1.1: Definitions

ELECTRICAL CIRCUIT: Interconnection of electrical elements and symbols. They divide into:

a) Passive: Cannot generate energy

• Resistor (R) - [Ohms]
• Capacitor (C) - [Farads]
• Inductor (L) - [Henries]

b) Active: May or may not generate/supply energy

• Voltage (V) - [Volts]
• Current (I) - [Amps]

Important definitions in circuits go as follows:

RESISTANCE:
Resist flow of current.

CURRENT:

It is the movement or flow of charge (1.602x10^-19 Coulombs) in a circuit.

Current is derived as:

i (t) = dq/dt (amps)

VOLTAGE:

Energy required to move a unit of charge through an element.

Voltage is derived as:

V = dw/dq (volts)

POWER:

Time rate of expanding or absorbing energy.

Power is derived as:

P = dw/dt or current (I) x voltage (V) (watts)

• Absorbed power: when current enters a positive terminal.
• Supplied power: when current enters a negative terminal.

Example:
Determine the amount of power absorbed or supplied if:
1) Voltage = 8V and Current =-3A
-> Power = VxI = 8V x -3A = -24W supplied

ENERGY:

Power derived from the utilization of physical resources.

Energy is derived as

Integration [ Pdt]

CONSERVATION:

a) Charge is not created or destroyed only transformed.

b) Total energy or power supply to a circuit must equal total energy/power absorbed.