Which one of the following instruments is specifically designed to measure solar radiation (solar irradiance) at the Earth surface?

Introduction / Context:
Solar radiation is an important parameter in fields such as meteorology, solar energy engineering, and climate science. Measuring how much solar energy reaches a surface helps in designing solar panels, studying weather patterns, and understanding energy balance. This question asks which instrument is used specifically for measuring solar radiation at the Earth surface.

Given Data / Assumptions:

• We are concerned with instruments that measure physical quantities outdoors.
• The target quantity is solar radiation or solar irradiance.
• Other instruments listed measure different quantities like current or wind speed.

Concept / Approach:
A pyranometer is an instrument designed to measure the total hemispherical solar irradiance on a flat surface, usually expressed in watts per square metre. It uses a thermopile sensor and a dome to capture both direct and diffuse sunlight. By contrast, an ammeter measures electric current, a dynamometer can measure mechanical force or power, and an anemometer measures wind speed. Identifying each instrument and its purpose leads directly to the correct answer.

Step-by-Step Solution:
Step 1: Recall that an ammeter is connected in series in electrical circuits to measure current in amperes. Step 2: Recognise that a dynamometer in mechanical contexts measures force or torque, and in electrical contexts can be part of certain wattmeters. Step 3: Note that an anemometer is used in meteorology to measure wind speed and sometimes direction. Step 4: Identify the pyranometer as the standard instrument used on weather stations and solar farms to measure incoming solar radiation.

Verification / Alternative check:
Descriptions of solar energy measurement systems always mention pyranometers or related radiometers as the primary sensors. The data from pyranometers are used to calculate solar panel performance, determine solar resource maps, and study climate. No other instrument in the option list has this purpose, making the choice unambiguous.

Why Other Options Are Wrong:
Ammeter: Measures electric current, not radiation or energy from the Sun directly. Dynamometer: Measures mechanical or electrical power or force, not solar irradiance. Anemometer: Measures wind speed and sometimes wind direction, not solar radiation.

Common Pitfalls:
Students may confuse the names because many scientific instruments end with meter. It is helpful to associate the prefix pyro or pyra with heat and radiation, which relates to the function of a pyranometer. Another error is to think that an anemometer or another meteorological instrument might also measure radiation, but they are designed for different environmental variables.

Final Answer:
The instrument used to measure solar radiation at the Earth surface is a pyranometer.