Topic 2 - Electricity Flashcards
(13 cards)
What is current?
- electric current is a flow of electrical charge
- electric charge will only flow around a complete circuit if there is a potential difference
- the unit of current is the ampere or amps (A)
What is potential difference?
- the energy transferred per unit of charge between two points in a circuit
- it is the driving force that pushes the charge around
What is resistance?
- the opposition a component offers to the flow of electric current
- its unit is ohms
How does current, voltage and resistance link?
The greater the resistance across a component - smaller the current that flows for a given potential difference across the component
What formula links charge, current and time?
Q = IT (Charge = current x time)
What does total charge in a circuit depend on?
- depends on current and time
- the size of the current is the rate of flow of charge
- more charge passes around the circuit when a larger current flows
What formula links potential difference, current and resistance?
V = IR (Potential difference = current x resistance)
Ammeter function?
- measures the current in amps flowing through the test wire
- must always be placed in series
Voltmeter function?
- measures the PD across the test wire
- must always be placed in parallel and only around what you are investigating
6 mark metod resistance and wire investigation?
- Attach a crocodile clip to the wire level with 0cm on the ruler
- Attach the second crocodile clip to the wire, e.g. 10 cm away from the first clip. Write down the length of the wire between the clips
- Close the switch, then record the current through the wire and the pd across it
- Open the switch, then move the second crocodile clip, e.g. another 10 cm along the wire. Close the switch again, then record the new length, current and pd
- Repeat this for a number of different lengths of the test wire
- Use measurements of current and pd to calculate the resistance for each length of wire using R = V/I
- Plot a graph of resistance against wire length
What is an ohmic conductor?
a material or device that follows Ohm’s Law - current flowing through it directly proportional to voltage applied across it - as long as temperature and other physical conditions remain constant
Describe ohmic conductors?
- resistance of ohmic conductors doesnt change with the current
- at a constant temperature - current flowing through ohmic conductor is directly proportional to potential difference across it
IV characteristic
- vary variable resistor - alters current flowing through circuit and potential difference across component
- take several pairs of readings from ammeter and voltmeter - see how P.D across component varies as current changes - repeated each reading twice more to get an average
- swap over wires connecnted to battery so direction of current is reversed
- plot a graph
