Video: Physics Past Exam • 2017/2018 • Pack 1 • Question 10B

Physics Past Exam • 2017/2018 • Pack 1 • Question 10B

01:26

Video Transcript

State Ohm’s law as a sentence.

Ohm’s law was developed by the German physicist George Ohm. This law came out of his experimental work with conductors. Ohm would take conducting wires, connect them to a power supply, and then measure the potential difference across the circuit, as well as the current that ran through the circuit.

Often we treat conducting wires as ideal with a resistance of zero. But in reality, they do have a resistance and therefore tend to heat up over time as current moves through them. In his experimental work, Ohm was careful to account for the temperature of the conductor in his circuit. He found that when this temperature was constant, when he recorded the potential difference across the circuit, as well as the current in it, Ohm found that these two variables were directly proportional to one another. That is, by doubling one of these parameters, he would find that he’d doubled the other.

Plotted on a pair of axes like this, we can see that these data points have a line of best fit, which is linear. And in fact, the slope of this line of best fit is equal to the resistance in the circuit, 𝑅. We could say then that the change in potential difference divided by the change in current is equal to 𝑅, which is a precursor of the more familiar form of Ohm’s law we sometimes see.

Said as a sentence, we can say that, at a constant temperature, the current in a conductor is directly proportional to the potential difference across the conductor. This is Ohm’s law as a sentence.

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