Question

Which Instrument measures electric current?

• A. Voltmeter
  (B) Ammeter
• B. Barometer
• C. Thermometer

Hint:

Use the unit names to remember the tools: Ampere $\rightarrow$ Ammeter. Volt $\rightarrow$ Voltmeter. This "unit-to-tool" connection makes it easy to remember.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question identifies the specific scientific measuring device used to quantify the flow of electric charge through a circuit.
Step 2: Detailed Explanation:

Function of an Ammeter: An ammeter (short for Ampere-meter) is used to measure the intensity of electric current in a circuit in units called Amperes (A).

Circuit Connection: To measure current accurately, an ammeter must always be connected in "series" with the component whose current is being measured. This ensures that the full flow of electrons passes through the device.

Internal Resistance: An ideal ammeter has zero internal resistance. This is important so that it does not significantly change the total resistance of the circuit and alter the current it is trying to measure.

Analyzing Other Instruments:
- Voltmeter (A): Measures electrical potential difference (voltage) between two points and is connected in parallel.
- Barometer (C): Used to measure atmospheric pressure, typically in meteorology.
- Thermometer (D): Used to measure temperature.

Safety Warning: Connecting an ammeter in parallel with a source can cause a short circuit because of its low resistance, potentially damaging the meter and the circuit.

Step 3: Final Answer:
The ammeter is the instrument designed specifically for measuring the flow of electric current.

Answer 2

Another way to sort these four instruments is by how, or whether, they connect into an electrical circuit at all, since that immediately narrows down which one is built for current measurement.

1. Voltmeter: This connects in parallel across two points of a circuit, its high internal resistance is designed to draw negligible current so it doesn't disturb the voltage it is reading. Its whole design is built around measuring potential difference, not current.
2. Ammeter: This connects in series, directly in the path of the current, and is deliberately built with very low internal resistance so that it does not obstruct the very current it needs to measure fully. That series placement is only useful if the goal is measuring current itself.
3. Barometer: This instrument isn't wired into any circuit at all, it has no electrical terminals, since it's a mechanical or aneroid device sensing air pressure.
4. Thermometer: This too has no standard circuit connection, it senses thermal expansion or, in electronic versions, a temperature-dependent resistance change, but its output is a temperature reading, not a current reading.

Only one of the four is wired in series specifically so that the full circuit current flows through it.

Therefore, the correct answer is Ammeter.