance of a thermistor would look like and why.
A
- The x-axis would be temperature (°C) and the y-axis would be resistance (Ω)
- As the temperature increases, the resistance decreases. This forms a negative curve in an L shape.
- This can be used to reduce the current in lower temperatures.
21
Q
SP10e - Describe what a graph for resistance of an LDR (Light-dependant resistor) would look like and why.
A
- The x-axis would be light intensity (lux) and the y-axis would be resistance (Ω)
- As the light intensity increases, the resistance decreases. This forms a negative curve in an L shape
- This is used for lit up signs outside. In darker conditions (lower light intensity) bulbs don’t need to be as bright.
- Thus, the resistance is higher to reduce the current and brightness
22
Q
SP10e - What does a IV graph for diode look like and why?
A
- A line that is nearly on the x-axis till it shoots up.
- This is because a diode has low resistance if the potential difference is in one direction but a very high resistance if the potential difference is in the opposite direction
23
Q
SP10e - What does a IV graph for filament lamp look like and why?
A
- An S shaped ‘curve’.
- The current causes the filament to heat up and glow - the greater the p.d, the more current flows and the hotter and whiter the filament gets. However, as it heats up, the filament’s resistance increases. Therefore, the voltage and current are not in direct proportion anymore
24
Q
SP10e - What does a IV graph for fixed resistor look like and why?
A
- It is a straight diagonal line showing direct proportion.
- This is because resistors are ohmic conductors.
- The voltage is directly proportionate to the current.
25
SP10e - What does the gradient of an IV graph represent?
The inverse of the resistance (1/R)
26
SP10e - What is an ohmic conductor?
A component in a circuit that follows Ohm's rule of V=IxR
27
SP10e CP - Describe your set-up for an experiment to compare the relationship of V=IxR in a resistor, and a filament lamp in parallel/series.
**_Fixed Resistor_**
* Set up a series circuit, with an ammeter and voltmeter. The voltmeter should be connected in parallel to the fixed resistor.
* We vary the values of the voltage, and note down the current at each voltage
* Take these readings straight away to ensure the wire doesn't get too hot and results become inaccurate
* Plot a graph, with current on the y axis and voltage on the x axis
Replace the resistor with a filament lamp then do the same
28
SP10f - Describe what resistance is in terms of a metal's structure.
* Current is the flow of electrons.
* A metal is made of electrons flowing around positive metal ions
* When the electrons are moving in the circuit, they can collide into these posistive metal ions.
* These collisions are resistance and they transfer energy
29
SP10f - How can resistance be reduced in a circuit?
* Choosing a metal with a lower resistance, e.g copper
* Using a thicker wire (more space for electrons to flow)
* Using a shorter wire (less distance in which they can collide)
30
SP10f - What formula links energy, time and voltage?
E = I x t x V
Energy = Current x time x Voltage
31
SP10f - What is the heating effect?
* The heating effect is when a circuit warms up due to the resistance in its wires.
* Work is done against the resistance and so energy is transferred.
* This is in the form of heating and dissipates into the surroundings
32
SP10f - Where is the heating effect useful?
* In appliances such as electric heaters and kettles where the aim is to use thermal energy, the heating effect is incredibly useful.
* In these circuits, resistance tends to be high.
33
SP10g - How do you form the the equations that link Power and Resistance?
* We know that P = I x V and that V = I x R
* If we substitue the V in the first equation we get P = I x I x R or P = I² x R
* If we rearrange V = I x R we get I = V ÷ R
* So if we substitute this in we get P = V x V ÷ I or P = V² ÷ R
34
SP10g - What are the four formulae for power?
* P = E/t
* P = I x V
* P = I² x R
* P = V² ÷ R
35
SP10h - What are the differences between d.c and a.c?
