science8 unit c lightand optics section1 lesson1 the challengeof light

Science 8Unit C: Light and Optical Systems

Science InAction 8

Our knowledge about light and vision comes from explanations, inventions, and investigations

Section 1.1: Pages 174-181

The Challenge of Light 1.1

Learner Outcome

Students will identify challenges in explaining the nature of light and vision

Light Light is energy Our eyes are able to

see an object only if light is emitted from the object or bounces off it

Light travels in straight lines and needs a direct path

Early Greeks and Chinese used mirrors to refract the light from the sun using mirrors.

Early Light Ideas Pythagoras –

mathematician – tried to explain how we see light

He thought light consisted of beams that came from a persons eyes in straight lines

Problem = If light came from a persons eyes we would be able to see in the dark

This theory was accepted for many years

Euclid Euclid - Greek

mathematician Discovered that when you

shine a beam of light onto a flat mirror, the angle between the incoming beam and the mirror is equal to the angle between the reflected beam and the mirror

Suggested that light travels in straight lines

Light Ideas in the Middle Ages

A.D. 1000, Arab Scientist al-Haytham took up the study of light.

Wrote a book on optics Discovered that light

bounces off objects and then travels to the eye

Pythagoras’s theory was abandoned after his discovery

Newton’s Light Experiment

Rainbow experiment Newton showed that

white light is actually a mixture of different colors of light

As light is passed through a prism, it is split up into many separate colors

Showed that separate colors combined back into white light

A Speedy Discovery Ole Romer in 1676

estimated the speed of light

Albert A. Michelson refined his measurement in an experiment involving 2 mirrors on top of mountains in California in the 1920’s

Page 181

Calculating the Speed of Light - c

Velocity formula v=d/t Or… d=v*t Or… t=d/v

Mirrors apart = 35.4 km

Light was calculated to be 299, 798 km/s

or ~ 300 000 km/s

What was the time it took to travel from one mountain to the other?

Galileo’s Experiment: Later refined by Romer and Michelson

Michelson–Morley experiment

The Properties of Light

1. Travels in straight lines

2. Can be reflected

3. Can bend

4. Is a form of energy

Did you…

identify challenges in explaining the nature of light and vision?

Check and Reflect Questions 2-5, page 181

2. What was Pythagoras’s theory of how we see light?______________________________________________________

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3. What was the problem with his theory?______________________________________________________

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Check and Reflect Questions 2-5, page 181

4. What did al-Haytham try to explain?___________________________________________________

______________________________________________________________________________________

5. Based on Michelson’s measurement of the speed of light, if the distance between the sun and the earth is 149 596 000 km, how long does it take light to travel from the sun to the earth?