V=ir

Definition

The equation v=ir expresses Ohm's Law, which states that the voltage (v) across a conductor is directly proportional to the current (i) flowing through it, with resistance (r) being the constant of proportionality. This fundamental relationship is essential for understanding how electrical circuits operate, illustrating the interplay between voltage, current, and resistance in any circuit component.

5 Must Know Facts For Your Next Test

1. Ohm's Law is applicable to many types of electrical circuits, including both AC (alternating current) and DC (direct current) circuits.
2. In a simple series circuit, the total resistance is the sum of individual resistances, which affects the total current flowing through the circuit.
3. Using v=ir, if the resistance in a circuit increases while the voltage remains constant, the current must decrease.
4. Ohm's Law can be rearranged to calculate different parameters: for example, current can be found using i=v/r and resistance can be calculated as r=v/i.
5. Real-world components may not always follow Ohm's Law strictly; non-ohmic materials exhibit a nonlinear relationship between voltage and current.

Review Questions

• How does changing the resistance in a circuit affect the current when voltage is kept constant?
  • According to Ohm's Law expressed by v=ir, if you keep voltage constant and increase the resistance in a circuit, the current will decrease. This is because resistance opposes the flow of electric charge. Conversely, lowering the resistance while maintaining the same voltage will result in an increase in current. This principle is crucial for designing circuits where specific current levels are required for optimal performance.
• What happens to voltage and current when two resistors are added in series to a circuit, and how can this be analyzed using Ohm's Law?
  • When two resistors are added in series, their total resistance increases. According to Ohm's Law (v=ir), if the voltage remains constant, this increased resistance leads to a decrease in total current flowing through the circuit. The total voltage drop across both resistors can still be calculated as V_total = I_total * R_total. Each resistor will have its own voltage drop proportional to its resistance, which can be analyzed further using individual applications of Ohm’s Law.
• Evaluate how Ohm's Law applies differently when dealing with non-ohmic materials versus ohmic materials in electrical circuits.
  • Ohm's Law is primarily applicable to ohmic materials that exhibit a linear relationship between voltage and current. In these materials, doubling the voltage will result in doubling the current. However, non-ohmic materials do not follow this predictable pattern; their resistance can change with voltage or temperature. For instance, diodes and transistors exhibit non-linear characteristics where small changes in voltage can produce significant changes in current. This distinction is vital for engineers when designing circuits with components that may not behave according to Ohm's Law.

Related terms

Voltage:

The electric potential difference between two points in a circuit, measured in volts, which drives the flow of current.

Current:

The flow of electric charge through a conductor, measured in amperes, representing the rate at which charge is delivered.

Resistance:

A measure of the opposition to current flow in an electrical component or circuit, measured in ohms, influencing how much current will flow for a given voltage.