P2 - Electricity Flashcards
What is electric current?
A flow of electrical charge.
Current flows in a complete (closed) circuit only if there is a potential difference.
What is the unit of current?
Ampere, A.
What drives the flow of electric charge in a circuit?
Potential difference (or voltage).
Its unit is the volt, V.
What is the relationship between current and resistance?
The current depends on the potential difference and the resistance of the component.
What happens to the current when resistance increases?
The current decreases for a given potential difference.
How is the total charge through a circuit calculated?
Q = It, where Q is charge, I is current, and t is time.
What is the formula to calculate charge flow?
Q = It.
If a battery charger passes a current of 2.0 A over 2.5 hours, how much charge is transferred?
18,000 C.
What is the symbol for a battery in a circuit diagram?
Battery symbol.
What does a switch symbol represent in a circuit diagram?
An open or closed switch.
What is the symbol for a filament lamp in a circuit diagram?
Filament lamp symbol.
What does the fuse symbol indicate in a circuit diagram?
A fuse.
What does LED stand for in circuit diagrams?
Light Emitting Diode.
What is the symbol for a resistor in a circuit diagram?
Resistor symbol.
What is a variable resistor used for?
To adjust resistance in a circuit.
What is the purpose of a voltmeter in a circuit?
To measure potential difference (voltage).
What does a diode do?
Allows current to flow in one direction only.
Fill in the blank: The unit of resistance is _______.
Ohm, Ω.
What is an LDR?
Light Dependent Resistor.
What is the function of a thermistor?
To change resistance with temperature.
What does an ammeter measure?
Current in a circuit.
What does the formula V = IR represent?
The relationship between potential difference (V), current (I), and resistance (R)
This formula is fundamental in understanding electrical circuits.
What is the formula to calculate current (I) from potential difference (V) and resistance (R)?
I = V ÷ R
This rearrangement of V = IR allows for calculating current when V and R are known.
If a resistor has a potential difference of 6.0 V and a resistance of 4.0 Ω, what is the current?
1.5 A
Calculated using I = V ÷ R, where V = 6.0 V and R = 4.0 Ω.
To find the formula for a missing variable in V = IR, what method can you use?
Use a formula triangle
Cover up the variable you want to find; the remaining visible parts give the formula.
What is the unit of resistance in the formula V = IR?
Ohm (Ω)
Resistance is measured in ohms, which quantify how much a material opposes the flow of current.
True or False: The current through a resistor can be directly calculated if potential difference and resistance are known.
True
This is a direct application of the formula I = V ÷ R.
Fill in the blank: Potential difference (V) is equal to _______ multiplied by resistance (R).
Current (I)
This emphasizes the direct relationship between these electrical quantities.
What is the behavior of resistance in ohmic conductors?
The resistance of ohmic conductors remains constant regardless of the current
Examples of ohmic conductors include wires and resistors.
How is the current related to potential difference in an ohmic conductor?
The current is directly proportional to the potential difference across it at a constant temperature
This relationship is described by the formula V = IR.
What happens to the resistance of a filament lamp as the current increases?
The resistance increases as the filament heats up
This is due to the transfer of energy to the thermal energy store of the filament.
Describe the resistance behavior of diodes.
Diodes allow current to flow easily in one direction but have very high resistance in the reverse direction
This directional property is essential for their function in circuits.
What does the term ‘I-V characteristic’ refer to?
It refers to a graph that shows how the current flowing through a component changes as the potential difference across it is varied.
What is the I-V characteristic of linear components?
Linear components have a straight line I-V characteristic
An example is a fixed resistor.
What is the I-V characteristic of non-linear components?
Non-linear components have a curved I-V characteristic
Examples include filament lamps and diodes.
What is the first step in finding a component’s I-V characteristic?
Set up the test circuit with a variable resistor.
What should you do after varying the variable resistor in the I-V characteristic experiment?
Take several pairs of readings from the ammeter and voltmeter.
What is the purpose of swapping the wires connected to the battery in the I-V characteristic experiment?
To reverse the direction of the current.
How can you calculate resistance at any point on the I-V characteristic?
By using the formula R = V/I.
Fill in the blank: The current through an ohmic conductor is ______ to the potential difference.
directly proportional.
True or False: The I-V characteristic of an ohmic conductor is a straight line.
True.
In the context of I-V characteristics, what happens to the current flow in a diode when the direction is reversed?
The current will not flow due to very high resistance.
What does LDR stand for?
Light Dependent Resistor
An LDR is a resistor that is dependent on the intensity of light.
How does the resistance of an LDR change in bright light?
The resistance falls.
What happens to the resistance of an LDR in darkness?
The resistance is highest.
Name three applications of LDRs.
- Automatic night lights
- Outdoor lighting
- Burglar detectors
What is a thermistor?
A temperature dependent resistor.
How does the resistance of a thermistor change in hot conditions?
The resistance drops.
What happens to the resistance of a thermistor in cool conditions?
The resistance goes up.
