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Bell Work

Bell Work. What happens to light rays when they hit an object? When light rays hit an object, they are either: Reflected Absorbed Transmitted (pass through the object). LIGHT – Benchmarks & Standards. Refraction.

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Bell Work

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  1. Bell Work • What happens to light rays when they hit an object? • When light rays hit an object, they are either: • Reflected • Absorbed • Transmitted(pass through the object)

  2. LIGHT – Benchmarks & Standards

  3. Refraction • When a wave moves from one medium to another medium at an angle, it changes speed as it enters the second medium, which causes it to change direction and bend. The bending of waves due to change in speed is called refraction. Here this pencil appears to be bent inside the glass of water. How many “different” pencils do you see?

  4. How we see...refracted light • When a wave moves from one medium into another at an angle, it changes speed as it enters the second medium, which causes the light ray to bend • Ex: Light wave passing from air to water – RAINBOWS! • Ex: Light wave entering a prism • The bending of waves due to a change in speed is called refraction

  5. What does “Refraction” look like? • Light waves travel fastest through gases • Light waves travel slower through liquids • Light waves are slowed even more as they pass through solids Gas Liquid Gas Solid Gas Liquid Gas Solid

  6. Refraction & LensesSection 18 - 2 • Refraction of light - when light enters a new medium at an angle there is a change in the speed the light is traveling. This causes the light to bend or change direction. • Causes- rainbows, mirages

  7. Prisms • Refract (or bend) light • cause “white” light to separate into its separate wavelengths • we see these different wavelengths as COLOR • The prism splits white light into its different wavelengths. We see these as COLOR

  8. RAINBOW

  9. Refraction of Light • Less dense medium  More dense medium • Light refracted towards normal • Why? Light travels more slowly in a denser medium • Example: air  water • Normal- a line perpendicular (90 degree angle) to the boundary between the two substances.

  10. Refraction of light in water The direction of a ray of light is altered at the boundary of two mediums that have different densities (i.e. air and water). This is called refraction.   Diagram showing refraction of light (also known as the bending of light rays).

  11. Refraction Lab Review of Concepts • A- Magically Appearing Penny • B- Spoon in a Glass • C- Bending Rays • D- Crazy Straw • E- Levitating Penny • F- Focusing Waves • Light ray bent when going from air to glass, glass to water, water to glass, glass to air. • Glass and water more dense than air

  12. Refraction with lenses • The bending of a ray of light also occurs when light passes into and out of a glass lens.However, because of the curved surfaces of the lens, the bending causes the light rays in a beam either to come together (converge, picture on left-hand side) or to spread out (diverge, picture on right-hand side).

  13. Electromagnetic Wave • Transverse waves that have properties of changing electric and magnetic fields • The sun is producing an enormous amount of energy all the time. • This energy pours off the sun as electromagnetic waves and rays. • Different wavelength & frequency = different type of wave • Transfer energy called electromagnetic radiationfrom one place to another • Do NOT require a medium to travel • Can travel through the vacuum of outer space • All EM waves travel at the same speed • “Speed of light” = 300,000,000 m/s

  14. The Electromagnetic Spectrum • EM waves all travel at the same speed, but have different wavelengths and frequencies • 3.7- THE STUDENT WILL USE AN ELECTROMAGNETIC RADIATION SPECTRUM DIAGRAM TO EXPLAIN THAT THE SUNS’ ENERGY ARRIVES AS LIGHT WITH A RANGE OF WAVELENGTHS. [P8C1] • Electromagnetic waves are emitted by the Sun and other stars

  15. Picture Dictation- The electromagnetic spectrum • Radiowaves have the longest wavelengths – they are greater than 10cm. Radiowaves are used for radios, cellphones, televisions, police radars, and in industry to melt materials such as plastics. • Microwaves have a wavelength of 10cm–0.01cm. They are used for heat treatment therapy, alarm systems and heating food. • Infrared radiation has a wavelength 0.01–7 x 10-5cm. It is usually described as heat. The most important source of infrared radiation is the sun, although most heating appliances in your home will emit infrared radiation too. Remote controls have an infrared source and your TV has a detector. •  Visible light has a wavelength 7 x 10-5–4 x 10-5cm. The most common form of visible light also comes from the sun. Other sources are light bulbs and lasers. Lasers have lots of uses, for example in CD players, pointers and laser eye surgery. • Ultraviolet light has a wavelength of 4 x 10-5–10-7cm. The main source of UV radiation is the sun, but it is also generated in industry. It’s used in tanning, dentistry, detecting forged banknotes, and treatment of skin conditions. • X-rays have a wavelength between 10-7–10-9cm. They are used in medicine and airport security. Your doctor uses them to look at your bones and your dentist to look at your teeth. • Gamma rays have the shortest wavelength at smaller than 10-9cm. They are used in medicine as a diagnostic tool and to sterilise equipment. They can be used in industry for food irradiation, searching for oil, measurement of water and soil densities and level detectors, e.g. making sure cans of food are filled to the correct level.

