An in-depth explanation of the fundamental concept of Current. Covers current direction, current measurement, and the relationship between current and voltage. A Test Your Knowledge! section is included to enhance the learning process.
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Detailed instructions on how to measure current 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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Circuit elements are commonly categorized as either passive or active. A circuit element is passive if the total amount of energy it delivers to the rest of the circuit (over all time) is non-positive. (Passive elements can temporarily deliver energy to a circuit, but only if the energy was previously stored in the passive element by the circuit.) An active circuit element has the ability to create and provide power to a circuit from mechanisms external to the circuit.
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An electrical system is often used to drive a non-electrical system (in an electric stove, for example, electric energy is converted to heat). Interactions between electrical and non-electrical systems are often described in terms of power. Electrical power associated with a particular circuit element is the product of the current passing through the element and the voltage difference across the element.
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Understanding Nodes in a Circuit
Kirchhoff's current law and Kirchhoff's voltage law are the basis for analysis of lumped parameter circuits. These laws, together with the voltage-current characteristics of the circuit elements in the system, provide us with the ability to perform a systematic analysis of any electrical network. Kirchhoff's current law (commonly abbreviated in these exercises as KCL) states: The algebraic sum of all currents entering (or leaving) a node is zero.
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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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In any electric circuit, our typical goal is to move charges around to perform some useful task. This involves both voltage differences and currents. We create voltage differences in the circuit, which provides energy differences (or electromotive forces) which move charges around, creating currents.
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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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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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Current and Voltage
This topic page covers background material relating to current and voltage.
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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 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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