Rob asked in Science & MathematicsPhysics · 1 decade ago

The emf of a battery is equal to its terminal potential difference:?

A) under all conditions

B) only when the battery is being charged

C) only when a large current is in the battery

D) only when there is no current in the battery

E) under no conditions

4 Answers

  • Anonymous
    1 decade ago
    Favorite Answer


    All cells have what is called an internal resistance. When the cell is connected to a circuit a current will flow. The same current that flows in the circuit will also flow in the cell.

    In its ideal form, the cell can be modelled as the emf generator in series with a resistance known as the internal resistance of the cell. The other two ends available: one from the generator and the other from the internal resistance both provide the two terminals you refer to (+ive and -ive).

    We know from Ohms law that when a current flows through a resistor it produces a voltage drop across it; this will also be true of the cell's internal resistance, so there will be a voltage drop across that too. All of which means that there is less voltage available at the cells terminal ends.

    As a result, if no current flows through the cell, then there can be no voltage drop across its internal resistance and hence the terminal voltage will equal the emf of the cell.

    Although not relevant here, the cells internal resistance should be as low as possible.

  • Anonymous
    4 years ago

    For a real battery, this happens whilst there is no modern drawn from the battery. this would propose that any circuit linked between the terminals consists of a change that's open Or the resistance is so great that he modern flowing is virtually 0. basically idealized batteries have a nil inner resistance that would desire to offer the comparable answer.

  • 1 decade ago

    It's kind of a trick question. I'd say 'under all conditions'. When the battery has no charge in it, the difference in potential between the terminals is zero, and so is the EMF. When the battery is fully charged, is has some difference of potential (like 12v for a car battery) and so its EMF is 12 v.

  • 1 decade ago

    D) only when there is no current in the battery

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