Study guide: Circuits, Current and Resistance
Calculate idealized circuit quantities without electrical construction.
Ideas to explain in your own words
- Current in amperes equals volts divided by resistance in ohms. The model assumes an ohmic element.
- Series equivalent resistance equals the two supplied resistances added. No physical circuit is needed.
- Two-resistor parallel equivalent resistance equals their product divided by their sum. Parallel branches share voltage.
- Power in watts equals volts multiplied by amperes. Use hypothetical diagrams, not mains electricity.
Useful vocabulary
- A
- Ampere is the SI electric-current unit: one coulomb of charge per second.
- Current in amperes
- Current in amperes equals volts divided by resistance in ohms.
- Ω
- Ohm is electrical resistance of one volt per ampere under the stated circuit model.
- Series equivalent resistance
- Series equivalent resistance equals the two supplied resistances added.
- Two-resistor parallel equivalent resistance
- Two-resistor parallel equivalent resistance equals their product divided by their sum.
- W
- Watt is power of one joule per second.
- Power in watts
- Power in watts equals volts multiplied by amperes.
Watch your reasoning
- Using the distractor operation a*b instead of a/b; Divide voltage by resistance.
- Using the distractor operation a*b instead of a+b; Use this sum only for series connection.
- Using the distractor operation a+b instead of a*b/(a+b); Do not apply the series sum.
A worked review example
Worked distinct example: A distinct model uses 8 V across 4 Ω: I=8/4=2 A. Method: identify the quantities in the stated rule, substitute using compatible units, and perform the operations in the correct order. Divide voltage by resistance. Current and voltage are different physical quantities. Interpret the final unit and keep the model assumption visible; this calculation is not a measurement of a real learner or site. Worked distinct example: A distinct series model has 2 Ω and 6 Ω: equivalent resistance 2+6=8 Ω. Method: identify the quantities in the stated rule, substitute using compatible units, and perform the operations in the correct order. Use this sum only for series connection. Series elements share current, not necessarily voltage. Interpret the final unit and keep the model assumption visible; this calculation is not a measurement of a real learner or site. Worked distinct example: A distinct parallel model has 2 Ω and 2 Ω: (2×2)/(2+2)=1 Ω. Method: identify the quantities in the stated rule, substitute using compatible units, and perform the operations in the correct order. Do not apply the series sum. The result should be below the smaller branch resistance. Interpret the final unit and keep the model assumption visible; this calculation is not a measurement of a real learner or site. Worked distinct example: A distinct model uses 5 V and 0.4 A: 5×0.4=2 W. Method: identify the quantities in the stated rule, substitute using compatible units, and perform the operations in the correct order. Multiply voltage by current. A watt is a joule per second. Interpret the final unit and keep the model assumption visible; this calculation is not a measurement of a real learner or site.
Make a practice plan
- Explain the mechanism in Apply Ohm’s law using a labeled case.
- Complete Combine series resistance and correct the specific misconception in its feedback.
- Resolve a changed case from Combine two parallel resistances, then combine the four ideas in the transfer task.