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8th Grade Science Unit 6: Electromagnetic Radiation
www.njctl.org
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Table of Contents
· Interactions with Matter
· What is Electromagnetic Radiation?
· The Electromagnetic Spectrum
Click on the topic to go to that section
· Visible Light
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SLIDE 2 What is Electromagnetic Radiation?
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Electromagnetic Radiation
What do X-rays, light, microwaves, radio waves, and infrared have in common?
Slide 5 / 121 Electromagnetic Radiation
Radiation can be described as the movement of energy through space. There are many different sources of radiation that vary by intensity. The Sun, light bulbs, nuclear reactions, and radon gas, are all sources that produce electromagnetic radiation.
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SLIDE 3 Electromagnetic Radiation
We are constantly bombarded by electromagnetic radiation, most of which we cannot see.
http://www.epa.gov/radtown/enter-radtown.html
Note
Slide 7 / 121 Electromagnetic Radiation
The electromagnetic radiation we interact with is not all bad. When you cook food in a microwave, listen to music, see colors,
- r feel heat you are experiencing electromagnetic radiation.
How does electromagnetic radiation travel through space?
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Electromagnetic Radiation
One way electromagnetic radiation travels through space is as a wave. Electromagnetic waves are different from mechanical waves because they don't need a medium to travel through. What's "waving" in an electromagnetic wave?
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SLIDE 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 perpendicular to it, the changing magnetic field produces a changing electric field produces a changing magnetic field produces a changing electric field produces a changing magnetic field... creating a transverse electromagnetic wave
Slide 10 / 121 How Electromagnetic Waves Travel
Electromagnetic waves do not need a medium to travel through. This means electromagnetic waves can travel through anything, such as in air, water, or even mostly empty space! Electromagnetic waves also do not lose energy as they travel unlike mechanical transverse waves which lose some
- f their energy to their medium.
An electromagnetic wave continues to go straight and spread out until it collides with some form of matter, at which point the direction of travel will change.
Slide 11 / 121 Electromagnetic Wave Characteristics
Electromagnetic waves have the same wave characteristics we studied last unit: wavelength ( ) measured in meters frequency (f) measured in Hz speed (c) 300,000,000 meters/second Wavelength and frequency vary based on the type of electromagnetic wave, but all electromagnetic waves travel at the same speed in a vacuum. What is a vacuum?
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SLIDE 5 The Vacuum of Empty Space
A vacuum is a space that is completely empty, containing no matter. A true vacuum does not actually exist because even nearly empty parts of the Universe contain some matter. The closest thing to a vacuum that has been produced in a lab is a space that has one billionth of one billionth of the standard pressure of the atmosphere!
Slide 13 / 121 Speed of Electromagnetic Radiation
Scientists use the idea of constant speed (c) in a vacuum because it's useful for
- calculations. c is also refered to as the
speed of light. In theory, nothing can travel faster than the speed of light (maybe?). In reality, any matter an electromagnetic wave encounters will slow it down. If you could travel at the speed of light, you could go around the Earth's equator 7.5 times in one second.
Slide 14 / 121 Wavelength of Electromagnetic Radiation
Different types of electromagnetic radiation have different wavelengths. A wavelength is the distance between adjacent crests.
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SLIDE 6 Frequency of Electromagnetic Radiation
Since all forms of electromagnetic radiation travel at the same speed when not in contact with matter but have different wavelengths, then different forms of electromagnetic radiation also have different frequencies. There is an inverse relationship (opposite) between wavelength and frequency. The longer the wavelength, the lower the frequency.
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Relationship Between Speed, Wavelength, and Frequency
A wave's frequency or wavelength can be solved for using the wave equation from last unit: The only difference is that since all electromagnetic radiation travels at the speed of light, then v can be replaced with this value every time, represented by the letter c, which equals 300,000,000 m/s. We use the new wave equation to solve for the frequency or wavelength of electromagnetic waves based on the equations below:
Click here to see how to prove the speed of light using chocolate and a microwave.
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1 If you could travel at the speed of electromagnetic waves in a vacuum, how long would it take you to travel from the surface of the Earth to the Moon? speed = c = 300,000,000 m/s distance between Earth and Moon = 356,400 km or 356,400,000 m t = d/s
Answer
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SLIDE 7 2 The Sun is 149,600,000 km away from the Earth. How many minutes ago did the radiation that is hitting you right now leave the Sun? c = 300,000,000 m/s 1000 m = 1 km 60 seconds = 1 min
Answer
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3 Radio waves are electromagnetic waves with long
- wavelengths. If an AM radio wave's frequency is
540,000 Hz, what is its wavelength? Is it long enough to bounce over the Empire State Building (381 m)? c = 300,000,000 m/s
Answer
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4 What is the frequency of a radio wave that has a wavelength of 1 cm (0.01 m)?
