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Question

Which one among the following statements related to electric cells is correct ?

This question was previously asked in
CDS 2 2026 Maths Question Paper (13-Sep-2026)
The correct answer is
The emf of a battery is the power provided by the battery per unit current.

Electric Cells: Evaluating Statements on EMF and Properties

This solution evaluates the provided statements regarding electric cells to identify the correct one.

Statement Analysis

  • Option 1: A primary cell is rechargeable.
    This statement is incorrect. Primary cells, like dry cells or alkaline batteries, are designed for single use and cannot be recharged once depleted.
  • Option 2: A secondary cell can be used only once.
    This statement is incorrect. Secondary cells, such as lithium-ion or lead-acid batteries, are designed to be recharged and reused multiple times.
  • Option 3: The emf of a battery is the power provided by the battery per unit current.
    This statement is correct. Electromotive force (EMF), denoted as \(\mathcal{E}\), represents the total energy supplied by the cell per unit charge. It can be expressed as the ratio of power (\(P\)) delivered to the current (\(I\)) flowing through the circuit:

    \(\mathcal{E} = \frac{P}{I}\)

    The unit of EMF is the Volt (V), which is equivalent to Joules per Coulomb (J/C).
  • Option 4: The unit of emf is Joule.
    This statement is incorrect. The standard unit for EMF is the Volt (V). A Joule (J) is a unit of energy or work, while EMF is potential difference per unit charge. Specifically, 1 Volt = 1 Joule per Coulomb (\(1 \, V = 1 \, J/C\)).

Conclusion

Based on the analysis, the only correct statement is that the emf of a battery is the power provided by the battery per unit current.

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