The terminal voltage of a battery is observed to fall when the battery supplies a current to an external resistor. What quantities are needed to calculate the fall in voltage?
Correct answer: D. The current and the external resistance
- A. The battery's e.m.f and its internal resistance
- B. The battery's e.m.f and the current
- C. The current and the battery's internal resistance
- D. The current and the external resistance
Explanation
d) The current and the external resistance:The current flowing through the external resistor contributes to the voltage drop across the external resistance. The fall in voltage depends on the current and the resistance of the external load. Therefore, knowing the current and the external resistance is necessary to calculate the fall in voltage.
This question appeared on the HEC Phase II 2017 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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