Radio waves are the longest of all the waves in the electromagnetic spectrum. However, they have a lower frequency than the rest of the waves. Radio waves are used for many purposes. There are different types of radio waves depending on the length of their wavelength. Radio waves are not visible to the human eye.

     One type of radio wave are microwaves. Microwaves have a special length of wavelength and frequency that is absorbed by water particles. The water in the food inside the food absorbs the microwaves, and the water particles then become hot. Afterwards, the food heats up. This is how the microwaves inside our home uses microwaves to heat up our food. Since they also long wavelengths, microwaves are also used in radar and communications. The microwaves are first sent to a satellite from a station. The waves are then reflected off the satellite and then the microwaves then reach another station.

     Other radio waves that have longer wavelengths and shorter frequencies than microwaves are used to broadcast television and radio programs. Most of these waves are harmless, they can pass through walls and animals. Today, we have so many television programs and radio programs that even now, there are hundreds of radio waves going through your body!



    

     Infrared radiation has wavelengths longer then red light by about 300 nm (infrared waves have wavelengths about 1000 nm long, while red light has a wavelength of 700 nm). Infrared radiation is also called heat radiation. The waves are also invisible, although you can feel the warmth on your skin when infrared radiation hits it. When an object is warmer then its environment, then infrared radiation is given off the object. You are giving off infrared radiation right now! Many uses for infrared radiation are heat lamps and sensors that sense motion. Infrared radiation can be detected using a technology called thermograms.



Heat lamps like these use infared radiation to help keep chickens warm.

     Visible light is the only type of electromagnetic wave we can see. As you learned already, there are many types of visible light, with different wavelengths and frequencies, red, orange, yellow, green, blue, indigo, and violet. If all of these colours are added together, then white light is created.



A prism separates the colours of white light. The colours and the white light are all visible.

     Ultraviolet radiation have a wavelength shorter than violet light, and a higher frequency as well. Ultraviolet radiation have a wavelength of about 200 nm. Ultraviolet radiation is very energetic, and it causes the particles of the skin in humans to become energetic as well. To protect itself, the skin tans and turns itself darker. However, if there is too much ultraviolet light reaching to your skin, skin cancer might develop. Ultraviolet radiation can also damage the cornea, which is the front part of the eye. The cornea can fog up after being exposed to ultraviolet radiation, and therefore eye vision will be destroyed. To protect the cornea, sunglasses should be worn on hot and sunny days.

     The earth’s atmosphere has a special layer of oxygen that absorbs a lot of the ultraviolet rays from the sun that reaches earth. This is the ozone layer. The ozone layer is like a ultraviolet radiation filter, much of the ultraviolet radiation is absorb, and less ultraviolet radiation reaches the surface of the earth. The ozone layer is good for us, because since less ultraviolet radiation reaches the surface of the earth, there should be less cases of skin cancer and cornea damage. However, in the past few decades, the ozone layer is thinning because harmful chemicals from hairsprays and aerosol sprays are breaking the ozone layer apart. Since the ozone layer is thinning, more ultraviolet rays are reaching the surface of the earth. Therefore, there will be more cases of skin cancer, and the average temperature in the tropics may rise each year, because ultraviolet rays causes things to heat up. Another problem is that ultraviolet rays are now melting the polar ice caps of the world. If this continues, then the water level in the ocean would rise, and maybe in a few hundred years or so, islands and the shores of some countries may become flooded.

As you can see, there is a large hole in the ozone layer on top of Antarctica.

     There are even waves that have wavelengths shorter then ultraviolet radiation. This is called X rays. X rays can go through a lot of material, like the muscles and the skin inside the human body. X rays cannot go through bones, so that is why hospitals and doctors use X rays to see if any bones inside your body is broken or not. They can go through flesh and skin, however X rays cannot go through bone, so therefore your bones will show up. If there is a fracture on the bone, then the doctors can see it using X rays. Dentists also use X rays to check on a person’s teeth to see if they are broken or not.


X rays can help doctors see if a person's bones are healthy or not.

     The waves with the shortest wavelength and highest frequency in the electromagnetic spectrum are called gamma rays. Gamma rays are also the most energetic of all the waves in the electromagnetic spectrum, and that is why they are so dangerous. Gamma rays come from nuclear reactions, and they can kill cells. Therefore gamma rays can be used as a treatment for cancer. If a doctor finds out about a tumour infected with cancer cells inside the body of a person, the doctor may use gamma rays to kill off the cancer cells in the tumour. This type of treatment for cancer is called radiation therapy, and it is becoming more common today. People who work with gamma rays must wear special clothing, which keeps off the dangerous radioactive materials off of humans.

A atomic explosion like this one produces deadly gamma rays.