Voltage and Current

MEE1008: Dynamic Systems 1 - Lecture 1

Voltage

The difference in electric potential energy between two points per unit electric charge.

Other names for voltage

Electric potential difference, electric pressure or electric tension.

Voltage symbols

V or U.

The voltage between two points is equal to

the work done per unit
of charge against a static electric field to move the test charge between two points.

Voltage unit

Volts (a joule per coulomb).

How a battery works

The applied voltage is the starting mechanism - the current is a reaction to the applied voltage.

Conventional current

The direction of positive charge. (This is not how current actually flows)

Electric current formula

I = Q/t

The rate of flow of electric charge

I = dQ/dt

Unit of current

Ampere / amp (A)

Resistance

The opposition to the flow of charge through an electrical circuit.

Resistance units

Ohm (Ω)

Resistance symbol

Omega (Ω)

Factors that affect resistance

Material, length, cross-sectional area, temperature of the material.

Factors that increase resistance

A long path through which the free electron must pass, a small cross sectional area, low temperature.