The Electromagnetic Spectrum and Sources of Light.

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The Electromagnetic Spectrum and Sources of Light

What is Light? Light is a form of energy. It is one of several forms of energy we receive from the Sun as part of the solar radiation it produces. The energy from the Sun travels to Earth as electromagnetic waves. These waves can pass through the vacuum of space or materials on the Earth’s surface. Electromagnetic = it affects both electrical and magnetic fields!

Energy in Waves A wave is a disturbance that transfers energy from one point to another without transferring matter. Waves can be described using their physical characteristics and/or properties.

Properties of Waves Crest – the highest point on a wave. Trough – the lowest point on a wave. Rest Position – the level of a fluid (like water) when there are no waves passing through it.

Properties of Waves

The Motion of the Ocean Wavelength ( λ ) – The distance from one place on a wave and the next similar place on the wave. (Crest to crest or trough to trough are most common.) –Wavelength is measured in metres (m). Amplitude – The wave height from the rest position to the crest, OR, the wave depth from the rest position to the trough. –Amplitude shows the energy carried by the wave. Frequency ( ƒ ) – The rate of repetition of a wave. –Frequency is measured in Hertz (Hz) which in cycles per second.

Frequency & Wavelength Frequency and wavelength have an inverse relationship. (As one goes up, the other goes down.) The speed (v) of the wave is determined by multiplying the frequency ( ƒ ) by the wavelength ( λ). v = ƒ x λ

The Spectrum of Visible Light The light that comes from the Sun or a source like a candle is called visible light. It is the light that is visible to the human eye. Over 300 years ago, Sir Isaac Newton passed visible light through a triangular piece of glass called a prism and separated the light into its component colours. The pattern of the colours makes the name “ROY G. BIV” and is known as the spectrum of visible light.

The Visible Light Spectrum

The Electromagnetic Spectrum Visible light is just one type of electromagnetic energy. There are also radio waves, microwaves, X-rays, and gamma rays. All of these are found in the solar radiation of the Sun. ofenergy canAll of the electromagnetic energy can be arranged to form the electromagnetic spectrum. It arranges all of the energy in solar radiation in order from weakest to strongest. Visble light is only a small fraction of the electromagnetic spectrum.

The Electromagnetic Spectrum

Sources of Light

Categories of Light We categorize light based on the source of the light. We say an object is luminous when it emits or produces light. Light may be: –Incandescent –Fluorescent –LEDs –Chemiluminescent –Bioluminescent

Incandescent Light Incandescence is the light produced when an object is heated to a really high temperature. Older light bulbs have a filament, that gets very hot as electricity is passed through it, that gives off the light. These lights are inefficient and not good for the environment because most of the energy put into them is lost as heat (rather than light).

Fluorescent Light Fluorescence occurs when a substance absorbs high energy UV radiation and immediately releases that energy as visible light. A current is passed through the tube of the light. It excites the mercury and argon in side the tube and they give off UV light. This UV light reacts with a chemical that coats the tube and it glows – the chemical coating shows fluorescence!!!

LEDs LED stands for light emitting diode. An electric current passes through an LED and it emits light. LEDs are very energy efficient and are replacing many of the other forms of light. LEDs save energy, last longer and stay cooler.

Chemiluminescence Chemiluminescence occurs when two chemicals react and give off light energy. Light sticks contain two chemicals that mix when you crack the stick and shake it to mix the chemicals. A dye used inside the tube will determine the colour of the stick. Party-goers, campers and law enforcement all make use of this chemical light form.

Chemiluminescence

Bioluminescence Bioluminescence occurs in a living organism. Chemicals produced in the organism are mixed together to produce the light. We see this phenomenon in fireflies, jellyfish, fungi and bacteria.

Bioluminescence

What about the Moon? The moon appears to give off light but it is actually non-luminous – meaning it does not produce its own light. The moon only appears to give off light because it reflects light from a luminous object – the Sun.

Light Off of the Moon

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