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 asks for the name of the specific device used to measure the flow of electric current within an electrical circuit.
Step 2: Detailed Explanation:

• Function of an Ammeter: An ammeter is an instrument designed to measure electric current. Its name is derived from the unit of current, the Ampere (A).
  
• Circuit Connection: To get an accurate reading, an ammeter must be connected in "series" with the part of the circuit through which the current is being measured. This ensures that all the charge flowing through that component also flows through the meter.
  
• Internal Resistance: An ideal ammeter is designed to have zero internal resistance. This is crucial so that its presence in the circuit does not impede the flow of current and alter the measurement.
  
• Analyzing Other Instruments:
  - Voltmeter (A): This device measures the voltage (electrical potential difference) between two points and is always connected in parallel.
  - Barometer (C): This is a meteorological instrument used for measuring atmospheric pressure.
  - Thermometer (D): This instrument is used for measuring temperature.
  
• Safety Warning: Due to its very low resistance, connecting an ammeter in parallel across a voltage source will create a short circuit, which can damage the meter, the circuit, and the power supply.
  

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

Answer 2

This question is asking which instrument is built specifically to measure electric current, so it helps to check each named instrument against what it is actually designed to measure.

1. Voltmeter: A voltmeter measures the electrical potential difference (voltage) between two points in a circuit, and it is connected in parallel across a component. It measures a related but different electrical quantity than current.
2. Ammeter: An ammeter is built specifically to measure the rate of flow of electric charge, current, in Amperes. To read current correctly it must be inserted directly into the circuit path in series, so that every unit of charge passing through that branch also passes through the meter itself.
3. Barometer: A barometer measures atmospheric pressure and has no electrical function whatsoever, it belongs to meteorology, not electricity.
4. Thermometer: A thermometer measures temperature and is likewise unrelated to any electrical circuit quantity.

Of these four instruments, only the ammeter is designed and calibrated to measure electric current directly.

Therefore, the correct answer is Ammeter.