| What does the high voltage transmission lines do in the national grid? | They carry the current over long distances. The power dissipated by the wires obey P- |
| What does the high voltage transmission lines do in the national grid? | They carry the current over long distances. The power dissipated by the wires obey P- |
| What does the high voltage transmission lines do in the national grid? | They carry the current over long distances. The power dissipated by the wires obey P- |
| What does the high voltage transmission lines do in the national grid? | They carry the current over long distances. The power dissipated by the wires obey P- |
| What is an electric current? | The flow of electric current around a circuit. |
| What is potential difference? | This is also called voltage which is the driving force that pushes charge. |
| What is resistance? | Anything in the circuit which slows the flow down. Its unit is ohms. |
| What does the current flowing through a component depend on? | The potential difference across it and the resistance. |
| What is the formula for total charge? | Charge (Coulombs) = Current (Amperes) × Time (Seconds)
Q = I × T |
| What is a cell? | Something that converts chemical energy. |
| What is a battery? | Two or more cells connected together. |
| What is a switch? | When its open, the circuit is broken. When the switch is closed the electric circuit works. |
| What is a filament lamp (bulb)? | A thin wire that heats and lights up when an electrical current passes through. |
| What is a fuse? | Something that breaks the current by melting. |
| What is a LED? | Light emitting device. |
| What is a a Resistor? | Something that regulates electrical flow. |
| What is an ammeter? | Something that measures electrical current in amperes. |
| What is a diode? | Something that allows current to flow in one direction. |
| What is a LDR? | Light dependent resistor. |
| What is a variable resistor? | Something that allows electrical resistance to be adjusted. |
| What is a voltmeter | Something that measures voltage. |
| What is the formula for potential difference?
(Energy and Charge) | Voltage (V) = Energy (E) ÷ Charge (Q) |
| How much energy is transferred if 2.5 coulombs flows through a component when 5 volts is applied across it? | E = QV
> 2.5 × 5 = 12.5J |
| What is resistance and what is it measured in? | A measure of how hard it is for the current to pass through a component in a circuit.
It's measured in ohms (Ω). |
| What is the equation that links potential different and resistance? | Voltage (V) = Current (A) × Resistance (Ω) |
| A voltmeter reads 6 V and a resistor is 4 Ω. What is the current through an ammeter? | V = IR -> I = V ÷ R
> 6 ÷ 4 = 1.5 A |
| What happens to the resistance of ohmic conductors? | The current flowing will be directly proportional to the potential difference across it, so the resistance doesn't change with he current.
R is contant in V = IR. |
| What happens to the resistance in non ohmic components like bulbs? | When an electrical charge flows through a filament lamp, some energy is transferred to thermal energy stores.
The resistance increases with the temperature, so as the current increases, so does the resistance. |
| What is the formula for ohms law? | Voltage (V) = Current (A) × Resistance (Ω) |
| What is the formula for power in electrical circuits? | Power (W) = Current (A) × Potential Difference (V) |
| What is the formula that connects both ohms law and power? | Power (W) = Current² (A) × Resistance (Ω) |
| Calculate the power through a component if the current through it is 5A, and its resistance is 2.5Ω. | P = I² × R
> 5² × 2.5
= 62.5 watts |
| What is the formula when you combine the equations, P = I × V and P = E ÷ t? | P = I × V
> I × V = E ÷ t
Power = I × V, but Power also = E ÷ t. That means they both equal each other.
> I × V = E ÷ t
×t ×t
= I × V × t = E
Current × Volts × time = Energy |
| What is the formula when you combine Specific Heat Capacity and Power/ Energy? | E = M × C × △t
÷M△t ÷M△t
> E ÷ M△t = C
= I × V × t ÷ M△t = C
I × V × t is the equation for energy, so you can use this for E if you don't have it. |
| What are the different sources of errors in practicals? | Random errors, Systematic errors and zero errors. |
| What are random errors? | Errors that cause readings to be spread out around the true value, due to results varying from unexpected and uncontrolled errors. |
| How do random errors happen? | These errors are present when measurements are made. |
| How can you prevent random errors? | You can prevent these errors by repeating the experiment so that your answer will be an average and more accurate. |
| What are systematic errors? | Errors that cause readings that are different to the true value to be consistent each time. |
| How do systematic errors happen? | The source of this error may be the environment, method of observation, or the instruments used. |
| How can you prevent systematic errors? | You can prevent these errors by collecting data with different techniques and equipment, then comparing the results. |
| What are zero errors? | These errors are present when the measuring systems - ammeters, voltmeters and etc - give false values when the true value is zero, resulting in systematic uncertainty. |
| What is a series circuit? | A circuit with only one loop or branch. This means that there is only one way for current to flow. |
| What is a parallel circuit? | A circuit with more than one loop or branch. This means that there are multiple routes for current to flow. |
| What happens to the current in a series circuit? | The current stays the same at all points. |
| What happens to the potential difference in a series circuit? | The potential difference is shared through the components. This means that it will add up to be the same sum as the total voltage. |
| What is potential difference? | The energy per unit charge given by a power source. |
| What is the formula for potential difference? | V = I × R
Voltage = Current × Resistance |
| What happens to the resistance if voltage increases? | The higher the voltage, the higher the resistance. |
| What happens to the resistance in a series circuit? | The resistance adds together to make the total resistance. It's the opposition to current flow. |
| A series circuit has a 2Ω resistor, and a 3Ω resistor, and the total potential difference is 1.5V. What is the;
1. Current
2. Total resistance
3. Potential difference | 1. Current = V ÷ R
> 1.5 ÷ 5 = 0.3A.
