The Electromagnetic Spectrum

The Electromagnetic Spectrum

1. The Wave Model of Light

   • Waves have five main parts. The wavelength is the distance between one crest to another. The height of the wave is referred to as amplitude. The number of waves/s determines the frequency. The highest part of a wave is called the crest, and the lowest part is called the trough.
     • Scientists have been fascinated by rainbows and how they form. You always need sunlight to create a rainbow; this means that light must relate to rainbows. When light shines through a prism, the light breaks up into different colors of light. This occurs because each color refracts at different angles. These colors can be explained using the wave model.
       • The visible light spectrum has red and violet on both ends, with the rest of the colors between them. Red light has a wavelength of 700 nanometres, while violet has a wavelength of 400 nanometres. Colors near violet have shorter wavelengths, while colors near red have longer wavelengths.

2. Producing Visible Light

   • Artificial Sources of Light
     • Incandescent light bulbs have a filament or a thin piece of wire. When the light bulb is turned on, electrical energy flows through the filament, causing the wire to glow. The light you see from the bulb is the filament glowing.
     • Fluorescent light bulbs are glass tubes with gas like mercury vapour. The inside of the bulb is coated with phosphor. Electricity passes through the bulb causing the gas to emit UV light. The UV light then hits the phosphor, which then glows and emits visible white light.
     • Phosphorescence can store energy from the radiation that hits them, allowing them to emit for a long time after the radiation source has ended. Phosphorescence is often used in novelty items. This can explain why glow-in-the-dark toys will eventually grow dim but can be re-energized by merely placing them under a light source like a lamp.
   • Natural Sources of Light
     • The most important natural source of light on Earth is the sun. Without it we could not grow crops, we would be in the dark and we could not grow crops.
     • Bioluminescent animals may produce since they have a light-producing organ or a photophore. Usually, the photophore itself creates the light, but sometimes it is bacteria within the photophore creating light. The light produced by the photophore is sometimes called cool light since it gives off no waste heat.
       • Bioluminescence refers to when organisms produce light. Animals that are bioluminescent or produce light include fireflies, some jellyfish and even fish like the flashlight fish.

3. The Invisible Spectrum

   • The wavelengths making up visible light is only a few compared to the rest of the electromagnetic radiation. At the beginning of the spectrum, there are long wavelengths, whereas, at the end, there are short wavelengths. Human eyes are not sensitive to these wavelengths. As a result, we do not see them
   • Electromagnetic Waves
     • Gamma
       • Gamma rays have the shortest wavelength and the highest energy. They are about the size of the nucleus of an atom. They are extremely dangerous to humans. If a person has been in contact with gamma rays, they could die within the next few hours. However, doctors have used gamma rays to eliminate cancer cells.
     • X-ray
       • X-rays have short wavelengths meaning they have a lot of energy. X-rays can be harmful but we are able to use them to do check-ups on our bones. Our skin is not dense enough to absorb x-rays, but our bones are dense enough, allowing us to see shadows of them. Things in space may emit x-rays. The hotter the object, the shorter the wavelengths will be.
     • UV or Ultraviolet
       • UV light carries more energy than visible light. UV light can cause skin burns or even skin diseases. The ozone layer absorbs the UV rays emitted from the sun, but it is still advisable to wear sunscreen. It is invisible to humans, but some animals can see it. Young stars produce mostly UV light allowing us to detect them. UV light is used for medical and dental, phototherapy and sun tanning.
     • Infrared
       • Infrared waves are approximately the size of a grain of sand. Infrared waves cannot be seen but can be felt as heat. Special equipment can detect infrared radiation allowing us to study heat loss patterns. Images of infrared radiation are called thermograms.
     • Microwave
       • Microwaves are shorter than radio waves; because of this, they have a higher frequency than radio waves. They are usually 1 millimetre to 1 foot long. They are used in microwaves to heat food, weather forecasting and cellphones.
     • Radio wave
       • Radio waves have the longest wavelength of the electromagnetic spectrum, meaning they also have the lowest frequency. They are about the size of a football field. They are used in the radio, television, phones and even radio telescopes.

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