Physics · Ch 11 — Electric Current Through Conductors

Ohm's Law

11.5

Ohm's Law

The relationship between the current through a conductor and the potential difference applied across it was first discovered experimentally by the German scientist Georg Simon Ohm in 1828 AD, and is known as Ohm's law. It states: "The current $I$ through a conductor is directly proportional to the potential difference $V$ applied across its two ends, provided the physical state (e.g. temperature) of the conductor remains unchanged."

For a conductor obeying Ohm's law, a graph of current $I$ against potential difference $V$ is a straight line through the origin (Fig. 11.4). Since $I\propto V$ , we may write

$V=IR\qquad\text{or}\qquad R=\frac{V}{I}\qquad\text{--- (11.9)}$ …

Figure 11.4I-V curve for a conductor obeying Ohm's law

What this figure shows. A graph with potential difference V plotted on the horizontal axis and current I plotted on the vertical axis. The plotted curve is a single STRAIGHT LINE passing through the origin (0,0) and rising with a constant positive slope as V increases, with no curvature anywhere along its length. No numeric axis values are printed; the figure's only purpose is to show that for an ohmic conductor the I-V graph is exactly linear through the origin, so the slope (1/R, or equivalently the reciprocal gives R = V/I) is the …

Misc Ex.3Example 11.3 -- Resistance of a flashlight filament from voltage and current

Worked out. A flashlight uses two 1.5 V batteries (giving 3.0 V total) to provide a steady current of 0.5 A in the filament; the worked solution applies R = V/I directly with V = 3.0 V and I = 0.5 A to obtain the resistance of the glowing filament, a direct one-step numeric application of Ohm's law as just defined. …

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