Topic 5 -Electricity and Circuits Flashcards
What is current?
The flow of electric charge - the rate of flow of charge
When is the only time a current will flow through an electrical component?
If there is a potential difference across the component and if the circuit is complete
What is the unit for current?
Ampere (A)
What is potential difference?
- The same as voltage
- the driving force that pushes the charge around the circuit
- the energy transferred per coulomb of charge that passes between two points in an electrical circuitry
What is the unit for voltage/potential difference?
Volt (V)
What is resistance?
Anything that slows the flow of the charge down
What is the unit for resistance?
Ohms (Ω)
How does the potential difference affect the current?
The higher the potential difference across a given component, the higher the current will be
How does resistance affect the current?
The greater the resistance of a component, the smaller the current
In metals what is current caused by?
The flow of electrons
What is the symbol for current?
I
What is the equation relating charge, current and time?
Charge = current x time
Q
I t
When does more charge pass around a circuit in a given time?
When a greater current flows
What is charge measured in?
Coulombs (C)
SYMBOL CARDS USING WEBSITE
SYMBOL CARDS USING WEBSITE
How can you calculate energy transferred from charge and potential difference?
Energy transferred = charge moved x potential difference
E = Q x V
What is energy measured in?
Joules
What is the potential difference across an electrical component?
The amount of energy transferred by that electrical component per unit of charge passed
What is one volt equal to?
One joule per coulomb
How can you calculate voltage from current and resistance?
Potential difference = current x resistance
V = I x R
When an electrical charge flows through a component what does it have to do?
Do work against resistance
What does work done against resistance cause?
An electrical transfer of energy
What is work done equal to?
Energy transferred
When a current flows through a resistor what happens? Why?
- The resistor heats up
- Because some of the energy transferred is dissipated to the thermal energy stores of the component and the surroundings - not all of the energy from work done against resistance is transferred usefully
How is energy transferred to the thermal energy stores of a component and the surroundings?
The electrons collide with the ions as they flow through the lattice which makes up the resistor.
Why does the current decrease as a resistor heats up if there is a given p.d.?
The more the ions vibrate, the more difficult it is for electrons to get through the resistor because there are more collisions
What does p.d. stand for?
Potential difference
What happens if a resistor gets too hot?
No current will be able to flow (apart from with thermistors)
What happens to the resistance or a thermistor with an increase in temperature?
It decreases
What do low resistance wires do to the energy dissipated to thermal energy stores when current flows between components?
Decrease the energy dissipated
What circuit can you use to investigate the relationship between current, p.d. and resistance for a range of components?
A parallel circuit with a variable d.c. source of power with an ammeter in series and a voltmeter in parallel around any resistor
What components can you investigate in a circuit to investigate the relationship between current, p.d. and resistance?
A filament bulb or a fixed resistor
What does an ammeter measure?
The current flowing though a component in amps
Where should an ammeter be placed in a circuit?
Anywhere in the main circuit but it must be in series, NEVER IN PARALLEL
What does a voltmeter measure?
The potential difference across a component
Where must a voltmeter be placed in a circuit?
In parallel with the component under test
