P2 Ai Flashcards
What is the purpose of understanding circuit diagrams?
To be able to understand and draw them using the correct symbols.
What symbol represents an open switch in a circuit diagram?
Switch open
What is the symbol for a battery in circuit diagrams?
Battery
What are the components in a circuit?
Parts like bulbs, resistors, etc.
What does the potential difference in an electrical circuit represent?
The ‘driving force’ that pushes charge around the circuit.
What is the unit of electric current?
Amperes, A
What is the unit of electrical charge?
Coulombs, C
What is required for electrical charge to flow in a circuit?
A complete (closed) circuit and a potential difference.
What is resistance in the context of electric circuits?
Anything that slows down the flow of charge.
In a single, closed loop circuit, how does the current behave?
The current is the same everywhere in the circuit.
What is the relationship between charge flow, current, and time?
Charge flow (C) = Current (A) x Time (s) or Q = It.
What is the formula for Ohm’s Law?
V = IR
What is sometimes referred to as ‘voltage’?
Potential difference
If a battery charger passes a current of 2 A for 300 seconds, how much charge is transferred?
600 C
True or False: A closed circuit allows electrical charge to flow.
True
Fill in the blank: Electrical current is a flow of _______.
electrical charge
What is the symbol for a filament lamp in circuit diagrams?
Filament lamp (or bulb)
What is the symbol for a diode in circuit diagrams?
Diode
What is the symbol for an LED in circuit diagrams?
LED
What should you ensure about the wires in a circuit diagram?
All wires should be straight lines.
What is the significance of a closed circuit?
Allows continuous flow of current.
What is the formula that links potential difference, current, and resistance?
V = IR
V is potential difference in volts (V), I is current in amps (A), and R is resistance in ohms (Ω)
What does resistance measure?
How much the current is slowed down
Greater resistance results in smaller current for a given potential difference
What happens to current if the resistance across a component increases?
The current decreases
This is true for a given potential difference across the component
Fill in the blank: The formula linking potential difference (pd) and current is: V = _____
IR
What is the current through a 4.0 Ω resistor with a potential difference of 6.0 V across it?
1.5 A
Calculated using the formula I = V ÷ R
What are ohmic conductors?
Components with a fixed resistance
Their resistance does not change with current as long as the temperature remains constant
What happens to the current in an ohmic conductor if the potential difference doubles?
The current also doubles
Current is directly proportional to potential difference in ohmic conductors
What happens to the resistance of a filament lamp as the current increases?
Resistance increases with temperature
The filament heats up and glows brighter as current increases
How does a diode behave regarding current flow?
Allows current to flow in one direction only
It has very high resistance in the opposite direction
True or False: The resistance of some components remains constant regardless of the current.
False
Components like filament lamps and diodes have changing resistance with current
What is the potential difference across an appliance if the resistance is 46 Ω and the current is 5.0 A?
230 V
Calculated using the formula V = IR
What factors can affect the resistance of a circuit?
The resistance of a circuit can depend on:
* If components are in series or parallel
* The length of wire used in the circuit
For more information on series and parallel components, see p.185.
What equipment is needed to investigate the effect of wire length on resistance?
You will need:
* Switch
* Battery
* Ammeter
* Metre ruler
* Crocodile clips
* Thin test wire
These components are typically used in simple circuit experiments.
How can you measure the resistance of a wire in an experiment?
Measure the current and potential difference (pd) across the wire using:
* A crocodile clip at 0 cm
* A second crocodile clip at a short distance
* Record the length, current, and pd
* Calculate resistance using R = V ÷ I
This formula is derived from Ohm’s Law (V = IR).
What does a graph of resistance against wire length show?
The graph should:
* Have a straight line through the origin
* Show that resistance is directly proportional to length
This indicates that the longer the wire, the greater the resistance.
True or False: Opening the switch between readings can help reduce error in measurements.
True
This allows the circuit to cool down, minimizing potential errors.
Fill in the blank: The longer the wire, the _______.
greater the resistance.
What is the equation used to calculate resistance in a circuit?
R = V ÷ I
This equation is based on Ohm’s Law.
What is the role of a variable resistor in the circuit diagram for investigating resistance?
It represents the test wire used in the investigation
Variable resistors allow for adjustments in resistance during experiments.
What is the first step in measuring the resistance of a wire in the experiment?
