Resistance characterizes the loss of energy associated with passing an electrical current through a conductive element. A high resistance corresponds to a large energy loss associated with current passage through a material, while low resistance corresponds to small energy loss associated with current passage through a material.
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Detailed instructions on how to measure resistance using a digital multimeter. This topic page also explains the several different settings on a DMM. Includes a Test Your Knowledge! section to practice the material covered.
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Resistors are the most frequently used components in electrical circuits. Since they are so common, they are available in a wide variety of styles and manufacturing techniques. Resistors are manufactured in a variety of ways. Most commonly available commercial resistors are carbon composition or wire-wound; however, resistors on integrated circuits are generally made of semiconductor materials.
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Discussion of how a resistor can either be used as a pull-up resistor or a pull-down resistor to tie a node in a circuit to a known voltage.
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Broad-brush introduction to current, voltage, and resistance as well as how these are related through Ohm's Law. Also the concepts of linear and non-linear behavior are introduced. IV relationship are discussed where a diode is used an an example of a non-linear device.
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In 1827, George Ohm demonstrated through a series of experiments that voltage, current, and resistance are related through a fundamental relationship: Voltage (V) is equal to Current (I) times resistance (R).
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Project 3: Resistors
When resistors are connected in series, the combination has an equivalent resistance that is the sum of the resistances of the individual resistors. This property can be useful in creating desired resistance values from a limited selection of fixed resistors. The user will create a 9 kΩ resistor from the resistors available in the Digilent's® Analog Parts Kit.
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Project 4: Resistors
If the total voltage difference across a set of series resistors is known, the voltage differences across any individual resistor can be determined by the concept of voltage division.
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Project 5: Resistors
When resistors are connected in parallel, the combination has an equivalent conductance that is the sum of the conductance of the individual resistors. The user will create a 5 kΩ resistor from the resistors available in Digilent's® Analog Parts Kit.
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Ohm's Law states that the voltage difference across a resistor is proportional to the current through the resistor. This topic page will guide the user through a set of problems to help understand how to apply Ohm's Law.
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Current Dividers
If the total current into a set of parallel resistors is known, there is an easy way to determine the current through any individual resistor in the parallel combination. The appropriate formula is called the current divider formula, since the total current is divided among the individual resistors.
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Equivalent Resistance
Circuits which consist of resistors connected in parallel can be simplified. This topic page will explain how.
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Voltage Dividers
If the total voltage difference across a set of series resistors is known, there is an easy way to determine the voltage across any individual resistor in the series combination. The appropriate formula is called the voltage divider formula, since the total voltage is divided among the individual resistors.
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Equivalent Resistance
When resistors are connected in series, a simplification of the circuit is possible.
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Voltage-Current Characteristics and Nonlinearities
In this section, we will look at Ohm's law from the standpoint of a voltage-current relationship. This will provide some continuity with our presentation of voltage current relationships for other components, such as capacitors, inductors, diodes, and transistors later on.
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Design Challenge 1: Nominal Resistance Variations
In this exercise, we will be measuring the resistance of several resistors that all have the same nominal resistance in order to determine the actual resistor-to-resistor resistance variations.
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Design Challenge 3: Choosing Resistance
A common problem in designing electric circuits is having to pick a resistance that provides the desired amount of current. In this project, we will create a circuit (i.e. choose a resistor) which results in a specified current being provided by a 5V source.
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Design Challenge 4: Current-Limiting Resistor
Resistors in electrical circuits are commonly used to provide other components in the circuit with the voltages and currents they require in order to function properly. For example, in this exercise, we will design our circuit (i.e. choose a resistance value) to ensure that an LED receives the voltage necessary for it to light up without allowing excessive current, which could burn out the LED.
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Design Challenge 5: Inferring Current From Voltage
Measuring current directly tends to be tedious—you generally need to break open your circuit in order to insert the ammeter into the circuit. Voltage measurements tend to be considerably easier, so it is common to determine the current in a circuit by measuring the voltage across a known resistor and using Ohm's law to estimate the current through the resistor.
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Adding Series Resistors
In this project, we will expand our understanding of resistors in series by finding three fixed resistors—when combined in series, they will provide a specified resistance.
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Power Limitations
Design a resistive network to draw a relatively large amount of power from a source and observe what happens when a resistor fails.
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