Science 8 Unit C Light & Optical Systems

Unit C Section 1.0 Our knowledge about light and vision comes from explanations, inventions, and investigations.

Section 1.0 Outcomes Identify challenges in explaining light and vision Analyze how microscopes, telescopes, and other optical devices use the properties of light Describe how the development of optical devices contributed to other discoveries in science Investigate light beams and identify phenomena that show the nature of light

1.1 – The Challenge of Light People have been using optical devices for thousands of years Mirrors and lenses were used in ancient China and Greece The Greek scientist Archimedes even developed a plan to use light reflected from mirrors to burn enemy ships in Syracuse harbour! Mythbusters – Archimedes Death Ray Fan Challenge

Early Light Ideas In ancient Greece, a number of people studied light In the 6 th century B.C., a mathematician known as Pythagoras tried to explain how light worked:

Problems With Pythagoras’ Theory:

Euclid & Ptolemy: Euclid discovered two important properties of light: Ptolemy described the action of light as it passed through glass:

al-Haytham & Vision: al-Haytham was an Arabic scientist who studied light In about 1000 A.D., he correctly described how vision worked: al-Haytham also tried to explain how rainbows formed, but he experienced little success

Newton & Light: Sir Isaac Newton studied many aspects of physics and mathematics One major contribution that he made was the discovery of the components of white light:

The Speed of Light Scientists knew that light would travel in straight lines, but they had no idea how fast it traveled The main problem is that old clocks and timing instruments were not accurate enough to measure the high speed at which light traveled There are two solutions to this problem: 1. 2.

Ole Romer Ole Romer used a very large distance to determine the speed of light in 1676:

Albert A. Michelson’s Experiment: In the 1920s, Albert A. Michelson developed an experiment that gives us the currently accepted value for the speed of light ( km/s or 3.00×10 8 m/s):

Some Properties of Light Light has some basic properties:

1.2 – Optical Devices Optical Device: Many optical devices have improved our lives by improving medicine, and by letting us see far into the universe

Microscopes Hans and Zacharias Jansen built the first microscope in 1595 This first microscopes were relatively simple, but led to incredible discoveries In the 17 th century, Antoine van Leeuwenhoek studied many things under his microscope He made the first observations of many cells and organisms, such as:

How a Microscope Works: Microscopes use a series of lenses to magnify an object Recall that the image produced by a microscope is upside- down and backwards

Telescopes Single lenses provided a little closer view of the stars and planets However, the invention of the telescope in the Netherlands in the 17 th century revolutionized astronomy Galileo built his own telescopes to study the stars

Galileo’s Discoveries: Galileo discovered a number of important things about our solar system using his telescope:

Types of Telescopes: Telescopes come in two types: 1.Refracting Telescopes 2.Reflecting Telescopes

The Refracting Telescope

The Reflecting Telescope

Binoculars Telescopes can be bought for home use, but they are usually very large and heavy Binoculars are a smaller, lighter, and more portable solution They provide less magnification than a telescope, however

How Binoculars Work To accommodate for their shorter length, prisms are used to redirect the light along a longer path in the binoculars