Physics·Electricity and magnetism · NSSCO 5.2.3-5.2.4
Resistance & Ohm's law
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Some things let current through easily; others hold it back. That holding-back is resistance, measured in ohms (Ω). In this lesson we define resistance as R = V/I and use the triangle to find any term, state Ohm's law (current is proportional to voltage at constant temperature), and read the three key current–voltage graphs — the straight line of an ohmic resistor, the curve of a filament lamp, and the one-way gate of a diode. We finish with the four things that change a wire's resistance: length, thickness, material and temperature.
What you'll learn in this lesson
By the end you should be able to (NSSCO Physics 5.2.3-5.2.4):
- State that resistance (R) is the tendency of a conductor to oppose the flow of charge, measured in ohms (Ω) using an ohmmeter
- Define resistance as potential difference ÷ current and recall and use R = V/I in calculations
- State Ohm's law — current is directly proportional to voltage (I ∝ V) at constant temperature — and discuss its temperature limitation
- Sketch and interpret current–voltage (I–V) graphs for an ohmic resistor (straight line), a filament lamp (curve) and a diode (one-way)
- State the factors that affect the resistance of a wire: length, cross-sectional area, material and temperature
- Describe an experiment to measure resistance using an ammeter and a voltmeter
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