In meteorology and weather observation, an anemometer is an instrument used specifically for measuring which physical quantity of moving air?

Introduction / Context:
Anemometers are standard instruments in meteorology, aviation, marine navigation, and wind energy studies. They are commonly seen on weather stations as small cups or blades spinning at the top of a mast. This question checks whether you know exactly which physical quantity an anemometer is designed to measure in moving air. Understanding this helps you correctly associate instruments with the quantities they measure, a frequent theme in general science and competitive exams.

Given Data / Assumptions:

• The instrument mentioned is an anemometer.
• It is used in meteorology and weather observation.
• The context is moving air, often referred to as wind.
• Options mention speed, velocity of currents, pressure, and temperature related ideas.

Concept / Approach:
The word anemos comes from Greek and means wind. An anemometer is therefore literally a wind measurer. In practice, anemometers are calibrated to show how fast the wind is moving past the instrument at a given location and height. They do not directly measure direction, temperature, or pressure, although combined weather stations may include separate sensors for those quantities. The key physical quantity is the wind speed, usually expressed in metres per second or kilometres per hour. Other devices such as barometers and thermometers are used for air pressure and temperature, not anemometers.

Step-by-Step Solution:
Step 1: Recognise that the term anemometer is associated with wind in meteorology.Step 2: Recall that typical cup or propeller anemometers spin faster when the wind blows stronger and more slowly when the wind is gentle.Step 3: These instruments are calibrated in units of speed, such as metres per second or kilometres per hour, to indicate how fast the air is moving.Step 4: Note that ocean currents require different oceanographic instruments, and air pressure is measured by a barometer, not an anemometer.Step 5: Conclude that the primary physical quantity measured by an anemometer is the speed of the wind.

Verification / Alternative check:
Weather reports often mention wind speed together with direction, for example, 20 kilometres per hour from the west. The speed is usually obtained from anemometer readings, while the direction is obtained from a wind vane. Technical manuals and meteorology textbooks also describe anemometers as instruments that measure wind speed. This consistent use of terminology across applications confirms that wind speed is the correct answer and rules out other quantities such as temperature or pressure for this particular device.

Why Other Options Are Wrong:
Velocity of ocean currents is related to water movement, not air, and is measured using current meters in oceans and rivers, so option B is incorrect. Air pressure near the ground is measured by barometers or pressure sensors, not by anemometers, so option C is wrong. Temperature of the atmosphere is measured by thermometers, not by wind measuring instruments, making option D incorrect. Only option A correctly identifies speed of the wind as the quantity measured by an anemometer.

Common Pitfalls:
Students sometimes confuse wind speed and wind direction and assume that an anemometer might measure both. In reality, a separate wind vane is generally used for direction. Another pitfall is to think that any weather instrument might measure pressure or temperature, because those are common weather data. To avoid confusion, remember a simple mapping: barometer for pressure, thermometer for temperature, hygrometer for humidity, and anemometer for wind speed. Fixing these associations in your memory will help in many instrument based questions.

Final Answer:
Speed of the wind