Notes › ENGR 2334: Electric Circuits I Lecture 1
Electric Circuit Variables
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Table of Contents
Electric Circuit
- A circuit is an interconnection of electrical elements linked together in a closed path so an electric current can flow
- electrical elements: battery, resistor, capacitor, inductor (also called devices)
- A terminal of a circuit is also called a node
Current
- We denote current, $\frac{\mathrm{d}q}{\mathrm{d}t}$, as $i$
Direction Matters!
- Current is inverted depending on the direction
- $i_{1} = -i_{2}$
Types of Current
- The behavior of $i$ determines the type of current
- Direct current
- monotonous current; straight line
- Alternating current
- the current varies as a wave function
- single tone, one frequency
- come from alternators
- Rest are signal currents
Charge
$$ q(t) = q(0) + \int_{0}^t i(\tau) \ \mathrm{d}\tau $$Sign Convention
- Used to describe the behavior of circuit elements
Passive Sign Convention
- The circuit element is dissipating/absorbing power
- $i$ goes into (+) terminal
- $\Delta V < 0$
Active Sign Convention
- The circuit element is supplying power
- $i$ goes into (-) terminal
- $\Delta V > 0$
Example
Power
$$P = \frac{\mathrm{d}w}{\mathrm{d}t} = \frac{\mathrm{d}q}{\mathrm{d}t}\frac{\mathrm{d}w}{\mathrm{d}q} = iV$$Net Energy
- The net work/energy done by an element is
Example
References
- Course slides, chapter 1: Electric Circuit Variables
Sources
- Course slides, chapter 1: Electric Circuit Variables