Ohm's Law & Electrical Power Cheat Sheet

Key Facts

• Ohm’s law is $V = IR$, where $V$ is voltage in volts, $I$ is current in amperes, and $R$ is resistance in ohms.
• Current can be found from Ohm’s law using $I = \frac{V}{R}$.
• Resistance can be found from Ohm’s law using $R = \frac{V}{I}$.
• Electrical power is $P = VI$, where $P$ is power in watts, $V$ is voltage, and $I$ is current.
• Using Ohm’s law with power gives $P = I^2R$ and $P = \frac{V^2}{R}$.
• Electrical energy is $E = Pt$, where $E$ is energy, $P$ is power, and $t$ is time.
• In a series circuit, current is the same through each component and total resistance is $R_{\text{total}} = R_1 + R_2 + R_3 + \cdots$.
• In a parallel circuit, voltage is the same across each branch and total resistance follows $\frac{1}{R_{\text{total}}} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3} + \cdots$.

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 through a circuit, measured in amperes.

Resistance

Resistance is how much a material or component opposes the flow of electric current, measured in ohms.

Ohm’s Law

Ohm’s law states that voltage equals current times resistance, written as $V = IR$.

Electrical Power

Electrical power is the rate at which electrical energy is transferred or used, measured in watts.

Electrical Energy

Electrical energy is the amount of energy transferred by a circuit over time, often found using $E = Pt$.