Basics
SI Prefixes
The most common ones you'll see in this course are:
- Mega (M)
- Kilo (k)
- Mili (m)
- Micro ()
- Nano (n)
- Pico (p)
Charge
The unit of charge is Columbs (C), which is equal to charge of electrons.
Charges cannot be created or destroyed, they are just transferred.
Current
Current is the rate of charge flow (). 1 A equals to 1 Coulomb/seconds.
Video: Current and Amps: What are they?
Voltage
Voltage is related to the strenght of the electric field. It is analogous to pressure in a hydraulic circuit.
! Voltage is always measured between two points, that is why it is also called potential difference.
Voltage is equal to rate of work done by unit charge.
Video:Voltage/Volts: What is it?
Analogy to Hydraulic System
- Voltage ~ Pressure
- Electric Current ~ Water Current
- Tap Resistance ~ Resistance
Power
Power is the rate of energy (expending or absorbing), denoted by :
In electric circuits power is equal to multiplication of voltage and current.
The unit of power is Watt.
Energy
Energy in the time integral of power. The unit of energy is Joules, which is equal to watt.seconds.
It is also common practice to express electrical energy in kilo-watt hours (kWh).
Example: Electricity bills(photo1, photo2) are calculated in terms of kWh.
Absorbing or Dissipating?
Circuit Symbols
Resistance
Limits the electric current. The unit is Ohm ()
Voltage Source
An ideal voltage source produces a voltage regardless of the current absorbed or produced by the device. Can be a battery, DC voltage source or AC voltage source.
A lemon battery is also a DC voltage source (not an ideal one)
Current Sources
An ideal current source produces the specified current regardless of the voltage across its terminals.
