Science 8 Unit C Section 3.0 Light is part of the electromagnetic spectrum and travels in waves

Section Outcomes: Describe the characteristics and composition of sunlight Explain the wave properties of light and the electromagnetic spectrum Describe some of the technological applications of electromagnetic radiation Recognize the dangers associated with some types of radiation

Section Outcomes: Evaluate, compare and contrast different artificial and natural light sources Describe how primary colours can be added to produce different colours of light

3.1 – The Wave Model of Light When scientists were trying to explain how light works, they could not decide whether or not light was made up of particles or waves Scientists realized that light had a number of properties that are shared with other types of waves

Similarities Between Light and Waves There are two main similarities between light and other types of waves:

Properties of Waves All waves have the same types of properties:

Wavelength, Frequency and Energy As the wavelength of a wave decreases, the frequency of the waves increases As a result, waves with short wavelengths also have higher energies Reason:

Light Waves Scientists such as Newton realized that white light consisted of a number of different colours of light A prism will split up the white light into the visible light spectrum Each colour in the spectrum corresponds to a different wavelength of light

The Visible Light Spectrum

3.2 – The Electromagnetic Spectrum Visible light is just a small part of a larger spectrum The waves of energy that make up light are the same types of waves that also make up other types of radiation The only difference between these types are the wavelength, frequency, and energy of the waves

The Electromagnetic Spectrum

Applications of Electromagnetic Radiation Radio Waves

Applications of Electromagnetic Radiation Microwaves

Applications of Electromagnetic Radiation Ultraviolet Rays

Applications of Electromagnetic Radiation Gamma Rays

3.3 – Producing Visible Light Visible light is important to humans We make use of both artificial and natural light sources

Artificial Light Sources Incandescent Light Bulbs: Fluorescent Light Bulbs:

Phosphorescent Light Phosphorescent lights only light up when ultraviolet light hits it Some substances can store the ultraviolet light energy and release it later This is known as phosphorescence

Incandescent vs. Fluorescent Lights In general, incandescent light bulbs are far less efficient than fluorescent lights In fact, incandescent light generally waste 95% of their energy producing heat In comparison, compact fluorescent light bulbs are about 20% efficient

Natural Light Sources The sun is our most obvious natural light source, but there are many other sources of light For instance, a number of different living things can produce their own light This is known as bioluminescence

Bioluminescence Fireflies Angler Fish

Bioluminescence Jellyfish

3.4 – The Colours of Light Dyes and pigments appear to be certain colours because they absorb all colours of light except for the colour of the dye Therefore, when we mix paint or pigments, we practice subtractive mixing (the more pigments added, the closer the colour comes to black)

Adding Colours of Light However, as we add more colours of light, the closer the mixed colour comes to white The mixing of colours of light is called the theory of colour addition

Primary and Secondary Colours of Light Primary: Secondary:

Television Screens Television and computer screens use additive mixing of light to produce different colours Television screens consist of tiny rows of red, blue and green dots When an image is formed, different combinations of red, blue and green dots light up and produce different colours

Television Screens By changing the brightness of several of these dots, televisions produce a wide range of colours