Calculate resistor electrical power

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: Power in watts equals volts multiplied by amperes. Formula: a*b. Variable key: a = voltage (V), b = current (A)
• Distinct worked inputs and result: A distinct model uses 5 V and 0.4 A: 5×0.4=2 W.
• Assessment case 1: Supplied case 1: voltage (V)=6; current (A)=2, using the explicitly named quantities. Power in watts equals volts multiplied by amperes. What result follows?
• Assessment case 2: Supplied case 2: voltage (V)=8; current (A)=3, using the explicitly named quantities. Power in watts equals volts multiplied by amperes. What result follows?
• Assessment case 3: Supplied case 3: voltage (V)=10; current (A)=1.5, using the explicitly named quantities. Power in watts equals volts multiplied by amperes. What result follows?
• Assessment case 4: Supplied case 4: voltage (V)=12; current (A)=2, using the explicitly named quantities. Power in watts equals volts multiplied by amperes. What result follows?
• Assessment case 5: Supplied case 5: voltage (V)=15; current (A)=0.5, using the explicitly named quantities. Power in watts equals volts multiplied by amperes. What result follows?
• Assessment case 6: Supplied case 6: voltage (V)=20; current (A)=1.2, using the explicitly named quantities. Power in watts equals volts multiplied by amperes. What result follows?

Learn the idea

Electrical power is voltage times current for this steady model. Power is energy per time, not stored energy. Calculating it does not establish a real component’s safe rating.

Power in watts equals volts multiplied by amperes. The formula in the supplied model is a*b. Variable key: a = voltage (V), b = current (A). Multiply voltage by current. A watt is a joule per second.

A distinct model uses 5 V and 0.4 A: 5×0.4=2 W. Use hypothetical diagrams, not mains electricity. 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)=7; current (A)=2. Expected result: 14 W. Explain what changes and keep this assumption: Use hypothetical diagrams, not mains electricity.

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