Difference between revisions of "Ohm's Law"
| Line 23: | Line 23: | ||
\begin{figure} | \begin{figure} | ||
\includegraphics[width=1in]{resistor.jpg} | \includegraphics[width=1in]{resistor.jpg} | ||
| − | \caption{ | + | \caption{A typical (330$\Omega$) resistor} |
\end{figure} | \end{figure} | ||
| − | A resistor resists the flow of electrons, such that a potential (i.e. voltage) is required to produce a current, as described by Ohm's Law above. As per all electronic components, resistors dissipate energy as heat according to the equation: | + | A resistor resists the flow of electrons, such that a potential (i.e. voltage) is required to produce a current, as described by Ohm's Law above. If we imagine electric current flowing as water, a resistor would be a narrow pipe. The higher the resistance, the narrower the pipe, and the harder you will have to push to get a liter-per-second of water through it. As per all electronic components, resistors dissipate energy as heat according to the equation: |
\begin{equation} | \begin{equation} | ||
P=IV | P=IV | ||
| Line 32: | Line 32: | ||
\subsection*{Resistors in Series} | \subsection*{Resistors in Series} | ||
| − | Resistors in series add: | + | Resistors in series add because, in the pipe analogy used above, all the water has to go through all of the pipes, and they all contribute drag: |
\begin{figure} | \begin{figure} | ||
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\subsection*{Resistors in Parallel} | \subsection*{Resistors in Parallel} | ||
| − | Resistors in parallel add reciprocally: | + | Resistors in parallel add reciprocally. In the pipe analogy, water has a choice of which pipe to flow through, and the bulk of the water will be carried by the widest pipe (or for electrons, the lowest-value resistor). Having more paths to choose from will always always reduce drag, but a thin straw next to a firehose isn't going to do much: |
\begin{figure} | \begin{figure} | ||
| Line 62: | Line 62: | ||
\end{figure} | \end{figure} | ||
| + | Resistor values are often encoded on the component using colors. For determining the value of a resistor in Ohms, place the component with the triplet of color bands on the left side, and then read from left to right. For the resistor above, we have red-violet-green. | ||
\begin{figure} | \begin{figure} | ||
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\caption{Matching colors to values} | \caption{Matching colors to values} | ||
\end{figure} | \end{figure} | ||
| + | |||
| + | Match each color with a digit using the chart above (I remember it as "black, brown, ROYGBIV, grey, white", where ROYGBIV is, of course, rainbow ordering). The first two color bands are a two-digit number (e.g. 27 for red-violet above), and the third number is a power-of-ten multiplier (e.g. $10^5$ for green above). Hence the resistor red-violet-green resistor above is a $33\times10^5\Omega$ resistor. | ||
</latex> | </latex> | ||
Revision as of 13:33, 29 August 2012
Short Topical Videos
Reference Material
- Horowitz & Hill, The Art of Electronics, 2nd Ed., Ch. 1
Ohm’s Law
where is voltage, measured in Volts (), with typical values ranging from (into an oscilloscope) to (power lines, severe arcing danger); is current, measured in Amperes (), typical values ranging from (relatively safe for bench-top work) to (very dangerous); is resistance, measured in Ohms (), typical values ranging from (power resistors dissipating a lot of power) to (almost a no-connect).
Resistor
A typical (330) resistor
A resistor resists the flow of electrons, such that a potential (i.e. voltage) is required to produce a current, as described by Ohm’s Law above. If we imagine electric current flowing as water, a resistor would be a narrow pipe. The higher the resistance, the narrower the pipe, and the harder you will have to push to get a liter-per-second of water through it. As per all electronic components, resistors dissipate energy as heat according to the equation:
Resistors in Series
Resistors in series add because, in the pipe analogy used above, all the water has to go through all of the pipes, and they all contribute drag:
Resistors in series
Resistors in Parallel
Resistors in parallel add reciprocally. In the pipe analogy, water has a choice of which pipe to flow through, and the bulk of the water will be carried by the widest pipe (or for electrons, the lowest-value resistor). Having more paths to choose from will always always reduce drag, but a thin straw next to a firehose isn’t going to do much:
Resistors in parallel
Reading Resistor Values
Color band locations on resistors
Resistor values are often encoded on the component using colors. For determining the value of a resistor in Ohms, place the component with the triplet of color bands on the left side, and then read from left to right. For the resistor above, we have red-violet-green.
Matching colors to values
Match each color with a digit using the chart above (I remember it as "black, brown, ROYGBIV, grey, white", where ROYGBIV is, of course, rainbow ordering). The first two color bands are a two-digit number (e.g. 27 for red-violet above), and the third number is a power-of-ten multiplier (e.g. for green above). Hence the resistor red-violet-green resistor above is a resistor.
