Study Guides/Physics/Difference Between Ammeter and Voltmeter
Study Guide · Physics

Difference Between Ammeter and Voltmeter

When performing experiments in an electricity lab, you will use two very common, similar-looking devices: the Ammeter and the Voltmeter. While they look the same on the outside, their internal construction and purpose are completely different.

Question (Click to Flip)

What happens if I connect an Ammeter in parallel by mistake?

Answer

Because an ammeter has very low resistance, connecting it in parallel will cause a massive amount of current to flow through it instantly, which will create a short circuit and likely burn out the ammeter.

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Key Facts

An ideal ammeter has 0 ohms resistance, while an ideal voltmeter has infinite ohms resistance.

Both devices are essentially modified versions of a sensitive device called a Galvanometer.

1. What do they measure?

  • Ammeter: Measures the rate of flow of electric charge, which is Electric Current. The reading is displayed in Amperes (A).
  • Voltmeter: Measures the electrical potential difference between two specific points in a circuit, which is Voltage. The reading is displayed in Volts (V).

2. How are they connected?

  • Ammeter: It is always connected in Series with the circuit component. This ensures that the entire current flowing through the circuit passes directly through the ammeter so it can be measured.
  • Voltmeter: It is always connected in Parallel across the component you want to measure. It acts as a bridge to measure the difference in potential energy before and after the component.

3. Internal Resistance

  • Ammeter: It has an extremely Low Resistance (ideally zero). If it had high resistance, it would block the current it is trying to measure.
  • Voltmeter: It has an extremely High Resistance (ideally infinite). This ensures that it does not draw the main current away from the actual circuit.

4. Summary Table

FeatureAmmeterVoltmeter
FunctionMeasures Current.Measures Potential Difference.
SymbolA circle with 'A'.A circle with 'V'.
ConnectionSeries.Parallel.
ResistanceVery low.Very high.

Questions and Answers

What happens if I connect an Ammeter in parallel by mistake?+

Because an ammeter has very low resistance, connecting it in parallel will cause a massive amount of current to flow through it instantly, which will create a short circuit and likely burn out the ammeter.

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