Attach a crocodile clip to the wire level with 0 cm on the ruler.
How should you plot your results after measuring resistance against wire length?
Plot a graph of resistance against wire length and draw a line of best fit.
What happens to the current when the wire length increases?
The current decreases as resistance increases.
What does the I-V characteristic show?
How current (I) changes with potential difference (V) across a component
What are linear components in I-V characteristics?
Components with straight line characteristics, such as a fixed resistor
How is resistance (R) calculated from I-V characteristics?
R = V ÷ I (from V = IR)
What types of components should be investigated for I-V characteristics?
- Filament lamp
- Diode
- Resistor at a fixed temperature
What type of current is used in the I-V characteristic experiments?
Direct current (dc)
What is the purpose of the variable resistor in the experiment?
To change the current in the circuit
What measurements are taken during the I-V characteristic experiment?
- Current through the component
- Potential difference across the component
What happens when the wires connected to the battery are swapped?
The ammeter displays negative readings
What is plotted on the graph in I-V characteristic experiments?
Current on the y-axis and potential difference on the x-axis
What is the shape of the I-V characteristic for a fixed resistor?
A straight line, indicating current is directly proportional to potential difference
What happens to the resistance of a filament lamp as current increases?
Resistance increases, making it harder for current to flow
What is the I-V characteristic of a diode?
Current only flows in one direction with very high resistance in the reverse direction
True or False: The filament lamp I-V characteristic shows that current is directly proportional to potential difference.
False (it shows that resistance increases with temperature, making it non-linear)
Fill in the blank: The resistance of a filament lamp ______ increases as the current increases.
resistance
What should be done with the graphs of I-V characteristics?
Draw out those graphs until you’re sketching them in your sleep
What does LDR stand for?
Light Dependent Resistor
How does the resistance of an LDR change with light intensity?
The resistance decreases in bright light and increases in darkness
What are some common uses 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 with temperature?
Resistance drops in hot conditions and increases in cool conditions
Where are thermistors commonly used?
Car engines, central heating thermostats
What is the role of thermostats in relation to thermistors?
They turn the heating on when it’s cool and off when it’s warm
What is a sensing circuit?
A circuit that automatically changes the potential difference across components based on environmental changes
How does a sensing circuit control a fan in a room?
The potential difference across the fan increases as the room gets hotter due to the thermistor’s resistance decreasing
What happens to the potential difference across a fixed resistor in a sensing circuit as the room heats up?
The potential difference across the fixed resistor rises
True or False: In a series circuit, if you remove one component, all components stop working.
True
What is the relationship between total resistance in a series circuit and the individual resistances?
Total resistance is the sum of individual resistances
What happens to the potential difference in a series circuit when additional components are added?
The potential difference is shared among the components
Fill in the blank: The bigger a component’s resistance, the _______ of the potential difference it takes.
more
How does the arrangement of LDRs and thermistors affect circuit behavior?
They can be used to create circuits that respond to changes in light and temperature
What is the effect on a fan if it is connected across a thermistor in a circuit as the room gets hotter?
The fan would slow down
What is the definition of potential difference?
The difference in electric potential energy per unit charge between two points
What is the configuration of components in a series circuit?
All components are connected in a line between the ends of the power supply.
What happens when one component is removed in a series circuit?
The circuit is broken and all components stop working.
In series circuits, how is the total potential difference (pd) of the supply distributed?
The total pd is shared between all of the components.
How do you calculate the total resistance in a series circuit?
By adding the resistances of the individual components.
Fill in the blank: In series circuits, the same ______ flows through all components.
current
True or False: In series circuits, the potential difference across each component is equal.
False
What effect does adding a resistor in series have on the total resistance of the circuit?
It increases the total resistance.
What is the relationship between a component’s resistance and its share of the total pd in a series circuit?
The bigger a component’s resistance, the bigger its share of the total pd.
If cells are connected in series, what happens to their potential differences?
Their potential differences add together to make the total pd across the circuit.
Calculate the total resistance for resistors of 2Ω and 3Ω connected in series.
5Ω
What is the formula to calculate current in a circuit?
I = V ÷ R
In a circuit with a 20V supply and a total resistance of 5Ω, what is the current?
4A
Describe the effect of adding resistors in series on the current through each resistor.
