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Free Internal Resistance of Sources MCQs with Answers

10 Internal Resistance of Sources MCQs from Physics, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.

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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10 questions

1. The electromotive force of a cell is

  • A. the same as the potential difference across its terminals when supplying current
  • B. the energy supplied by the cell per unit charge driven round the whole circuit
  • C. the force exerted on the electrons in newtons
  • D. always smaller than the terminal potential difference

Explanation: Despite its name, emf is an energy per unit charge measured in volts, not a force at all.

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Correct answer: the energy supplied by the cell per unit charge driven round the whole circuit

2. A cell of emf 12 V and internal resistance 1 ohm supplies a current of 2 A. The terminal potential difference is

  • A. 12 V
  • B. 14 V
  • C. 10 V
  • D. 2 V

Explanation: The lost volts inside the cell are I times r, that is 2 multiplied by 1, giving 2 V, so the terminal voltage is 12 minus 2, which is 10 V.

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Correct answer: 10 V

3. Terminal voltage of a cell equals its EMF only when:

  • 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…

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Correct answer: No current flows

4. Internal resistance is the resistance offered by________________?

  • A. source of EMF
  • B. conductor
  • C. resistor
  • D. capacitor

Explanation: Internal resistance is the resistance inside a cell or other source of EMF, caused by its electrolyte and internal materials.

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Correct answer: source of EMF

5. Which one of the following is correct for an open circuit?

  • A. Vt=0
  • B. Vt < E
  • C. Vt = E
  • D. Vt = E - Ir

Explanation: In an open circuit, the terminal voltage (Vt) is equal to the source voltage (E).

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Correct answer: Vt = E

6. The opposition offered by the electrolyte of the cell to the flow of current through itself is known as _.

  • A. External resistance
  • B. Internal resistance
  • C. Both
  • D. None

Explanation: The correct answer is internal resistance, which refers to the opposition to the flow of current caused by the materials and reactions…

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Correct answer: Internal resistance

7. The terminal potential difference of a battery is equal to its electromotive force (e.m.f.). whenits internal resistance become

  • A. low.
  • B. zero.
  • C. high.
  • D. constant.

Explanation: The terminal potential difference (V) of a battery is given by the formula \(V=E-Ir\), where E is the electromotive force (e.m.f.), I is…

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Correct answer: zero.

8. The electromotive force of a battery is the voltage between its terminals when

  • A. The circuit is closed.
  • B. The circuit is opened.
  • C. Its circuit resistance is minimum.
  • D. Its internal resistance is maximum.

Explanation: The electromotive force (emf) of a battery is defined as the potential difference across its terminals when no current is flowing through…

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Correct answer: The circuit is opened.

9. The given graph shows the relationship between the potential difference (V) across theterminals of the cell and the current (I) drawn from the cell.The electromotive force (E) and the internal resistance (r) of the cell are

  • A. E = 2 V and r = 0.4 Ω.
  • B. E = 0.4 V and r = 2 Ω.
  • C. E = 0.5 V and r = 0.4 Ω.
  • D. E = 0 V and r = 2.5 Ω.

Explanation: The correct answer is Option B:E = 0.4 V and r = 2 Ω.. In a V-I graph, the y-intercept represents the electromotive force (E) of the cell…

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Correct answer: E = 0.4 V and r = 2 Ω.

10. 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?

  • 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…

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Correct answer: The current and the external resistance
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