Course:FNH200/Lessons/Lesson 10/Page 10.2

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10.2 What is Radiant Energy?

Radiation refers to the emission and propagation of energy through matter or space by electromagnetic disturbances. These forms of energy are found within the electromagnetic spectrum of radiation (Figure 10.1). This is an organized scale where we find energy ranging from radio waves, microwaves, visible light to ionizing radiation. These forms of energy vary in frequency, wavelength, energy value, penetrating power, and their effects on biological systems.

Figure 10.1. The Electromagnetic. SpectrumAdapted from: Purves et al., 1992. Life The Science of Biology (3rd ed.), Ch. 8. Sinaur Associates, Inc., Sunderland, Mass., p. 164

The longer wavelengths of electromagnetic energy that we are familiar with include visible light, infrared and ultraviolet rays. These are characterized by having low penetrating power. Microwaves and infrared radiation are two examples of the longer wavelengths in the electromagnetic spectrum.

  • Microwaves are used in food for their heating properties. The microwaves travel in straight lines and pass through air, glass, paper and plastic, but reflected by metals. They are readily absorbed by water (polar molecule), causing it to vibrate. Heat is generated by the intermolecular friction generated from the vibrating water (polar) molecules in food. Microwaves are absorbed by food up to a depth of 5 to 7.5 cm.
  • Infrared energy can generate heat. They can reach temperatures above 100°C. Typical examples of infrared energy can be seen in ovens, toasters, and even those "infrared" lamps used to keep food warm.

Examples of short wavelengths include X-rays, beta rays and gamma rays, which can be employed as energy sources in food irradiation, since they have good penetrating power. These forms of energy are referred to as ionizing energy.