Page 281 - 9.2 A New Way of Thinking About Light
Name/Class:ANSWER KEY
1. What did Sir Isaac Newton propose?
Newton proposed that light beams are made up of streams of extremely tiny fast-moving particles. The tiny particles could only travel in straight lines and that the particles could not travel around objects.
2. What did Dutch scientist Christiaan Huygens propose?
He proposed that light travels as a wave and not as a stream of particles.
3. High parts of the waves are called CRESTS?
4. The low parts of waves are called TROUGHS?
5. What is a wavelength?
A wavelength is the distance from crest to crest or from trough to trough.
6. What is amplitude?
The height of the crest or the depth of the trough from the rest position is the amplitude.
7. What is frequency?
Frequency is the number of cycles completed by a vibrating object in a unit of time.
8. What is hertz?
Hertz (cycles per second)is the unit that frequency is measured in.
9. What is the wave model of light?
The wave model of light is a way of explaining the behavior of light, it involves picturing it traveling as a wave.
10. How can we explain sunsets?
Light waves from the sun travel through the atmosphere of Earth and they strike particles of different sizes (dust and grit as well). Longer wavelengths of oranges and red pass around these particles while shorter wave lengths (blue and violet) strike the particles and reflect and scatter off of them. At sunset light rays travel through many more particles, blue and violet are reflected away while, red and orange waves remain and give clouds their color.
11. What does laser stand for?
Laser stands for: Light Amplification by the Stimulated Emission of Radiaton.
12. What is incoherent and coherent light?
Incoherent light is the crests from one wave overlapping a trough from another, making the waves work against each other.
Coherent light is waves with only one frequency or wavelength and the waves lining up to work together.
13. Where are lasers used?
Lasers are used for: reading bar codes at supermarket check out counters, lazer guns for checking the speed of cars, surgery to repair eyes, in industry to cut through metal, and in fibre optics.
Beyond Light 9.3 – page 293
The Sun radiates visible light that we see, however the Sun also emits invisible energy we don’t see. Visible light energy and all the invisible forms of radiant energy exist on the electromagnetic spectrum.
1. Draw figure 9.20 in your textbook.
2. Which color has the highest frequency and shortest wavelength of light?
The part of the electromagnetic spectrum with the highest frequency is gamma rays (violet). These waves have the shortest wavelength, and therefore many will pass a single point in a given amount of time.
3. Which color has the lowest frequency and longest wavelengths of light?
The part of the electromagnetic spectrum with the lowest frequency is radio waves (red). These waves have the longest wavelength, and therefore fewer will pass a single point in a given amount of time than any other wavelength.
4. Give an example of when you would feel infrared radiation.
You can feel infrared radiation when you bring your hand close to the side of a cup of coffee or hot chocolate, or heat lamp.
5. Give some uses of infrared radiation.
Some uses of infrared radiation are: motion sensors, burglar alarms, infrared heat lamps in restaurants to keep food warm, or an infrared heat lamp to keep baby chicks warm.
6. Why in recent years has more and more ultraviolet radiation been reaching the earth?
More and more ultraviolet radiation has been reaching the earth due to a decrease in the Earth’s ozone layer.
7. List the five types of radiation other than visible light.
Five types of radiation other than visible light are radio waves, infrared radiation, ultraviolet radiation, x-rays, and gamma rays.
8. Identify a use for:
a) Xrays:
X rays are very penetrating and extremely energetic. They can pass easily through tissue (such as skin and muscle) but are absorbed by bone. Therefore they are used for taking pictures of bones etc., to identify possible breaks.
b) Microwaves
· Microwave ovens use microwaves to heat food. They use a specific wavelength or frequency of microwave that is strongly absorbed by water particles. These particles become hot. Only food containing water can be heated in a microwave.
· Microwaves can be used for telecommunications. They can be transmitted to satellites that then amplify the signal and send them on.
· Microwaves are also used in radar. The waves are beamed through the air. When the waves strike an object, they are reflected back. The operator can determine distance to objects based on this fact.
9. Which type of radiation from the Sun causes tanning?
Ultraviolet radiation from the sun causes tanning.
10. Why is the ozone layer important to us?
The ozone layer is important to us because it creates a barrier that blocks some of the harmful UV radiation from reaching earth by absorbing most of it. This radiation can cause problems such as skin cancer, and therefore it is important to protect the ozone layer.