2. Total resistance is 2Ω + 3Ω, this equals 5Ω.
3. Total potential difference is1.5V. |
| What happens to the current in parallel circuits? | The current splits at a junction, and rejoins when the wires rejoin. |
| What happens to the potential difference in parallel circuits? | The potential difference is the same at all points and branches. |
| What happens to the resistance in parallel circuits? | The resistance adds up to be the total resistance, but it decreases by adding more branches and the total resistance will be lower than the lowest value resistor. |
| What is the formula to work out total resistance in parallel circuits? | 1/Resistor1 + 1/Resistor2 ...
> 1/Total Resistance = 1/Resistor1 + 1/Resistor2..
> x/Total resistance = Total resistance/x |
| What is the total resistance of a parallel circuit with a 3Ω resistor and a 4Ω resistor? | 1/3 + 1/4
> 7/12
= 12/7Ω |
| What is resistance? | It is a measure of how hard it is for electrons to pass through. |
| What happens to the resistance if the wire is hot? | The resistance will increase because the electrons will experience more collisions. |
| What happens to the resistance if the wire is thin and long? | The resistance will increase because there will be more collisions. |
| What is the heating effect? | Collisions cause heat, and more heat create more collisions and resistance, creating a loop. |
| What is the dependent variable? | The resistance (V÷I). |
| What is the independent variable? | The length of the wire. |
| What us the control variable? | The temperature of the wire, this is because if it increases, the resistance will also increase and change. |
| What is an IV graph? | A graph that shows the relationship between current and voltage. |
| How is negative potential difference achieved? | When a cell or battery is reversed. |
| What does an Ohmic Conductor IV graph show us? | It shows us that voltage and current are directly proportional. It's typical with a fixed resistor, and the steeped the gradient, the less resistant. |
| What does a Filament Lamp IV graph show us? | It shows us that it's non-ohmic and as voltage and current increase, the temperature also increases, so the resistance increases too. |
| What does a Diode IV graph show us? | It shows us that it has a threshold voltage, and current can only flow above this voltage. |
| What does a LDR IV graph show us? | It shows us that the resistance of a LDR decreases with increasing light intensity. |
| What does a Thermistor ID graph show us? | It shows us that the resistance of a thermistor decreases with increasing temperature. |
| What is direct current (d.c)? | Current that only flows in one direction, this happens from cells or batteries. |
| What is alternating current (a.c)? | Current that is constantly changing direction, this happens in your homes. |
| What is mains electricity? | The electricity generated by power stations and transported around the country through the National Grid.
It is 230V A.C with a frequency of 50Hz. |
| What does a frequency of 50Hz mean? | The frequency tells us that the electrons are constantly changing direction 50 times each second. |
| What are the different components of a 3-pin plug? | The earth wire, neutral wire, live wire, fuse, cable grip and outer insulation. |
| What are the pins made out of in a plug, and why? | They are made out of brass because it's durable and conducts. |
| What does the live wire do and what colour is it? | The live wire is brown and it carries the a.c. It has a high voltage. |
| What does the neutral wire do and what colour is it? | The neutral wire is blue and it completes the circuit. |
| What does the earth wire do and what colour is it? | The earth wire is green with yellow stripes and is a safety wire. It is usually only in metal appliances. It only carries current if there's a fault. |
| What material are the wires usually covered in and why? | They are usually covered in flexible rubber or plastic to keep heat in since they're insulators, and to prevent electrocution. |
| What is a circuit breaker? | An electrical switch that stops the circuit, it's used instead of a fuse because it doesn't need to break to stop the circuit. |
| What is an oscilloscope? | A piece of equipment that measures and shows voltage over time. |
| What is discrete data? | Data that has set values. E.g. eye colour or gender. |
| What is concrete data? | Data that can have multiple values. E.g. weight or height. |
| What do the step-up transformers do in the national grid? | They change the amount of potential difference, increasing it to about 132,000 volts to minimise dissipation. But this means it has low current flow. |
| What is the national grid? | A network of cables that distribute electricity from power stations to buildings. |
| What is a disadvantage of communities having their own power source instead of the national grid?9 | If there was a shortage, communities would be unable to accommodate others' needs. |
| What do the step-down transformers do in the national grid? | They change the amount of potential difference, decreasing it to about 230 volts so it can enter homes and buildings. |
| What does the power station do in the national grid? | It generates electricity through coal/ oil/ gas/ nuclear energy of even the wind, providing 25,000 volts. |
| What do the high voltage transmission lines do in the national grid? | They carry the current over long distances. The power dissipated by the wires obey P = I² × R, so it's important that the resistance stays low. This is achieved by increasing the voltage. |
| What formula shows you how much the transformer will affect the potential difference? | Voltage in secondary coil/ Voltage in primary coil = Turns in secondary coil/ Turns in primary coil
E.g.
> 132,000 V/ 25,000 V = 132 Turns/ 25 Turns |