Answer
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SLIDE 8
5 An electromagnetic wave has a frequency of 1.5 GHz (1,500,000,000 Hz). What is the wavelength of the wave?
Answer
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6 Red light has a frequency of 4.6 x 1014 Hz (460,000,000,000,000 Hz). What is the wavelength of red light?
Answer
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7 Which of the following electromagnetic wavelengths would have the highest frequency? A 100 m B 10 m C 1 m D 0.1 m
Answer
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SLIDE 9 8 Which of the following frequencies would have the shortest wavelength? A 1000 Hz B 100 Hz C 10 Hz D 1 Hz
Answer
Slide 25 / 121 Electromagnetic Radiation
Electromagnetic radition can also travel through space in packets of energy called photons. In high school physics you'll learn more about how electromagnetic radiation can be both a wave and a particle...
Slide 26 / 121 The Electromagnetic Spectrum
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SLIDE 10 The Electromagnetic Spectrum
Electromagnetic radiation is organized by how much energy it carries. The range of electromagnetic radiation is called the Electromagnetic Spectrum. Click here to watch a NASA video on the EM Spectrum Note
The first 5 minutes of the video provide a perfect introduction to the EM spectrum and review of previous concepts. The entire video is 35 minutes long, so you may suggests students watch the rest on their own.
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The Electromagnetic Spectrum
The different types of electromagnetic waves from that make up the spectrum are from left to right: Radio, Microwave, Infrared, Visible Light, Ultraviolet, X-ray and Gamma ray
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Energy Differences For Types of Electromagnetic Radiation
The higher the frequency, the higher the energy. Which type of electromagnetic radiation has the highest energy?
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SLIDE 11
9 Which of the following forms of electromagnetic radiation has the longest wavelength? A Microwaves B Radio Waves C Visible Light D X-rays
Answer
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10 Which of the following forms of electromagnetic radiation has the shortest wavelength? A Gamma Waves B Ultraviolet C Infrared D Visible Light
Answer
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11 Which of the following forms of electromagnetic radiation has the highest frequency? A Microwaves B Infrared C Ultraviolet D X-ray
Answer
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SLIDE 12
12 Which of the following forms of electromagnetic radiation has the lowest frequency? A Radio Waves B Ultraviolet C X-rays D Gamma rays
Answer
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13 Which of the following forms of electromagnetic radiation carries the lowest energy? A Visible Light B Infrared C Radio D Microwaves
Answer
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14 Which of the following forms of electromagnetic radiation carries the highest energy? A Radio B X-ray C Ultraviolet D Infrared
Answer
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SLIDE 13 15 Which of the following forms of electromagnetic radiation travels fastest through a vacuum? A Radio B X-ray C Ultraviolet D All travel the same speed
Answer
Slide 37 / 121 Radio Waves
Radio Waves were first mathematically theorized to exist by James Clerk Maxwell in 1864. They were not actually discovered until 1888 by Heinrich Hertz when he experimentally determined the electromagnetic waves he produced in a laboratory had different wavelengths than light but reflected and refracted in the same manner.
Slide 38 / 121 Radio Waves
Radio waves have the longest wavelengths of all electromagnetic
- waves. The wavelength
- f a radio wave
measures anywhere from approximately 20 cm to the diameter of
waves have the longest wavelengths, they also have the lowest frequency, and therefore the lowest energy. We can thank radio waves for much of the navigation technology in use today!
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SLIDE 14 A radio needs two parts: a transmitter and a reciever.
How We Hear Radio Waves Slide 40 / 121
The transmitter encodes information
changing a property of the
sends the wave
antenna.
How We Hear Radio Waves Slide 41 / 121
A radio receives the signal when the antenna of the receiver picks up the wave. The receiver then decodes the information contained on the wave and turns the wave into a mechanical wave that vibrates the speakers accordingly.
How We Hear Radio Waves Slide 42 / 121
SLIDE 15
Slide 43 / 121 Why does FM Radio Sound Clearer?
FM radio stations transmit waves that have smaller wavelengths than AM stations, so they have a higher frequency. Since an FM station is changing the frequency of the wave and not the amplitude, more information can be encoded on the transmitted wave, creating a clearer signal.
Slide 44 / 121 How TVs use Radio Waves
When you watch TV, you can change the channel just like when you change the channel on the radio. TV channels encode their broadcast onto radio waves in a manner similar to FM stations, by changing their frequency. A TV wave has a smaller wavelength than an AM Radio transmission, but larger than an FM transmission. There is a receiving dish at the cable company that picks up the signal and then encodes it again by changing the frequency sent out through coaxial cables or light pulses, which are used in fiber optics.
