Lab Multimeter Operations Reference Cheat Sheet

Key Facts

• Voltage is measured in parallel across a component because the meter compares electric potential difference between two points, written as $V = \Delta U \div q$.
• Current is measured in series with the circuit because all charge flow through that branch must pass through the meter, and current is $I = \frac{\Delta q}{\Delta t}$.
• Resistance is measured with circuit power off because the meter sends a small internal test current and uses $R = \frac{V}{I}$.
• Ohm's law relates voltage, current, and resistance by $V = IR$, so $I = \frac{V}{R}$ and $R = \frac{V}{I}$.
• Electrical power can be found from meter readings using $P = IV$, or with Ohm's law as $P = I^2R$ and $P = \frac{V^2}{R}$.
• For direct current circuits, a negative voltage reading usually means the red and black probes are reversed relative to the chosen polarity.
• Metric prefixes change the scale of readings, so $1\,\text{mA} = 10^{-3}\,\text{A}$, $1\,\text{k}\Omega = 10^3\,\Omega$, and $1\,\text{M}\Omega = 10^6\,\Omega$.
• Continuity mode checks for a very low resistance path, and many meters beep when resistance is approximately $0\,\Omega$ to $50\,\Omega$ depending on the meter.

Vocabulary

Multimeter

A measuring tool that can test electrical quantities such as voltage, current, resistance, and continuity.

Voltage

The electric potential difference between two points in a circuit, measured in volts $\text{V}$.

Current

The rate of electric charge flow through a circuit or branch, measured in amperes $\text{A}$.

Resistance

A measure of how strongly a component opposes electric current, measured in ohms $\Omega$.

Continuity

A test that checks whether there is an unbroken conducting path between two points.

Range

The measurement scale selected on a meter, such as $20\,\text{V}$ or $200\,\text{mA}$, that sets the largest readable value.