Topic 10 - Circuits Flashcards
What does AC mean?
Alternating current
What does DC mean?
Direct current
Is mains electricity AC or DC?
AC
What is meant by the frequency of a supply?
The rate at which an AC current changes
What is the frequency and voltage of the UK mains electricity supple?
Frequency = 50Hz Voltage = 230V
What type of current do batteries and cells supply?
Direct current (DC
What is the power rating of an appliance?
It shows how much energy a device converts per second
What wires does a typical domestic appliance have?
Live wire
Neutral wire
Earth wire
What colour is the live wire?
Brown
What colour is the neutral wire?
Blue
What colour is the earth wire?
Green and yellow (striped)
Explain when the earth wire does and doesn’t carry a current
Under normal circumstances, no current flows through the earth wire
Current flows when a fault occurs in the appliance (such as a surge or the casing becoming live)
What potential is the neutral wire at?
0 volts
State the potential difference between the live and earth wires
230 volts
What is the purpose of the neutral wire?
The complete the circuit by connecting the appliance back to the mains supply
For metal appliances, where is the the earth wire connected to? Why?
The metal casing of the appliance
If the live wire becomes touching the casing, the current will flow through the earth wire, preventing electrocution
How does a fuse stop a device from getting damaged?
When the current becomes too high the fuse wire will melt and break, therefore stopping current from flowing to the appliance and preventing damage
Why is it important to connect a fuse or switch to the live wire?
When the switch is turned off, or when the fuse breaks, it will break the circuit and stop current running through the wire. This provides a method to stop current flowing into the appliance
Why is it dangerous to have a connection between the earth wire and the live wire?
It can result in a current surge, causing electrical shocks
What factors affect the energy transferred when charge flows through a component?
Amount of charge
The potential difference across the component
How do you work out energy?
Current x potential difference x time
Define potential difference in terms of charge
The work done per unit charge
How to work out energy transferred
Charge x potential difference
When an electrical current flows through a resistor why does it heat up?
There are collisions between the electrons and the ions in the resistor’s lattice. This causes a transfer of kinetic energy into thermal energy which is released into the surroundings
How do low resistance wires reduce unwanted energy transfers?
A smaller resistance will mean there are fewer collisions, therefore less energy will be wasted through heating
What are some advantages of the heating effect in resistors?
It is useful for appliances such as toasters or electrical fires, where the heat is the desired product
What are some disadvantages of the heating effect in resistors?
The loss of energy as it can make an appliance inefficient
If an appliance overheats it can catch fire or overhear, which could ruin the device or injure the user
What are the units of power?
Watts (W)
Define power
The rate of energy transfer or the rate at which work is done
How do you work out power (in circuit)?
Current x potential difference OR Current^2 x resistance OR Energy/time
How does resistance affect current in a circuit?
As the total resistance of a circuit increases, the current flowing through the circuit decreases
How can’t he current in a circuit be varied?
Using a variable resistor
How do you calculate potential difference?
Current x resistance
Energy transferred/charge
How is total resistance affected by two resistors in series?
The total resistance is equal to the sum of the two resistors
How is total resistance affected by two resistors in parallel?
The total resistance decreases; it is less than the resistance of the resistor with the lowest resistance
What is an ohmic conductor ? State the condition required
A conductor for which current and potential difference are directly proportional
Resistance remains constant as current changes
Temperature must be constant
List 4 components for which resistance is not constant as current changes
Filament lamps
Diodes
Thermistors
Light dependant resistors
What happens to the resistance of a filament lamp as the temperature increases? Why?
Resistance increases
Metal ions have more kinetic energy so vibrate more, colliding more frequently with electrons as they flow through the metal
This created more resistance to current flow
What is different about current flow through a diode?
The current only flows in one direction
Resistance is very high in the other direction, preventing current flow
State what happens to the resistor of a thermistor as temperature increases?
It decreases
Give two examples of when a thermistor may be used
In a thermostat to turn a heater on below a certain temperature
In a freezer to turn on a cooler when the temperature becomes too high
State what happens to the resistance of an LDR as light intensity decreases
It increases
Give an application for a LDR
Street lamps or night lights
How do diodes work?
It only allows current to flow in one direction. If current is flowing the right way, the resistance is large for small voltages, but then at higher voltages becomes very small
What are the two ways that a component can be connected in a circuit?
Series or parallel
What is voltage also know as?
Potential difference
How does the potential difference across two components vary when connected in series and parallel?
In a series circuit the total potential difference is shared between each component
In a parallel circuit the potential difference across each component is the same
If two resistors are connected in parallel, what can be said about their combined total resistance?
Their total resistance is less than the smallest of the two individual resistances
If two resistors are connected in series what can be said about their total resistance?
Their total combined resistance is equal to the sum of the two individual resistances
Where must a voltmeter be placed in a circuit?
In parallel with the component that is being measured
How can a volt be described?
Joule per coulomb
What is an electric current?
The rate of flow of charge
How to work out charge
Current x time
What can be said about the value of current at any point in a single closed loop?
Current is the same in all points in a closed loop
What two factors does the current in a circuit depend on?
Potential difference
Resistance
What is an ammeter and where must it be connected in a circuit?
An ammeter measures current . It is placed in series with the component it is required to measure
What happens when current reaches a junction in a circuit?
Current is conserved; the total current remains the same and is split between the two branches
What three subatomic components make up an atom?
Electrons
Protons
Neutrons
How is current defined?
The rate of flow of charge (or electrons) around a circuit
What are the units of charge?
Coulombs (C)
