ECE 140 - Linear Circuits - Chapter 1

Voltage Current and Resistance §

• Voltage (Volts) - How hard is electricity pushing (Analogous to water pressure)
• Current (Amps) - How much per second is flowing (Analogous to flow rate)
• Resistance (Ohms) - How hard do you need to push for charge to flow (How restrictive a pipe is)

1.2 - SI Units & 1.4 - Voltage & Current §

• Amount of charge (Q in Coulombs)
  • $1C=6.242\ast 10^{18}$ charges
• Electric Current (I in amps) is the charge flow rate
  • $1A=1\frac{C}{S}$
• Electric Potential (V in Volts)A is additional energy per unit of charge
  • $1V=1\frac{J}{C}$
• Electric Power (P in watts) is how much energy per charge (Volts) you put onto how much charge per second (Amps)
  • $P=V\ast I$
  • $W=1[\frac{J}{C}]\ast [\frac{C}{S}]=1[\frac{J}{S}]$
    • [] Represents Units

Important unit prefixes (for ECE 140) §

• $G=Giga=10^9$

• $M=Mega=10^6$

• $k=Kilo=10^3$

• $m=Milli=10^{-3}$

• $\mu =Micro=10^{-6}$

• $n=Nano=10^{-9}$

• $p=Pico=10^{-12}$

• Engineering Notation - Like scientific notation but snaps powers to multiples of 3

  • Eg: $0.0000421\to 42.1\ast 10^{-6}A\to 42.1\mu A$

When uncertain about # of sig figs stick to 4 (this is ONLY when no context is given)

1.5 - Ideal Circuit §

1.6 - Power and Energy §

Power = Voltage x Current

• $P=V\ast I$
• $P(t)=V(t)\ast I(t)$

Absorbing or Delivering power:

• Leaves with less energy = Absorbing
• Leaves with more energy = Delivering

Practice Problem §

Background - AC & DC §

• Direct Current (DC)
  • Current & Applied Voltage do not change direction but may fluctuate
  • Current or voltage is constant (also called “zero frequency component”)
• Alternating Current (AC)
  • Current & Applied Voltage change directions
  • Current or Voltage is time-varying & has no constant offset (also called “non-zero frequency constant”)

We apply this terminology to any signal, regardless of physical meaning

Total Signal - Sum of DC offset & AC components

• DC: Average Value
• Pk: Max Value - Average Value
• Pk-Pk: Peak to Peak Voltage
• $T_o$: Period
• $f_o:\frac{1}{period}$ (Frequency)
• ${\omega }_o:2\pi \ast f_o$