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Engineering
Grade 9-12
Electrical Engineering Basics Cheat Sheet
A printable reference covering voltage, current, resistance, Ohm’s law, power, energy, series circuits, parallel circuits, and basic safety for grades 9-12.
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Electrical engineering basics explain how electric charge moves through circuits and how engineers control that motion to power devices. This cheat sheet helps students connect circuit symbols, units, and formulas in one quick reference. It is useful for solving physics problems, building simple circuits, and understanding everyday electrical systems.
Key Facts
- Ohm’s law is V = I R, where voltage equals current times resistance.
- Electric power is P = V I, and it can also be found with P = I^2 R or P = V^2 / R.
- Electrical energy is E = P t, where energy equals power times time.
- In a series circuit, the same current flows through every component.
- In a series circuit, total resistance is Rtotal = R1 + R2 + R3 + ... .
- In a parallel circuit, the voltage across each branch is the same.
- In a parallel circuit, total resistance follows 1 / Rtotal = 1 / R1 + 1 / R2 + 1 / R3 + ... .
- Kirchhoff’s junction rule says total current entering a junction equals total current leaving the junction.
Vocabulary
- Voltage
- Voltage is the electric potential difference that pushes charge through a circuit, measured in volts.
- Current
- Current is the rate at which electric charge flows, measured in amperes.
- Resistance
- Resistance is how much a material or component opposes the flow of electric current, measured in ohms.
- Power
- Power is the rate at which electrical energy is transferred or converted, measured in watts.
- Series Circuit
- A series circuit has one path for current, so every component carries the same current.
- Parallel Circuit
- A parallel circuit has multiple current paths, so each branch has the same voltage across it.
Common Mistakes to Avoid
- Confusing voltage and current is wrong because voltage is the push on charge, while current is the flow of charge.
- Adding resistors in parallel like series resistors is wrong because parallel resistance must use 1 / Rtotal = 1 / R1 + 1 / R2 + ... .
- Forgetting units is wrong because electrical formulas only give meaningful answers when volts, amperes, ohms, watts, and seconds are used correctly.
- Assuming current is used up by components is wrong because current is conserved in a closed circuit, while energy is transferred to the components.
- Ignoring circuit limits is wrong because too much current can overheat wires, damage components, or create a safety hazard.
Practice Questions
- 1 A 12 V battery is connected to a 6 ohm resistor. What current flows through the resistor?
- 2 A device uses 2 A of current from a 120 V outlet. What power does the device use?
- 3 Two resistors, 4 ohms and 8 ohms, are connected in series. What is the total resistance?
- 4 Why does adding more branches to a parallel circuit usually increase the total current drawn from the power source?