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level: Electricity

Questions and Answers List

level questions: Electricity

QuestionAnswer
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 voltmeterSomething 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 difference1. 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?9If 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