Apply Ohm’s law

Supplied materials

• All measurements and observations below are supplied classroom examples. They are not data from actual learners or a claim about a particular real site.
• Paper or browser document; an ordinary calculator is optional.
• Rule: Current in amperes equals volts divided by resistance in ohms. Formula: a/b. Variable key: a = voltage (V), b = resistance (Ω)
• Distinct worked inputs and result: A distinct model uses 8 V across 4 Ω: I=8/4=2 A.
• Assessment case 1: Supplied case 1: voltage (V)=12; resistance (Ω)=4, using the explicitly named quantities. Current in amperes equals volts divided by resistance in ohms. What result follows?
• Assessment case 2: Supplied case 2: voltage (V)=18; resistance (Ω)=6, using the explicitly named quantities. Current in amperes equals volts divided by resistance in ohms. What result follows?
• Assessment case 3: Supplied case 3: voltage (V)=24; resistance (Ω)=8, using the explicitly named quantities. Current in amperes equals volts divided by resistance in ohms. What result follows?
• Assessment case 4: Supplied case 4: voltage (V)=10; resistance (Ω)=5, using the explicitly named quantities. Current in amperes equals volts divided by resistance in ohms. What result follows?
• Assessment case 5: Supplied case 5: voltage (V)=15; resistance (Ω)=3, using the explicitly named quantities. Current in amperes equals volts divided by resistance in ohms. What result follows?
• Assessment case 6: Supplied case 6: voltage (V)=20; resistance (Ω)=10, using the explicitly named quantities. Current in amperes equals volts divided by resistance in ohms. What result follows?

Learn the idea

For an ohmic resistor at stated conditions, current equals voltage divided by resistance. Voltage is energy difference per charge; current is charge flow per time. Not every component is ohmic.

Current in amperes equals volts divided by resistance in ohms. The formula in the supplied model is a/b. Variable key: a = voltage (V), b = resistance (Ω). Divide voltage by resistance. Current and voltage are different physical quantities.

A distinct model uses 8 V across 4 Ω: I=8/4=2 A. The model assumes an ohmic element. Track the quantity and unit before calculating. Explain the meaning of a positive, negative or fractional result when relevant. A numerical answer supports the stated model calculation; broader claims require the additional measurements and assumptions described here.

1. Name the measured quantities and their units before substituting values.
2. Write the stated rule and use the variable key to match each symbol to its explicitly named quantity.
3. Calculate each supplied case separately, keeping intermediate arithmetic and the result unit.
4. Explain the result in context and identify the assumption that would invalidate direct use of the rule.

Check your reasoning

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Take it further

Changed-input task: use the same stated model with voltage (V)=13; resistance (Ω)=4. Expected result: 3.25 A. Explain what changes and keep this assumption: The model assumes an ohmic element.

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