List two examples of thermistor applications.
- Car engine temperature sensors
- Electronic thermostats
What are sensing circuits used for?
To turn on or increase the power to components depending on conditions.
What does the fixed resistor and fan have in common in a sensing circuit?
They always have the same potential difference across them.
In a sensing circuit, how is the potential difference shared?
According to their resistances.
What happens to the potential difference across the fixed resistor and the fan as the room gets hotter?
It rises, making the fan go faster.
If a bulb is connected in parallel to an LDR, what happens when it gets dark?
The potential difference across both the LDR and the bulb will be high.
Fill in the blank: The greater the pd across a component, the more _______ it gets.
energy
What effect does darkness have on the brightness of a bulb connected across an LDR?
The bulb gets brighter.
What is the main difference between series and parallel circuits?
Components in series are connected end to end; in parallel, they are connected across the same voltage supply.
Series circuits have all components in a single path, whereas parallel circuits have multiple paths for current.
What happens to the current if one component is removed from a series circuit?
The circuit is broken, and all components stop working.
This characteristic makes series circuits less practical for many applications.
How is the total potential difference (pd) in a series circuit calculated?
Total pd = V1 + V2 + …
The total potential difference is shared among all components in the circuit.
What is the relationship between current and components in a series circuit?
The same current flows through all components.
This is a defining feature of series circuits.
How do you determine the size of the current in a series circuit?
I = V ÷ R
Where V is the total potential difference and R is the total resistance.
What is the formula for calculating total resistance in a series circuit?
R_total = R1 + R2
The total resistance is simply the sum of the resistances of individual components.
What effect does adding a resistor in series have on total resistance?
Total resistance increases.
Adding a resistor reduces the total current because the potential difference is shared.
How does the resistance of a component affect its share of the total potential difference?
The bigger a component’s resistance, the bigger its share of the total potential difference.
This means higher resistance components will have a larger voltage drop across them.
If two cells with a potential difference of 1.5 V are connected in series, what is the total potential difference supplied?
3 V
This is because the potential differences add up in series.
True or False: In a series circuit, the potential difference across each component is the same.
False
The potential difference is divided among the components based on their resistances.
Fill in the blank: In a series circuit, the formula for current is I = V ÷ _____.
R
R represents the total resistance in the circuit.
What type of circuits are all the electrics in a house wired in?
Parallel circuits
Parallel circuits are more common due to their advantages in functionality.
In parallel circuits, how are components connected to the power supply?
Each component is separately connected to the +ve and -ve of the supply
Ammeters are an exception, as they are always connected in series.
What happens if one component is removed or disconnected in a parallel circuit?
It will hardly affect the others
This independence is crucial for many applications, like household electrics.
Why is it necessary for components in household electrics to be connected in parallel?
To be able to switch everything on and off separately
This allows for greater control over individual devices.
What is the relationship of potential difference across all components in a parallel circuit?
The potential difference is the same across all components
V1 = V2 = … for all components.
What can be said about the brightness of identical bulbs connected in parallel?
All will be at the same brightness
This is due to the equal potential difference across them.
How is total current defined in a parallel circuit?
Total current is equal to the total of all the currents through the separate components
Total current entering a junction equals total current leaving.
What happens to the current flow through identical components connected in parallel?
The same current will flow through each component
This is a consequence of equal potential difference.
What is the effect of adding a resistor in parallel on total resistance?
It reduces the total resistance
The total resistance is less than the resistance of the smallest resistor.
What is the ‘pushing force’ making current flow in parallel circuits?
The same as the source potential difference for each resistor
This uniformity allows for increased current flow.
Fill in the blank: In a parallel circuit, adding another loop allows the current to have _______.
more than one direction to go in
What is the relationship between current and resistance in a parallel circuit according to Ohm’s Law (V = IR)?
An increase in current means a decrease in total resistance
This is because adding paths for current flow reduces overall resistance.
What type of electricity supplies the mains in the UK?
AC supply at around 230 V
AC stands for alternating current.
What is the frequency of the UK mains supply?
50 Hz
50 Hz means 50 cycles per second.
What type of current do batteries supply?
Direct current (DC)
DC is a current that flows in the same direction.
What are the three wires in a three-core electrical cable?
- Live wire (brown)
- Neutral wire (blue)
- Earth wire (green and yellow)
Each wire has a specific function and color coding.
What is the purpose of the live wire?
Provides the alternating potential difference from the mains supply
The live wire carries the current at about 230 V.
What does the neutral wire do?
Completes the circuit and is around 0 V
Current flows through both live and neutral wires when the appliance is operating normally.
What is the function of the earth wire?
For protecting the wiring and ensuring safety
The earth wire prevents the appliance casing from becoming live.
What happens if you touch the live wire?
A large potential difference is produced across your body, causing an electric shock
This shock could injure or even kill you.
True or False: There is no danger of electric shock if a light switch is turned off.
False
Even when switched off, there is still a potential difference in the live wire.
What can happen if there is a low resistance path between live and earth?
