Electricity and Circuits Flashcards
What three subatomic components make up an atom?
Protons
Neutrons
Electrons
Describe the structure of an atom
Protons and neutrons in the nucleus
Electrons surrounding the nucleus in shells
How is current defined
The rate of flow of electrons around a circuit
What two ways that a component can be connected in a circuit?
Series (same loop)
Parallel (adjacent loop)
Describe series circuits
Closed circuit
Current is the same everywhere
The p.d is shared between each component.
Describe parallel circuits
Branched circuit
Current splits into multiple paths
The p.d across each component is the same on each branch.
Where must the voltmeter be placed in a circuit?
In parallel with the component that is being measured.
What two factors does the current in a circuit depend on?
Potential difference
Resistance
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.
How does resistance affect the current in a circuit?
As the total resistance of a circuit increases, the current flowing through the circuit decreases.
How can the current in a circuit be varied?
Using a variable resistor
How is total resistance affected by two resistors in a series circuit?
The total resistance increases; it is equal to the sum of two resistors.
How is total resistance affected by two resistors in a parallel circuit?
The total resistance decreases
What is an ohmic conductor?
- A conductor for which current and potential difference are directly proportional.
- Resistant remains constant whilst current changes.
- Temperature must be constant.
List four components in which resistance is not constant when current changes
- Filament lamps
- Diodes
- Thermistors
- Light dependent resistors (LDRs)
What happens to the resistance of a filament lamp as the temperature increases? Why? (3)
- Resistance increases
- Metal ions have more kinetic energy, so vibrate more, colliding more frequently with electrons as they flow through the metal.
- This creates more resistant to current flow.
What is different about current flow through a diode?
The current only flows in one direction.
Resistance is very high in other direction, preventing current flow.
State what happens to the resistance of a thermistor as temperature increases
The thermistor resistance 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 temperature is too high.
State what happens to the resistance of an LDR as light intensity decreases
The resistance increases
Give an application for LDR
Street lamps - when light levels drop at night, resistance increases and the light gains sufficient current to turn on.
How do diodes work?
A diode 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 factors affect the energy transferred when charge flows through a component?
Amount of charge
The potential difference across the component
Define potential difference
The work done per unit charge
When an electrical current flows through a resistor why does it heat up?
There are collisions between the electrons and the ions in the resistors lattice.
This causes a transfer in kinetic energy into thermal energy, which is released into the surroundings.
How do low resistance wires reduce unwanted energy transfers?
A smaller resistance means fewer collisions, therefore less energy will be wasted through heating.
Define power
The energy transferred per second/The rate of energy transfer
Give equations linking power and resistance
power = (current)^2 x resistance
power = (potential difference)^2 / resistance
What does AC mean?
Alternating current
This is current which is constantly changing between a negative and a positive maximum.
What does DC mean?
Direct current
This is current which takes a constant value.
Is mains electricity an AC or DC supply?
Mains electricity is an AC supply.
What is meant by the frequency of a supply?
This is the rate at which AC current changes.
What is the frequency and voltage of the UK mains electricity supply?
Frequency: 50Hz
Voltage: 230V
What type of current do batteries and cells supply?
Direct current
What is the power rating of an appliance?
It shows how much energy a device converts per second.
What wires does a typical appliance have?
Live wire - brown
Neutral wire - blue
Earth wire - green and yellow
Explain when earth wires 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.
What is the purpose for neutral wires?
To complete the circuit by connecting the appliance back to the mains supply.
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 flowing through the wire. This provides a method to stop current flowing through appliances.
Why is it dangerous to have a connection between earth and live wires?
It can result in a surge, causing electric shocks
