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Sci 8- Unit 3: Topics 7-8
Transcript of Sci 8- Unit 3: Topics 7-8
Topics 7-8 How does this work? Topic 7: The Wave
Model of Light Page 237 Looking at Wavelength it appears that light is not made up of tiny particles that travel in straight lines as Newton suggests. When light passes through a small opening, it spreads out around each side of the opening. To explain this, Dutch scientist Christiaan Huygens (1629-1695) suggested that light travels in a wave, not as a stream of fast moving particles. The Wave Model of Light The wave model of light pictures light travelling as a wave. It doesn't explain everything about how light behaves but it helps us visualize it. Thinking about light travelling in waves helps to explain unpredictable behaviour, like when light curves around a opening. When light passes through a small opening, the waves spread out. If the wavelength is short, the waves spread out very little, whereas longer wavelengths spread out more Topic 8: Beyond Light Page 249 The Electromagnetic Spectrum Different colors of light represent different frequencies and wavelengths of light. From left to right on the electromagnetic spectrum the colors have a decreasing wavelength and increasing frequency. Visible light energy and all the invisible forms of radiant energy exist on the electromagnetic spectrum. Infrared Radiation Red light has a wavelenth of about 700nm. If you could stretch it out to 1000nm, it would become heat radiation or infrared radiation. Infrared lamps called "brood lights" are used to keep baby chicks warm. Radio Waves Radio waves have a longer wavelength and a lower frequency than visible light. Microwaves have the shortest wavelength and the highest frequency of all the radio waves. When the water particles in the food absorb microwaves, they begin to vibrate quickly and cause the food to become hot. Ultraviolet Radiation (UV) UV has wavelengths of 200nm beyond violet light in the electromagnetic spectrum. In recent years, more and more ultraviolet radiation from the Sun has been reaching the surface of the Earth. This is due to a decrease in the Earth's ozone layer. X Rays At even shorter wavelengths and higher frequencies on the radiant energy spectrum are x rays. X rays pass easily through tissue such as skin and muscle; however, x rays are absorbed by bones. Gamma Rays These rays have the shortest wavelength and the highest energy of all the waves in the electromagnetic spectrum. They result from nuclear reactions and can kill cells. When doctors discover a cancerous tumour in patient's body, they may decide to destroy the tumour with gamma rays referred to as radiation therapy. Light is Energy! Light is nature's way of transferring energy through space. Light travels very rapidly, but it does have a finite velocity. Example: In a vacuum, the speed of light is 186, 282 miles per second. It takes about two and half seconds for a radio communication travelling at the speed of light to get to the moon and back. Remember that light travels in straight lines.
Sir Isaac Newton tried to explain why.
He proposed that light beams are made of streams of extremely tiny, fast-moving particles. These tiny particles of light, he suggested, could only travel in straight lines, not around objects. WRONG! Laser Light we now need to start thinking in terms of wavelengths... Laser light is a device for amplifying light to produce an intense, narrow beam. Explore these images Laser stands for
mplification by the
R Laser light is coherent which means that it has only wavelength with all waves lined up in a similar pattern. The high parts of the wave are called crests.
The low parts of the wave are called troughs.
The distance from crest to crest is called wavelength (the distance from one complete crest and one complete trough). PARTS of the
WAVE MODEL OF LIGHT The height of the crest or the depth of the trough from rest position is called the amplitude.
The Frequency is the rate at which the crest and the trough move up and down.
The number of cycles in a period of time - which is usually measured in hertz, or cycles per second Incandescent light is incoherent which means that it has many different frequencies and wavelengths but the waves are not lined up. QUESTION:
Which one of these wavelenghts
has the bigger 'Amplitude' ? Topic 6-8
Wrap Up - p. 257
Questions 1-9 What can you tell me about each wavelength? Be as detailed as possible! How do X-rays work? 2 min. If these are the wavelengths
we CAN SEE, imagine what we can't....
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