Principles of Physics II

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Terminal Voltage

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Principles of Physics II

Definition

Terminal voltage is the potential difference between the terminals of a device, such as a battery or capacitor, when a current is flowing. This voltage can differ from the electromotive force (emf) of the device due to internal resistance and other factors, making it a key concept when discussing real-world applications of electrical devices.

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5 Must Know Facts For Your Next Test

  1. Terminal voltage decreases when a load is connected due to the internal resistance of the power source, resulting in less voltage available for external use.
  2. The relationship between terminal voltage (V), electromotive force (E), current (I), and internal resistance (r) can be described by the formula: $$ V = E - Ir $$.
  3. If no current flows (open circuit), terminal voltage equals the emf since there's no voltage drop across internal resistance.
  4. As load resistance decreases (more current drawn), terminal voltage will continue to drop until it approaches zero as internal resistance dominates.
  5. In practical applications, knowing the terminal voltage is crucial for ensuring devices operate efficiently and effectively without damage.

Review Questions

  • How does terminal voltage change when a load is connected to a battery, and what role does internal resistance play in this process?
    • When a load is connected to a battery, terminal voltage decreases because the internal resistance within the battery creates a voltage drop as current flows. The more current that is drawn through the load, the greater this drop becomes, leading to lower terminal voltage. The relationship can be represented by $$ V = E - Ir $$, where 'I' is the current flowing and 'r' is the internal resistance. Therefore, understanding internal resistance helps explain why terminal voltage isn't constant when devices are in use.
  • Discuss how you would calculate terminal voltage given a specific electromotive force and internal resistance with an applied load. What practical implications does this have?
    • To calculate terminal voltage, you would use the formula $$ V = E - Ir $$, where 'E' is the electromotive force, 'I' is the current flowing through the circuit, and 'r' is the internal resistance of the battery. By measuring or estimating these values, you can determine how much usable voltage remains for your device. This calculation is important in practical applications, like ensuring batteries supply enough power for devices under varying loads without damaging them or causing failures.
  • Evaluate how variations in load resistance impact terminal voltage in real-world electrical systems, including potential consequences.
    • Variations in load resistance significantly impact terminal voltage as they affect how much current is drawn from a power source. When load resistance decreases, more current flows, which increases the voltage drop across internal resistance and lowers terminal voltage. This can lead to devices receiving insufficient power or malfunctioning if their operational thresholds are not met. Understanding this dynamic helps in designing electrical systems that maintain stability and performance despite changing loads.
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