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Learning Introductory Physics with Activities

Paul J. Emigh, Rebecka Tumblin, Kathryn Hadley, Danielle Skinner

Section 25.9 Electric Current

Subsubsection Key Ideas

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Definition 25.9.1. Electric Current.

Electric Current is the flow of electric charge through space.
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  • Current is a time rate of change. It tells you the rate at which positive charge flows past a given point per unit time: \(I = \frac{dq}{dt}\)
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  • Current is opposite for negative charges. The two currents in the figure below have the same direction, even though the charges are moving in opposite directions, because the charges have opposite signs
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  • Current is measured in amps. Amps are an abbreviation for amperes (A).
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  • Most current flows through electrical conductors. When current is flowing, a conductor is not in Electrostatic Equilibrium.
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A row of positive charges moving to the right and a row of negative charges moving to the left.
Figure 25.9.2. Example: Two rightward currents.
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Subsubsection Activities

Activity 25.9.1. Sensemaking: Units.

What are the units of electric current in terms of other units you have encountered?
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Answer.
C/s
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Activity 25.9.2. Sensemaking: Numbers.

Handheld calculators often use small solar cells to supply the energy required to complete the calculations needed to complete your next physics exam. The current needed to run your calculator can be as small as \(0.30 \mathrm{~mA}\text{.}\) How long would it take for \(1.00 \mathrm{~C}\) of charge to flow from the solar cells?
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Activity 25.9.3. Changing Current.

Consider the positive wire in the Current Example Figure above. Suppose that the charges on the left had a larger speed than the charges on the right. How would the picture change over time?
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References References

[1]
The Sensemaking: Numbers activity adapted from University Physics Volume 2. OpenStax.
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