SECTION 3 & 4 LIGHT WAVES & INFORMATION TRANSFER

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1 SECTION 3 & 4 LIGHT WAVES & INFORMATION TRANSFER

2 Light Waves Light is a type of energy that travels as waves. Light is different than other waves because it does not need matter to travel. Light waves will bend as it enters water from the air. Light is an electromagnetic wave.

$Light Waves & Sound Sound waves travel around corners better than light waves due to the fact that it bends. Remember when a wave is refracted it means that it bends.$

3 Light Waves & Sound Sound waves travel around corners better than light waves due to the fact that it bends. Remember when a wave is refracted it means that it bends. Sound is created by the back-and-forth motion of objects. Think of a radio, speakers convert the signal into sound because of the back-and-forth motion of the particles.

Electromagnetic Waves Electromagnetic waves are produced by vibrating electric charges. When an electric charge vibrates, its electric field changes, producing a changing magnetic field.

4 Electromagnetic Waves Electromagnetic waves are produced by vibrating electric charges. When an electric charge vibrates, its electric field changes, producing a changing magnetic field. The electric and magnetic field are perpendicular to each other. The changing magnetic field produces a changing electric field. The changing electric field produces a changing magnetic field. And so on and so on and so on...creating a transverse electromagnetic wave.

5 How Electromagnetic Waves Travel Electromagnetic waves do not need a medium to travel through. This means electromagnetic waves can travel through empty space as well as through mediums like air or water!

6 Frequency of Electromagnetic Radiation All forms of electromagnetic radiation travel at the same speed when not in contact with matter. However, different forms of electromagnetic radiation have different wavelengths, and therefore must have different frequencies. There is an inverse relationship between wavelength and frequency. What does this mean? As one value goes up, the other goes down. For example, the longer the wavelength, the lower the frequency.

7 The Electromagnetic Spectrum Electromagnetic radiation is organized by how much energy it carries. The range of electromagnetic radiation is called the Electromagnetic Spectrum. Source: NASA Optional video: can fast forward through it; it is about 32 minutes long Click here to watch a NASA video on the EM Spectrum

8 EM Waves good and bad Ultraviolet light (UV light) is a type of electromagnetic wave produced by the sun. Bad effects: too much exposure to UV light can cause a variety of health problems cancer. Gamma rays can be used to treat some cancerous tumors. Good effects: it kills bacteria on food and surgical tools; produces vitamin D which allows the intestines to absorb calcium.

9 Energy Differences The higher the frequency, the higher the energy. Increasing wavelength Increasing frequency Increasing energy

10 Which of the following forms of electromagnetic radiation has the longest wavelength? A Microwaves B Radio Waves C Visible Light D X-rays

11 Answer Which of the following forms of electromagnetic radiation has the longest wavelength? A Microwaves B Radio Waves C Visible Light D X-rays B

12 Which of the following forms of electromagnetic radiation has the shortest wavelength? A Gamma Waves B Ultraviolet C Infrared D Visible Light

13 Answer Which of the following forms of electromagnetic radiation has the shortest wavelength? A Gamma Waves B Ultraviolet C Infrared D Visible Light A

14 Which of the following forms of electromagnetic radiation has the highest frequency? A Microwaves B Infrared C Ultraviolet D X-ray

15 Answer Which of the following forms of electromagnetic radiation has the highest frequency? A Microwaves B Infrared C Ultraviolet D X-ray D

16 Which of the following forms of electromagnetic radiation has the lowest frequency? A Radio Waves B Ultraviolet C X-rays D Gamma rays

17 Answer Which of the following forms of electromagnetic radiation has the lowest frequency? A Radio Waves B Ultraviolet C X-rays D Gamma rays A

18 Which of the following forms of electromagnetic radiation carries the lowest energy? A Visible Light B Infrared C Radio D Microwaves

19 Answer Which of the following forms of electromagnetic radiation carries the lowest energy? A Visible Light B Infrared C Radio D Microwaves C

20 Which of the following forms of electromagnetic radiation carries the highest energy? A Radio B Gamma C Ultraviolet D Infrared

21 Answer Which of the following forms of electromagnetic radiation carries the highest energy? A Radio B Gamma C Ultraviolet D Infrared B

22 Workbook p. 46 #7 7. When designing devices, engineers need to understand what makes some EM waves safe and others potentially dangerous. Engineers know what the safety of EM waves has to so with their frequency and the energy they carry. More energy means frequency. Higher frequency means danger to human cells. Radio waves are for humans. They are an example of radiation. Ultraviolet light, has a frequency, and it is dangerous to human cells.

23 ANSWER Workbook p. 46 #7 7. When designing devices, engineers need to understand what makes some EM waves safe and others potentially dangerous. Engineers know what the safety of EM waves has to so with their frequency and the energy they carry. More energy means higher frequency. Higher frequency means more danger to human cells. Radio waves are safe for humans. They are an example of low-frequency radiation. Ultraviolet light, has a higher frequency, and it is possibly dangerous to human cells. The higher the frequency, the more energy there is, and the more dangerous the radiation is.

24 Visible Light The only region of the electromagnetic spectrum that human eyes can perceive is the region called visible light. The visible light portion of the electromagnetic spectrum is made up of 6 different colors.