  16. Radio Waves • Radio Waves- carry information and entertainment through radio and television • Longest wavelength • Wavelengths: 10-2 to 106 m • Lowest frequency • Frequency: 106 to 104 Hz • Numbers on your radio tell you what frequency you are listening to! • AM Radio Waves • Range: 600 – 200 m • FM Radio Waves • Range: 5.5 – 0.187 m • Uses: • Amateur and government radio • International broadcasting • Cell Phones

  17. Microwaves • Microwaves- radio waves with the shortest wavelengths and the highest frequencies • Wavelengths: 10-4 to 10-1 m • Frequency: 1012 to 106 Hz • Range: 187 - 10 mm • Uses: • Heating Food Microwave oven- • EM waves bounce around inside the oven, • penetrate the food, • water molecules inside the food absorb the energy, • the food gets hot! • Transmit cell phone calls Microwave radiation can pass through certain materials like plastic and glass, but are blocked by metals, which create sparks and even fire as they bounce off– so no spoons in the microwave!

  18. Infrared Waves • Infrared Rays – the prefix Infra- in Latin means “below,” so the name means “below red” • Invisible to the naked eye • Feel them as heat • Most objects give off infrared rays • Contributes to the Greenhouse Effect • Wavelengths: 10-6 to 10-4 m • Frequency: 1014 to 1012 Hz • Range: 1 mm – 750 nm • Uses: • Heating food • Detecting people or animals in the dark • Studying the growth of plants • Observing motions of clouds to help determine weather patterns A thermograph of an elephant

  19. Visible Light • P8C1- Students know visible light is a narrow band within the electromagnetic spectrum.  I/S • Visible Light- the only part of the EM spectrum that you can see • The portion of the spectrum that allows us to see things in our world; called the “Visible Spectrum” • Wavelengths: 10-7 m • Frequency: 1015 Hz • Range: 750 – 400 nm • Uses: Each wavelength of EM light shows to our eyes as a different color • This visible part of the electromagnetic spectrum consists of the colors that we see in a rainbow - from reds and oranges, through blues and purples. • ROY G BIV • Red, Orange, Yellow, Green, Blue, Indigo, Violet • Longest wavelengths = red  • Shortest wavelengths = violet

  20. Ultraviolet Waves • Ultraviolet Rays – the prefix Ultra- in Latin means “beyond,” so the name means “beyond violet” • Wavelengths: 10-10 to 10-7 m • Frequency: 1016 to 1015 Hz • Range: 400 nm – 10 nm • Uses: Since they have a higher frequency than visible light, they carry more energy • Energy is great enough to damage or kill bacteria or living cells • Small doses provides vitamin D, needed for healthy bones and teeth • Used to treat jaundice (yellowing of skin) • Overexposure can burn skin, cause skin cancer or damage your eyes

  21. X-Rays • X-rays- EM waves with very short wavelengths • Wavelengths: 10-13 to 10-9 m • Frequency: 1021 to 1017 Hz • Range: 10 nm – and below • Uses: Can penetrate most matter • Make images of bones inside the body • X-rays pass through skin and soft tissues and cause the photographic film to darken when it is developed • Denser matter (lead or bone) absorbs X-rays and does not allow them to pass, so image shows up lighter • Airport Security • *Too much exposure can cause cancer

  22. Gamma Rays • Gamma Rays – • Shortest wavelength • Wavelengths: 10-13 to 10-15 m • Highest frequency • Frequency: 1023 to 1022 Hz • Range: < 10-12 m • Uses: Carry the greatest amount of energy, are the most penetrating of the EM waves • Can cause serious illnesses • When used in controlled conditions, can kill cancer cells in radiation treatments • Examine the body’s internal structures Objects far out in space emit gamma rays, which must travel billions of years before reaching Earth

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