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🔋college physics i – introduction review

$I = V/R$

Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025

Definition

The equation $I = V/R$ is a fundamental relationship in electrical circuits, where $I$ represents the electric current, $V$ represents the voltage, and $R$ represents the resistance. This equation, known as Ohm's law, describes the direct proportionality between current, voltage, and resistance in a circuit.

5 Must Know Facts For Your Next Test

  1. Ohm's law is a fundamental principle in electrical engineering and physics, describing the relationship between current, voltage, and resistance in a circuit.
  2. The equation $I = V/R$ can be rearranged to solve for voltage ($V = IR$) or resistance ($R = V/I$), depending on the given information.
  3. The value of current in a circuit is directly proportional to the voltage and inversely proportional to the resistance, as described by Ohm's law.
  4. Ohm's law is applicable to both direct current (DC) and alternating current (AC) circuits, as long as the circuit elements are linear and time-invariant.
  5. Understanding Ohm's law is crucial for analyzing and designing various electrical circuits, including resistive circuits, voltage dividers, and current sources.

Review Questions

  • Explain how the equation $I = V/R$ can be used to analyze the behavior of a simple resistive circuit.
    • The equation $I = V/R$ can be used to analyze the behavior of a simple resistive circuit by allowing you to determine the current, voltage, or resistance in the circuit, given any two of the three variables. For example, if you know the voltage applied to a resistor and the resistance of the resistor, you can use the equation to calculate the current flowing through the circuit. Conversely, if you know the current and the resistance, you can use the equation to find the voltage drop across the resistor. Understanding this relationship is crucial for designing and troubleshooting various electrical circuits.
  • Describe how the concepts of power and energy are related to the equation $I = V/R$.
    • The equation $I = V/R$ is also closely related to the concepts of power and energy in electrical circuits. Power, which is the rate of energy transfer, is defined as $P = IV$. By substituting $I = V/R$ into the power equation, we can derive $P = V^2/R$, which shows that power is directly proportional to the square of the voltage and inversely proportional to the resistance. Additionally, the energy consumed by a resistor is given by $E = I^2Rt$, where $t$ is the time. By substituting $I = V/R$ into the energy equation, we can see that energy is also directly proportional to the voltage and inversely proportional to the resistance. Understanding these relationships between current, voltage, resistance, power, and energy is essential for analyzing and designing efficient electrical systems.
  • Explain how the equation $I = V/R$ can be used to understand the concept of back EMF in the context of 23.6 Back EMF.
    • In the context of 23.6 Back EMF, the equation $I = V/R$ can be used to understand the relationship between the current, voltage, and resistance in a motor or generator. Back EMF, or back electromotive force, is the voltage generated by a motor or generator that opposes the applied voltage, effectively reducing the current flow. When a motor is running, the back EMF generated by the rotating armature creates a voltage that opposes the applied voltage, resulting in a lower current flow than would be expected based on the applied voltage and the resistance of the motor windings. Similarly, when a generator is producing electricity, the back EMF generated by the rotating armature creates a voltage that opposes the applied voltage, limiting the current flow. Understanding how back EMF relates to the $I = V/R$ equation is crucial for analyzing the behavior of motors, generators, and other electromechanical devices.