25 Visible Light The colors we see depend upon the wavelength and frequency of the light. Interactions between light and matter produce many common but spectacular effects, such as rainbows and optical illusions. DEMO: prism Visible light waves, like all electromagnetic waves, travel through space until they hit an object and are either reflected, absorbed, or transmitted. Click here to watch Bill Nye explain the nature of colored light.

Workbook p. 48 #11 11.Based on your observations of the prism, select the true statements. A. When light travels through a prism, the light is separated by wavelength. B.

26 Workbook p. 48 #11 11.Based on your observations of the prism, select the true statements. A. When light travels through a prism, the light is separated by wavelength. B. Humans see the different wavelengths of visible light as different colors. C. The prism is being used to combine different colors of light. D. The light bends when it enters the prism and again when it leaves the prism.

27 ANSWER Workbook p. 48 #11 11.Based on your observations of the prism, select the true statements. A. When light travels through a prism, the light is separated by wavelength. B. Humans see the different wavelengths of visible light as different colors. C. The prism is being used to combine different colors of light. D. The light bends when it enters the prism and again when it leaves the prism.

Example: clear glass Translucent materials transmit light but do not let the light travel straight through; the light scatters into different

28 Why Do Objects Have Color? Whether an object is transparent, translucent, or opaque is determined by its ability to transmit light. Transparent materials transmit light straight through, and objects can be seen clearly through them. Example: clear glass Translucent materials transmit light but do not let the light travel straight through; the light scatters into different directions, so an object appears to be fuzzy or distorted. Example: frosted glass Opaque materials do not let light pass through them; instead they reflect light, absorb light or both. Example: wooden door

29 Why Do Objects Have Color? The flowers are mostly opaque. If white light shines on the flowers, all wavelengths of light are absorbed except yellow, which is reflected away and received by the eye. The glass vase is mostly transparent. It appears blue because the pigments in the glass absorb all the colors that compose white light, except blue, which it transmits.

30 Wavelengths of Visible Light Violet light has a frequency almost twice as large as red light, and, therefore, almost twice as much energy.

31 Interactions with Matter When electromagnetic waves collide with matter their direction of motion is altered resulting in three possibilities. You have learned about these before. Can you describe what happens with each?

32 Interactions with Matter Reflection: waves bounce back off the matter; smoother surface better reflection. Absorption: waves can be absorbed by the matter; transfer light energy into matter. Refraction: waves pass through the matter at a different angle due to the wave's change in speed; the light bends or changes direction.

33 Reflection When electromagnetic radiation collides with an opaque surface, the light will reflect back away from the surface. Light reflects away from the surface at the same angle that it hit the surface. DEMO: flashlight & mirror Reflection: angle of incidence = angle of reflection

White objects will reflect all colors of light since white light contains all colors of

34 Absorption of Light When light is incident on an opaque material, some of the light is absorbed and some light is reflected. White objects will reflect all colors of light since white light contains all colors of the spectrum. This is why all projection screens are white! Black objects will absorb all colors of light since black is the absence of light.

35 Demo: Color wheel Mesmerize me!

36 Absorption of Light For each of the diagrams above, explain the color appearance of each object.

37 Separating White Light White light can be separated into colored light if it passes through transparent matter, such as a prism, at an angle. As the light passes through the material it slows down and bends. Because colored light waves have different wavelengths, they bend at different angles, creating the color spectrum to the right. Refraction can separate white light into different colors.

$Refraction When electromagnetic radiation interacts with a transparent material, some of the light will reflect (as it does with an opaque object) but most of the light will refract.$

38 Refraction When electromagnetic radiation interacts with a transparent material, some of the light will reflect (as it does with an opaque object) but most of the light will refract. Refraction is the bending of light as it goes from one material to another material with a different density. The difference in density causes the light to change speed and "bend". Demo: pen in cup

39 Refraction and Perception Refraction of light affects our visual perception of an object's location. When we look at an object under water, light reflects off of the object and then refracts as it passes from water to air, causing objects to appear in a different location. Why does the object appear above it's actual position?

40 Refraction and Perception Refraction of light affects our visual perception of an object's location. When we look at an object under water, light reflects off of the object and then refracts as it passes from water to air, causing objects to appear in a different location. Why does the object appear above it's actual position? Reflected light waves bend away from the normal as light waves speed up going from water to air.

41 Light Wave Behavior Go through each tab and review the information ghtbehaviors/

42 Lenses A lens is a clear optical tool that bends light. Lenses affect how we see images. They can cause objects to appear closer or farther away. The type of image depends on the shape of the lens and how close the object is to the lens.

43 Convex Lens A convex lens is thicker at the center than at the edges. Convex lenses are used to magnify or focus light, so they are used in tools such as magnifying glasses, telescopes, and microscopes. Also is used to help with farsightedness.

44 Concave Lens A concave lens is thinner at the center than at the edges. Concave lenses are used to spread light, often in combination with other lenses in telescopes and binoculars. Also is used to help with nearsightedness.

45 Test Sections 3 & 4 Link for Games on the last slide

46 Games Review Games select a game to review waves information

Grade 8 Science: Unit 3-Optics Chapter 4: Properties of Light

Grade 8 Science: Unit 3-Optics Chapter 4: Properties of Light Key Terms: Microscope, telescope, amplitude, crest, energy, force, frequency, hertz, medium, transverse wave, trough, wave, wavelength, reflection,