Terminal voltage of a cell equals its EMF only when:
Correct answer: A. No current flows
- A. No current flows
- B. Current is maximum
- C. Internal resistance is infinite
- D. Load resistance is zero
Explanation
The lost volts inside the cell are the current multiplied by the internal resistance, so only when the current is zero, that is on open circuit, does the terminal voltage rise to the full emf. This is why a high resistance voltmeter across an unloaded cell reads its emf. Short circuiting the cell does the opposite, making the current maximum and the terminal voltage nearly zero.
This question appeared on the UHS MDCAT 2025 paper, which you can sit online with every answer explained.
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About Internal Resistance of Sources
Internal resistance is the opposition to current inside a cell or other source, causing terminal voltage to fall below its emf when current flows. Questions use E = V + Ir, current in complete circuits, lost volts, source combinations, and the difference between internal resistance and the external load resistance.
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