**d.c**:
* Only one direction (positive to negative)
* Electrons loose energy as they travel from positive to negative
* A grpah showing the direction will only ever be on one side of the x-axis
**a.c**:
* Constantly switching direction (this is their frequency)
* Electrons vibrate and pass on energy
* A graph showing direction will contantly cross zero and over the x-axis
A̶C̶/̶D̶C̶ ̶a̶r̶e̶ ̶a̶n̶ ̶A̶u̶s̶t̶r̶a̶l̶i̶a̶n̶ ̶r̶o̶c̶k̶ ̶b̶a̶n̶d̶ ̶f̶o̶r̶m̶e̶d̶ ̶i̶n̶ ̶S̶y̶d̶n̶e̶y̶ ̶i̶n̶ ̶1̶9̶7̶3̶ ̶b̶y̶ ̶b̶r̶o̶t̶h̶e̶r̶s̶ ̶M̶a̶l̶c̶o̶l̶m̶ ̶a̶n̶d̶ ̶A̶n̶g̶u̶s̶ ̶Y̶o̶u̶n̶g̶.̶
36
SP10h - What the voltage and frequency of and type of electricity that comes through mains supply?
* 230V
* 50Hz (changes diretion 50 times per second)
* a.c
37
SP10i - Describe the five features of a 3-pin plug.
* **Live wire**: Connects the appliance to the generators at the power station providing 230V
* **Neutral wire**: The return path to the power station and will be at 0V if circuit is correctly connected
* **Earth wire**: Connects the metal parts of the appliance to a large spike of metal that pushes down and connects to the ground. It is for safety and is at 0V if the circuit is correctly connected
* **Fuse**: A Safety device usually 3, 5 or 13 A
* **Plastic casing**: This electrical insulator allows you to safely hold the plug
38
SP10i - How do you choose the best value for a fuse?
* Fuses are typically found in 3A, 5A, and 13A.
* You want to pick one that has a current higher than what the current of the appliance is but not too high.
* This way it will stop a faulty appliance but not a properly functioning one.
* If an appliance has a current of 3A, you would pick a 5A fuse. 3A would be too low and 13A would be too high
39
SP10i - How does a fuse provide safety? (Describe this though it's structure)
* A fuse is a glass tubing with a thin metal wiring that the electricity passes through.
* A faulty appliance may draw too much current which would heat up and cause a fire.
* However depending on the value of the fuse, it will melt once the current has reached a certain level and cause the circuit to be incomplete meaning current stops flowing through it
40
SP10i - How does an earth wire make an appliance safer?
* If a wire comes loose and touches the metal part of the appliance, the electricity will be able to flow through this.
* When a person touches it, the electricity can pass through the person to the ground.
* This would give them an electric shock.
* However the earth wire provides an easier way to travel to the ground.
* As electrcity always takes the path of least resistance, it goes this way and the person doesn't get an electric shock
41
SP10i - What are circuit breakers and how do they work?
* Circuit breakers are automatic swtiches that detect a rise in current and automatically switch off the supply safely.
* They are an alternate to fuses.
42
SP10i - What are the colours of the earth, neutral and live wires?
* Earth wire: Green and yellow
* Neutral wire: Blue
* Live wire: Brown
43
SP10i - Why are circuit breakers more advantageous than fuses?
* They can just be turned back on rather than having to buy a new fuse
* They work quicker.
* You elliminate the risk of an accident occuring while the fuse is melting
44
SP10i - Why may fuses be more advantageous than circuit breakers?
* Fuses are cheaper
* More practical for small scale uses (e.g. small appliances)
45
SP10i - Explain the danger of a connection between the live wire and Earth
* If a fault causes the live wire to touch a metal part, it makes a very low resistance circuit between 230V and 0V.
* This causes a very large current to flow to the Earth, which heats up the wire and could cause a fire. If this happens, the current blows the fuse and cuts off the mains.
46
SP10e CP - Outline the steps of the parallel/series circuit investigation, involving filament lamps
1. Set up a series circuit with two filament lamps, both with voltmeters connected in parallel.
2. Slowly increase voltage, note the current
3. Set up a second circuit, parallel and record the voltage/current for both
4. Compare the two arrangements, their total resistance, the voltage across each lamp etc.
