Eleventh Grade · Science · week 31

Electric Circuits: Current, Resistance, and Ohm's Law

Define electric current and resistance, and apply Ohm's law to solve for voltage, current, or resistance in a simple circuit.

Electric current, I, is the rate at which charge flows past a point: I = Q/t, measured in amperes (A), where 1 A = 1 coulomb per second. Current only flows continuously around a complete, closed loop (a circuit), driven by a potential difference (voltage) from a source like a battery. Resistance (R, measured in ohms) describes how strongly a component opposes that flow -- thin wires, long wires, and certain materials (like the filament in an incandescent bulb) resist more than thick, short, highly conductive wires.

Ohm's law ties these three quantities together: V = I*R, rearranged as needed to solve for whichever one is unknown. A useful (imperfect but durable) analogy: voltage is like water pressure pushing water through a pipe, current is like the resulting rate of water flow, and resistance is like the pipe's narrowness restricting that flow -- more pressure pushes more flow through a fixed pipe, while a narrower pipe reduces flow for the same pressure.

📋 For the teacher
Teach it (10–15 min):
  • If a simple electronics kit, a AA battery holder, a small flashlight bulb (or an LED with an appropriate resistor), and some wires are available, build a basic one-loop circuit together and watch the bulb light when the loop is complete and go dark when it is broken. Without a kit, examine a flashlight or battery-powered toy instead and trace its circuit path by eye.
  • If a multimeter is available, measure the voltage of a few household batteries directly (a fresh AA should read close to 1.5 V) -- a small, satisfying, real measurement that anchors the abstract volt to something concrete.
  • Return to the water-pipe analogy explicitly for every new circuit idea introduced this week and next -- it is imperfect, but remarkably durable for building intuition before the pure math takes over.
  • Work the lightbulb problem (try-item 3) as a genuinely useful real-world skill: estimating the current a household device draws from its printed wattage and voltage, which is exactly the kind of number an electrician uses when sizing wiring or fuses.
Talk about it:
  • Using the water-pipe analogy, what do voltage, current, and resistance each correspond to?
  • Why must a circuit form a complete loop for current to flow continuously?
  • What happens to the current through a resistor if you double the voltage across it while its resistance stays the same?

Mastery looks like: They correctly apply Ohm's law to solve for voltage, current, or resistance given the other two quantities, in a single-resistor circuit.

Common stumbles: Rearranging V=IR incorrectly when solving for a different variable; forgetting that current requires a complete, closed loop to flow at all.

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Records attendance + 15 min of Science for this learner.
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