The current through each resistor is lower because they share the total pd.
What is the potential difference of a battery connected in series with a 4Ω, 5Ω, and 6Ω resistor when a current of 0.6A flows through the circuit?
Calculate using V = IR: V = 0.6 * (4 + 5 + 6) = 0.6 * 15 = 9V
What is the main characteristic of components in parallel circuits?
Every component is connected separately to the ends of the power supply.
True or False: In parallel circuits, if one loop is removed, other loops are affected.
False
What happens to the potential difference across components in parallel circuits?
The potential difference is the same across all components.
What is the relationship between the total current and the currents through individual components in parallel circuits?
The total current is equal to the sum of all the currents through the separate components.
Fill in the blank: At junctions in a parallel circuit, the total current going into a junction must equal the total current _______.
leaving it.
What is the effect of adding a resistor in parallel on the total resistance?
The total resistance is less than the resistance of the smallest of the two resistors.
How does adding another loop in a parallel circuit affect current flow?
More current can flow around the circuit, increasing the total current.
What is the formula that relates resistance, voltage, and current?
R = V/I
In a parallel circuit with identical resistors, what can be said about their brightness?
All bulbs will be at the same brightness.
What is the total current if the current into a junction is 2 A and out is 1 A + A?
1 A
What happens to the total current and resistance when one resistor is removed from a parallel circuit containing three resistors?
The total current decreases and the total resistance increases.
What is the first step in setting up a basic circuit?
Find at least four identical resistors.
What does ‘pd’ stand for in the context of a circuit?
Potential difference
How do you calculate the resistance of the circuit?
R = V ÷ I
In a series circuit, what happens to the total resistance when additional resistors are added?
Increases
In a parallel circuit, what happens to the overall resistance when additional resistors are added?
Decreases
What remains constant when adding resistors in parallel?
The pd is the same as before.
Fill in the blank: Adding resistors in ______ increases the total resistance of the circuit.
series
Fill in the blank: The more resistors you add in ______, the smaller the overall resistance becomes.
parallel
What should you plot on the graph to compare results?
Number of resistors in the circuit against the total resistance
True or False: The total current through the circuit is measured after adding resistors in series.
False
What equipment is recommended to use for a fair test when investigating circuits?
The same equipment
What type of graph is expected when plotting the total resistance against the number of resistors in parallel?
A downward sloping graph
What type of graph is expected when plotting the total resistance against the number of resistors in series?
An upward sloping graph
What is the significance of measuring current in the circuit?
It allows for the calculation of resistance.
What is the purpose of the practical experiment described?
To practice building circuits from diagrams.
What is an alternating potential difference?
A potential difference that is constantly changing direction.
Alternating current (AC) is produced by this type of potential difference.
What is the UK mains supply voltage?
Around 230 V.
This is the electricity supply in homes.
What is the frequency of the AC mains supply in the UK?
50 Hz.
Hertz (Hz) is the unit of frequency.
What is direct current (DC)?
A current that is always flowing in the same direction.
It is created by a direct potential difference.
What type of current do cells and batteries supply?
Direct current (DC).
What are the three wires in a typical three-core electrical cable?
- Live wire (brown)
- Neutral wire (blue)
- Earth wire (green and yellow)
These wires are covered with plastic insulation.
What is the function of the live wire?
Provides the alternating potential difference from the mains supply.
It is at about 230 V.
What is the function of the neutral wire?
Completes the circuit.
When the appliance is operating normally, current flows through the live and neutral wires. It is around 0 V.
What is the function of the earth wire?
Acts as a safety wire to prevent electric shocks.
It is connected to the metal casing of an appliance and helps to divert current in case of a fault.
What happens if the live wire touches the casing of an appliance?
Current flows away through the earth wire.
This helps to prevent electric shock.
What is the potential difference of the earth wire?
Around 0 V.
What can touching the live wire cause?
A dangerous electric shock.
This can happen even if the switch is turned off.
True or False: The potential difference between the live wire and your body is 0 V.
False.
Your body is at 0 V, while the live wire has a potential difference of 230 V.
What risks are associated with any connection between live and earth wires?
It could cause a huge current to flow, resulting in a fire.
Fill in the blank: The ______ wire is at about 230 V.
Live
Fill in the blank: The ______ wire is around 0 V.
