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