Last time we talked about Ohm's Law, V = I R. Which one of these graphs best represents Ohm's Law?
The answer is (a). If you graph voltage vs. current, and you get a linear graph, that means Ohm's law is obeyed.
Ohmic - the material obeys Ohm’s Law (V vs I graph is linear).
Non-Ohmic - the material does not obey Ohm’s Law (V vs. I graph is curved).
We will always assume Ohmic resistors.
Circuits
Circuits are closed paths for charges to flow.
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| An analogy of circuits as a roller coaster ride. |
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| Here's what circuits look like in real life. Every line on the board is a wire. |
Conventional current flows from + to –. Electron flow is opposite ( – to + ).
AC - Alternating Current, direction constantly changes, no + or –.
DC - Direct current, charges only move in one direction.
In this course, we will only be working with DC circuits.
Types of Circuits
Series
- components are connected with one path
- total resistance is the SUM of each resistance.
- The current is the same for all resistors connected in series.
Parallel
- components are connected with multiple paths for charges to flow.
- total resistance is the INVERSE SUM
- The voltage is the same for all resistors connected in parallel.
Using these rules, we can replace a set of resistors with an equivalent resistor
Mixed Circuits
- contains combinations of components in series or parallel
- total resistance must be calculated one section at a time
Kirchhoff's Laws
Kirchhoff's Current Law
Also known as the junction rule.
- All current entering a location must exit that location.
- Current in equals Current out.
I in = I out
Kirchhoff’s Voltage Law
Also known as the loop rule.
- The potential difference around a loop must be zero.
V1 + V2 + V3 + … = 0
Handout
Here are some challenging circuit questions that are more difficult than the ones in your text book.
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