Which unit is used to measure energy in SI units?

The unit used to measure energy in the International System of Units (SI) is the joule, represented by the symbol J. The joule is defined as the amount of energy transferred when a force of one newton is applied over a distance of one meter. It is a fundamental unit of energy that is widely used in scientific and engineering contexts.

The joule is particularly useful because it provides a consistent framework for expressing energy in various forms, such as electrical, thermal, and mechanical energy. Other units like calories, electronvolts, and kilojoules are also measures of energy, but they are either derived from the joule or used in specific contexts. For example, a calorie is commonly used in nutrition to describe the energy content of food but is not an SI unit. Electronvolts are primarily used in particle physics and are a measure of energy at the atomic or subatomic level. Kilojoules, which are equal to 1,000 joules, are often used for larger quantities of energy but are still based on the joule as the foundation.

Thus, among the given choices, joules is the correct SI unit for measuring energy.