Basic Circuits and Measurement

Start with a prediction before touching the meter: if electrical current behaves like water moving through a pipe, what in a circuit acts like pressure, what represents the flow, and what would make that flow harder? Write or discuss your prediction, then use the rest of this lesson to test it. By the end, you should be able to explain why voltage is measured across a component, why current is measured through the circuit, and why resistance must be measured with power removed.

Three components appear in almost every circuit you will build this year. Resistors oppose the flow of current — they limit current to protect sensitive parts, divide voltages, and set bias conditions. LEDs (light emitting diodes) emit light when current flows through them; they are polarized, so the longer lead is the anode (+) and the flat edge of the housing marks the cathode (−). Always use a current-limiting resistor in series with an LED. Capacitors store electrical energy; electrolytic capacitors are polarized and can vent violently if connected backwards.

Voltage (V, volts) is the electrical pressure that pushes charge through a circuit — like water pressure in pipes. Current (I, amperes) is the actual flow of charge — like gallons per minute. Resistance (R, ohms) is opposition to that flow — like a narrow pipe. More pressure means more flow; a narrower pipe means less flow. Current is the same through every part of a series circuit, and no complete path means no current.