Science 8 Unit C Light & Optical Systems

Unit C Section 1.0Our 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 6th 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:

1.

2.

• 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 (300 000 km/s or 3.00×108 m/s):

Some Properties of Light

• Light has some basic properties:

1.

2.

3.

4.

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 17th 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 17th 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