CIE AS Level Physics: Understanding Electric Current and Charge Calculation

Electric Current

Flow of charge carriers, measured in amperes (A).

Charge Carriers

Particles that carry electric charge, positive or negative.

Conventional Current

Defined flow of positive charge from positive to negative.

Electron Flow

Movement of electrons from negative to positive terminal.

Ammeter

Device to measure electric current in amperes.

Series Connection

Ammeter must be connected in series with circuit.

Quantisation of Charge

Charge exists in discrete amounts or quanta.

Elementary Charge

Charge of a proton or electron, ±1.60 × 10⁻¹⁹ C.

Electric Charge

Measured in coulombs (C), can be positive or negative.

Charge Equation

Q = It relates charge, current, and time.

Drift Speed

Average speed of charge carriers in a conductor.

Number Density

Number of charge carriers per unit volume (m⁻³).

Cross-Sectional Area

Area through which current flows, measured in m².

Current Equation

I = Anvq relates current, area, density, and charge.

Current Measurement

Current is always a positive value in calculations.

Flow Direction

Conventional current flows opposite to electron flow.

Current in Conductors

Current results from movement of charge carriers.

Charge Flow

Charge can flow between two conductors under potential difference.

Current Calculation Example

8 mA current occurs when 4 C passes in 500 s.

Charge of Electron

Charge of electron is -1.60 × 10⁻¹⁹ C.

Charge of Proton

Charge of proton is +1.60 × 10⁻¹⁹ C.

Instantaneous Current Flow

Current appears to flow instantly due to high carrier density.

Current Carrying Conductor

Conductor's current is due to charge carrier movement.

Flow of Electrons

Electrons flow from negative terminal to positive terminal.

Potential Difference

Voltage that causes charge carriers to flow.

Charge Multiples

Charge occurs in multiples of elementary charge.