Neutral
Fill in the blank: The ______ wire prevents the appliance from becoming live.
Earth
What happens whenever work is done in terms of energy?
Energy is transferred.
What is done when a charge moves around a circuit?
Work is done against the resistance of the circuit.
How is energy transferred when work is done by a charge?
Energy is transferred electrically.
What do electrical appliances transfer to components in the circuit?
Energy.
How do kettles transfer energy?
Electrically from the mains supply to the thermal energy store of the heating element.
How is energy transferred from a battery to a handheld fan?
From the battery to the kinetic energy store of the fan’s motor.
What is the relationship between power and energy transferred by an appliance?
The total energy transferred depends on how long the appliance is on for and its power.
Define power in the context of electrical appliances.
The energy that it transfers per second.
What is the equation for energy transferred by electrical work?
Energy transferred (J) = Power (W) X Time (s)
E = Pt
If a 600 W microwave is used for 5 minutes, how much energy does it transfer?
180,000 J.
How do you convert 5 minutes into seconds?
t = 5 × 60 = 300 s.
What does the power rating of an appliance indicate?
How much energy is transferred between stores when the appliance is used.
True or False: An appliance with a higher power rating will cost less to run for a given time.
False.
How much energy does a 250 W TV transfer in 2 hours?
Calculate the energy using E = Pt with t = 7200 s.
How much energy does a 375 W TV transfer in 2 hours?
Calculate the energy using E = Pt with t = 7200 s.
Calculate the power if an appliance transfers 6000 J of energy in 30 seconds.
Power = E / t = 6000 J / 30 s.
What is the significance of an appliance’s power rating?
It indicates the rate at which energy is transferred.
What is the formula for calculating energy transferred?
E = QV
Where E is energy transferred, Q is charge flow, and V is potential difference.
In the example of an electric toothbrush, how much energy is transferred with a 3.0 V battery and 140 C of charge?
420 J
Calculated using E = QV = 140 × 3.0.
What is the formula for calculating power in terms of potential difference and current?
P = VI
Where P is power, V is potential difference, and I is current.
How can power be calculated if the potential difference is not known?
P = I²R
Where R is resistance.
If a motor has a power of 1250 W and a resistance of 50 Ω, what is the current flowing through it?
25 A
Calculated using P = I²R, rearranged to I = √(P/R).
What is the current flowing through an appliance connected to a 12 V source with a current of 4.0 A?
4.0 A
This is given directly in the problem.
If an appliance has a power of 2300 W and a current of 10.0 A, what is the resistance of the appliance?
230 Ω
Calculated using P = I²R, rearranged to R = P/I².
True or False: The power of an appliance is the energy transferred in a given time.
True
Power is defined as energy transferred per unit time.
Fill in the blank: Power also depends on current and _______.
Potential Difference
Power is calculated using both current and potential difference.
What is the unit of power?
Watt (W)
Power is measured in watts.
What does the symbol ‘R’ represent in the power equations?
Resistance
Resistance is measured in ohms (Ω).
What is the relationship between energy transferred, charge, and potential difference?
Energy transferred is proportional to the product of charge and potential difference
E = QV shows this relationship.
What is the national grid?
A giant system of cables and transformers that covers the UK
It transfers electrical power from power stations to consumers.
What does the national grid do?
Transfers electrical power from power stations to consumers across the UK
Consumers refer to anyone who is using electricity.
What must electricity production do to meet demand?
Produce enough electricity for everyone to have it when they need it
The amount of electricity used changes throughout the day.
How do power stations manage fluctuations in electricity demand?
They often run at well below their maximum power output
This allows them to increase power if needed.
What is the formula for calculating power in the context of electricity?
P = VI
Where P is power, V is potential difference, and I is current.
Why does the national grid use a high potential difference?
To reduce energy lost as thermal energy stores
A high current causes more energy loss due to heating of wires.
What type of transformers are used to increase potential difference in the national grid?
Step-up transformers
They increase the potential difference from power stations to electric cables.
What type of transformers are used to decrease potential difference before electricity reaches homes?
Step-down transformers
They bring the potential difference back down to safe levels.
True or False: The national grid transfers electricity at a low potential difference to minimize energy loss.
False
The national grid transmits electricity at a very high potential difference.
Fill in the blank: The national grid can cope with high demand even if another station shuts down without _______.
[warning]
