Section 5.1.3: What are examples of EM radiation?
Radio waves are at the long-wavelength end of the electromagnetic spectrum and were named so because they are used to carry radio and television signals. Radio waves are not readily absorbed by most sorts of matter, and can travel great distances through space; it is for this reason that they have been used successfully in radio astronomy to make some remarkable observations.
Like radio waves, microwaves are used in communications. One of the implications of their shorter wavelength is that a beam of microwaves can be sent in a more precise direction than a beam of radio waves. In the UK, mobile phones operate in the microwave range of the electromagnetic spectrum and microwaves are also used to heat food in microwave ovens.
ACTIVITY: Watch this video about how to measure the speed of light using a microwave oven and a bar of chocolate.
(credit: The Open University)
When an object is heated, it will emit electromagnetic waves with a range of wavelengths depending on the object’s temperature. If the temperature is similar to that found on the surface of the Earth, infrared waves are mainly emitted. Devices that are sensitive to infrared radiation are used for a variety of detection and imaging purposes. One such example is satellite-based remote sensing. The data can be recorded digitally and can be displayed using artificially assigned colours. Some uses of remote sensing are in meteorology, geology, oceanography, pollution control and the study of marine ecosystems.
Infrared radiation is also increasingly used in thermal imaging devices used to ‘see in the dark’ when conditions preclude the use of visible light. For example, rescue workers use thermal imaging devices to detect people in smoke-filled buildings.
Most of the ultraviolet radiation found on Earth originates from the Sun. UV radiation is readily absorbed by objects such as the human body and interacts with the body's chemicals. This is responsible for tanning — an effect that can be reproduced using UV-emitting fluorescent tubes. In small doses, this can be harmless or even beneficial. However, exposure to shorter-wavelength UV waves can be dangerous, leading to melanoma (skin cancer) and to eye cataracts.
(credit: Getty images)
There is no sharp dividing line between X-rays and gamma-rays, and the distinction is usually made with reference to the origin of the radiation, rather than its wavelength. In Earth-bound laboratories, X-rays are produced by bombarding metal plates with electrons, and gamma-rays are obtained from radioactive sources. X-rays have numerous uses, from medical imaging and radiation therapy in hospitals to luggage examination at airports. X-ray computer tomography scanning can now be used to build up a detailed three-dimensional picture of the body by producing images of ‘slices’, even recording soft tissue such as the brain.
(credit: University of Edinburgh)
ACTIVITY: Watch the video below to see what tomography scanning of the brain looks like.
(credit: Shannon Larratt)
ACTIVITY: Use Chromoscope to explore our galaxy in different wavelengths of light