What is Light?
Light is an important form of energy for all of us it allows us to see plants rely on light for photosynthesis many chemical reactions produce light life on Earth would not exist without light.
There are two types of light sources Luminous: Luminous light can be from natural or artificial sources. Some examples of natural sources of luminous light are the Sun, the Northern Lights, lava from volcanoes, and light produced from fireflies. Various artificial light sources include computer and television screens, a light bulb, and neon signs. Non-luminous: Some non-luminous sources of light include mirrors, humans, the moon, books, and houses.
Light is produced when another form of energy is converted to light energy. One type of light production occurs when steel is heated to temperatures over 2000 C and it emits white light. The heated steel is said to be incandescent. Substances can also be heated to incandescence by electricity like in an incandescent light bulb Wood, wax, and oil are all forms of chemical energy that can be burned and heated to incandescence.
Sometimes light is produced when electricity flows through a gas. An example of this is the Aurora Borealis, which is seen in the Northern Hemisphere. Streams of charged particles from the Sun colliding with air molecules in the upper atmosphere around the north pole cause the Aurora Borealis.
The lights from neon signs are produced artificially by passing electricity through neon gas within a transparent glass tube. Neon gas produces orange light when electricity is passed through it. Some of the other gases used to produce different coloured lights are sodium vapour that produces yellow light, helium gas that produces white light, and mercury vapour that produces blue-green light. Different gases can be mixed together to produce various types of colours.
Another way of producing light is called chemiluminescence (This method of light production converts chemical energy to light energy). The light produced by glow sticks is an example of chemiluminescence. When chemiluminescence takes place in living organisms, it is called bioluminescence.
Fluorescent light bulbs use a method of producing light called fluorescence. A fluorescent light tube uses this method of producing light. These light tubes are filled with mercury vapour and the inside surface of the tube is coated with a fluorescent powder. Electricity flowing through the tube produces ultraviolet light that hits the fluorescent coating to produce visible light.
People are familiar with objects that glow in the dark such as the dials on some wristwatches and clocks, and glow-in-the-dark stickers. These glow-in-the-dark materials are coated with phosphors, special materials that give off light through a process called phosphorescence. Phosphors absorb light energy, primarily ultraviolet light. These materials keep some of the energy and release visible light of lower energy. However, they do not do so immediately and hold onto this energy for varying periods of time ranging from seconds up to days, depending on the material.
Triboluminescence is the production of light when certain crystals are scratched, crushed, or rubbed. Unlike other methods of producing light, triboluminescence does not appear to have any practical application at this time.
1. a) What is the difference between a luminous and a non-luminous substance? b) Give an example of a luminous and a non-luminous substance. 2. A substance gives off incandescent heat when it is heated to high (a). (b) is a method of producing light by converting chemical energy into light energy in a living organism. Chemiluminescence is the conversion of (c) energy into light energy. Light is produced in a fluorescent tube by converting (d) energy into light energy. The fluorescent tube is filled with (e) vapour.
How Stuff Works - Bioluminenscence
The electromagnetic spectrum is made up of several types of radiation. Two types of electromagnetic radiation are visible light and radio waves. Electromagnetic radiation is made up of photons. Each type of wave in the electromagnetic spectrum consists of photons with different amounts of energy.
For example, the photons in gamma rays have the highest amount of energy and the photons in radio waves have the lowest amount of energy. There are risks involved in exposure to waves in the electromagnetic spectrum with higher energy because these waves can penetrate human tissues and cause damage to cells, mutations, or lead to cancer.
The part of the electromagnetic spectrum that can be seen by humans is called the visible spectrum. The visible white light of the spectrum is made up of several colours each having a different wavelength and frequency. The different waves in the electromagnetic spectrum can be compared to waves of water. Each type of wave will vary in the distance to the next wave. For example the waves in X rays are very close to each other and therefore X rays have a short wavelength.
Visible white light can be separated into the various colours of the visible spectrum with a transparent, colourless, glass prism. The visible spectrum is made up of the colours red, orange, yellow, green, blue, indigo, and violet. The colour red has the longest wavelength and the colour violet has the shortest wavelength. Visible light is only a small portion of the electromagnetic spectrum.
3. The electromagnetic spectrum is a set of (a) that can travel through empty space at the speed of (b). Electromagnetic radiation is made up of packages of energy called (c). 4. List the colours that make up the visible spectrum in order from longest wavelength to shortest wavelength. (a), (b), (c), (d), (e), (f), and (g)..
Humans cannot see the other parts of the electromagnetic spectrum, however, we can use instruments to detect the presence of these invisible regions of the spectrum. The waves with shorter wavelengths such as ultraviolet, X rays, and gamma rays have a higher frequency and a higher energy. The waves with longer wavelengths are radio waves and infrared waves and these waves have a lower frequency and lower energy levels.
Type of Wave Radio waves Description longest wavelength lowest energy level emitted from radio stations, stars, and gases in space Microwaves used in microwaves to cook food used for radar in weather forecasting used in space by astronomers to learn about the structure of nearby galaxies and our Milky Way
Type of Wave Infrared Ultraviolet (UV) X rays Gamma rays Description closest to the red waves in the visible spectrum produces heat things that emit infrared radiation include the Sun, the Earth, a fire, humans and other warm blooded animals, and warm cement the Sun, stars, and other hot objects in space emit UV radiation causes suntans and sunburns medical uses, e.g. X rays can be used by doctors to view bones and by dentists to look at your teeth shortest wavelength highest energy level produced by nuclear processes, e.g. nuclear reactions in stars and radioactive material
5. State the type of wave in the electromagnetic spectrum that relates to each of the following descriptions: produced by nuclear processes has the longest wavelength used by cell phones can be seen by humans used to view bones causes sunburns produces heat
The Electromagnetic Spectrum video How Stuff Works Electromagnetic Waves and Light How Stuff Works Ultraviolet How Stuff Works Harmful Electromagnetic Waves