Scott Huhn, age 10, of St. Louis, Mo., for his question:

WHAT IS AN X RAY?

An X ray is a kind of electromagnetic radiation and it is one of the most useful forms of energy. X rays are used to make radiographs, or X ray pictures, of the bones and internal organs of the body. Radiographs can help a doctor detect abnormalities and disease conditions, such as broken bones or lung disease, inside a patient's body.

Dentists take X ray pictures to reveal cavities and impacted teeth. A radiograph is made by passing a beam of X rays through the patient's body onto a piece of photographic film.

The wavelengths of X rays are much shorter than those of light. For this reason, X rays can penetrate deeply into many substances that do not transmit light. While they are extremely useful in medicine, industry and scientific research, X rays must be used with care since they can cause biological, chemical and physical changes in substances.