A huge current will flow, which could result in a fire
This connection can be extremely dangerous.
Fill in the blank: Direct current is created by a _______.
direct voltage
Direct current flows in one direction.
What is the relationship between charge and work done in an electrical circuit?
Work done is the same as energy transferred to the charge.
How does a kettle transfer energy?
Kettles transfer energy electrically from the mains AC supply to the thermal energy store of the heating element.
How does a handheld fan transfer energy?
Energy is transferred from the battery to the kinetic energy store of the fan’s motor.
True or False: All electrical appliances transfer energy completely usefully.
False
What happens to energy transfer as current increases?
More energy is transferred to the thermal energy stores of the components and their surroundings.
What is the formula for calculating the energy transferred by an electrical appliance?
Energy transferred (J) = Power (W) * Time (s)
What does the power of an appliance indicate?
The energy that it transfers per second.
Calculate the energy transferred by a 600 W microwave used for 5 minutes.
180,000 J
How long would a 750 W microwave take to do the same amount of work as a 600 W microwave used for 5 minutes?
4 minutes
What does a power rating indicate for an appliance?
The maximum amount of energy transferred between stores per second when the appliance is in use.
Why is the power rating important for customers?
It helps customers choose between models based on electricity usage and running costs.
Fill in the blank: A higher power rating does not necessarily mean that an appliance transfers more energy _______.
[efficiently]
What does a lower power rating imply about an appliance’s electricity usage?
It uses less electricity in a given time, making it cheaper to run.
True or False: An appliance can be more powerful but less efficient than another.
True
What is the formula for energy transferred when an electrical charge goes through a change in potential difference?
E = QV
E represents energy transferred, Q represents charge flow, and V represents potential difference.
What happens to energy when a charge ‘falls’ through a potential drop in a circuit?
The charge gives up this energy when it ‘falls’ through any potential drop in components elsewhere in the circuit.
This energy is then converted to other forms, like kinetic or thermal energy.
How does a battery with a bigger potential difference affect energy supplied to the circuit?
A battery with a bigger pd will supply more energy to the circuit for every coulomb of charge that flows round it.
This is because the charge is raised up ‘higher’ at the start.
Calculate the energy transferred by a 3 V battery when 140 C of charge passes through the circuit.
E = 420 J
Calculation: E = QV = 140 × 3.
What is the relationship between power, potential difference, and current?
Power (W) = Potential difference (V) x Current (A)
This can also be expressed as P = VI.
If a hair dryer has a power of 1.0 kW and is connected to a 230 V supply, what is the current through the hair dryer?
4.3 A
Calculation: I = P ÷ V = 1000 ÷ 230.
What formula can be used to find power if the potential difference is unknown?
P = I²R
This results from substituting V = IR into P = VI.
Fill in the blank: The energy transferred to the motor of an electric toothbrush is converted to _______ and thermal energy stores.
kinetic energy
This energy supports the motor’s operation and contributes to heat.
True or False: A potential difference is the energy supplied to a charge at the power source.
True
The potential difference is what allows the charge to gain energy.
What does an increase in potential difference imply about the energy supplied to the circuit?
It implies that more energy is supplied for each coulomb of charge that flows.
Higher potential difference results in greater energy elevation for the charges.
What is the National Grid?
A web of wires covering Britain that connects power stations to homes and consumers.
The National Grid is responsible for distributing electricity from power stations to users across the UK.
How does the National Grid transfer electricity?
It transfers electrical power from power stations (supply) to consumers (demand) across the grid.
Consumers can include homes and industries that use electricity.
What must electricity production meet?
The demand for electricity at all times.
Demand varies throughout the day based on factors such as time of day and special events.
When does electricity demand typically increase?
In the morning, after school or work, and when it gets dark or cold.
Events like major sporting finals can also cause peaks in electricity demand.
How do power stations manage unexpected high demand?
They often operate below maximum output and keep smaller power stations on standby.
This ensures there is spare capacity available in case of sudden demand spikes.
What is necessary for efficient power transmission in the National Grid?
A high potential difference and a low current.
This is because high current leads to significant energy loss as heat in the wires.
What is the maximum potential difference used in the National Grid?
400,000 V.
This high voltage allows for efficient energy transfer over long distances.
What happens to energy loss when potential difference is increased?
Energy loss decreases as current decreases.
Higher potential difference allows for lower current, which minimizes energy loss as heat.
What role do transformers play in the National Grid?
They change the potential difference for efficient power transmission.
Transformers consist of two coils and an iron core, and can either step up or step down voltage.
What is a step-up transformer?
A transformer that increases potential difference by having more turns on the secondary coil than the primary coil.
This process decreases the current as the potential difference increases.
What is a step-down transformer?
A transformer that decreases potential difference and increases current.
It has more turns on the primary coil than the secondary coil.
What is the relationship between power, potential difference, and current in transformers?
Power in the primary coil equals power in the secondary coil (VI = VI).
This means transformers are nearly 100% efficient.
