Lesson summary
9.1.1 Electric Current — AS PHYSICS 9702 notes: Define electric current, conventional current and quantisation of charge.Definition — electric current is the flow of charge carriers, measured in amperes (A).Carriers — charge carriers can be positive or negative.Cause — when a con…
- Direction rule
- Connection
- Elementary charge
- Drift speed
- Cause — when a conductor is exposed to a potential difference, charge carriers flow
- Ammeter — the instrument that measures current
Section 1 of 7Defining electric current
Definition
- Definition electric current is the flow of charge carriers, measured in amperes (A).
Carriers
- Carriers charge carriers can be positive or negative.
Cause
- Cause when a conductor is exposed to a potential difference, charge carriers flow.
Section 2 of 7Conventional current and electron flow
1Electrons
- Electrons in electrical wires the current is a flow of electrons, which are negatively charged.
- They flow away from the negative terminal of a cell towards the positive terminal.
2Conventional current
- Conventional current the flow of positive charge from the positive terminal to the negative terminal.
- It is opposite to electron flow, because it was described before the electron was discovered.
3Direction rule
- Direction rule by definition, conventional current always goes from positive to negative.
Section 3 of 7Measuring current
Ammeter
- Ammeter the instrument that measures current.
Connection
- Connection it must be connected in series so that the charged particles flow through it.
Section 4 of 7Quantisation of charge
Quanta
- Quanta charge is carried in discrete amounts, sometimes called packets.
Electron
- Electron its charge is −1.60 × 10−19 C.
Proton
- Proton its charge is +1.60 × 10−19 C.
Elementary charge
- Elementary charge this value is called the elementary charge, e.
Multiples
- Multiples charge always occurs in whole-number multiples of the elementary charge.
Section 5 of 7More from the specification
Density
- Mass per unit volume.
Coulomb
- Charge passing a point when a current of 1 A flows for 1 s.
Drift speed
- Drift speed the average speed of charge carriers along a conductor;
- it is very small and is linked to current by I = nAvq.
Section 6 of 7Key terms
| Term | Meaning |
|---|---|
| Electric current | Flow of charge carriers, measured in amperes. |
| Conventional current | Flow of positive charge from the positive to the negative terminal. |
| Ammeter | Instrument connected in series to measure current. |
| Elementary charge | Magnitude of the charge of a proton or electron, 1.60 × 10⁻¹⁹ C. |
| Quantised | Occurring only in discrete multiples of a basic amount. |
Section 7 of 7Exam technique
1
Saying current flows from negative to positive — conventional current flows from positive to negative.
2
Connecting an ammeter in parallel — it must be in series.
3
Thinking charge can take any value — it is quantised.
4
Giving a negative value for current in answers — conventional current is positive.