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SLIDE 16 Radio Waves from Outerspace
Objects in space like stars and galaxies emit radio waves. NASA has built sophisticated radio telescopes to listen in on the universe and learn about far away
- bjects' structure and motion
without interference from our
- atmosphere. Maybe one day aliens
will contact us via radio signal?
Slide 46 / 121 Microwaves
Microwaves are a form of electromagnetic radiation that have shorter wavelengths than Radio waves (wavelengths range from 1 mm to 1 m). Microwaves have the name "micro" because their wavelength is shorter than Radio Waves. Since Microwaves have shorter wavelengths and higher frequencies they can carry more information. Microwaves are used for: Communications Radar Navigation Heating Radio Astronomy
Slide 47 / 121 Microwaves Used In Communications
Since microwaves transmit at a frequency between 300 MHz and 300 GHz, they are useful for transporting information at a rapid rate. This allows wireless communication through either cordless phones or cellphones which work
- n frequencies near the 1 GHz (1,000,000,000
Hz) range on average. These types of devices contain both transmitters and receivers. Since the wavelength received is so small, the antenna size can also be smaller. Due to this technology other devices such as bluetooth and WiFi work at a frequency of around 2.5 GHz. Thanks microwaves for making instagram possible!
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SLIDE 17 Slide 49 / 121 Doppler Radar
If the object is moving, the microwaves will change frequencies just as in the Doppler Effect studied in Sound Waves. Based on the frequency received compared to that transmitted, the speed of an
- bject (or weather pattern) can be determined.
Slide 50 / 121 Microwaves used in Heating
Microwave Ovens were actually discovered on accident in 1945. Using British technology, an American engineer at Raytheon was doing Radar experiments when he discovered that a
- Mr. Goodbar chocolate bar in his pocket
had started to melt. Microwaves use the energy they carry to heat food. Water and fats inside the food absorb the energy and begin to rotate. As these molecules spin they transfer the absorbed energy to other parts of the food, causing the food to heat up.
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SLIDE 18
16 Radio receivers do not have to be directly in line with transmitters because diffraction allows radio waves to bend over hills and buildings to reach receivers. This works with better with radio waves than other types of electromagnetic waves because radio waves have A high frequency B shorter wavelengths C longer wavelengths D higher speeds
Answer
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17 Which type of electromagnetic wave is used to transmit cell phone signals? A Radio waves B TV waves C Microwaves D Gamma rays
Answer
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18 Microwaves have higher data transmission rates than radio waves because A They have a lower frequency B They have a higher frequency C They travel at a higher speed D They have a longer wavelength
Answer
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SLIDE 19
Light
Light makes up the middle region of the electromagnetic spectrum, which have shorter wavelengths and higher frequencies and energy than radio waves. Infrared Visible Light Ultraviolet There are three types of light that make up this region:
Slide 55 / 121 Infrared Light
Infrared Light has the longest wavelengths of any light and, therefore, the smallest amount of energy. The term infrared means "below red" and refers to the fact that Infrared Light has a smaller wavelength than red light. Humans cannot see Infrared light with the naked eye, but can feel infrared's energy in the form of heat on their skin. Common uses for Infrared Light include: Remote Controls Thermal Cameras Night Vision Goggles
Slide 56 / 121 Infrared Radiation as Heat
Infrared radiation was discovered in 1800 by William Herschel when he conducted an experiment to see how the temperature of visible light changed based on color. What he found was that red light was warmer than violet light, but that there was also a region beyond red light that was even hotter. This region of heat is known as the Infrared Region. Click here to see how Herschel discovered infrared radiation
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SLIDE 20 Infrared radiation is emmitted by
- bjects when they give off heat.
Hotter objects, such as fire, give
- ff visible light as heat, but not all
- bjects that give off heat do so in
the form of visible light.
Thermal Imaging
Humans and animals emit heat that cannot be seen by the naked eye because it is in the Infrared Range. Thermal imaging cameras and night goggles however can detect this heat and transform the different levels of heat into different colors on their displays.
Slide 58 / 121 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, 3 primary and 3 secondary. By blending these colors together, additional colors can be made.
Slide 59 / 121 Wavelengths of Visible Light
The portion of the electromagnetic spectrum that human eyes can see is actually very
has wavelengths that measure between *400 nm (violet) to 700 nm (red). This means that violet light has a frequency almost twice as large as red light, and, therefore, almost twice as much energy. *A nanometer (nm) is equal to 1x10-9 meters or 0.000000001 meters
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SLIDE 21 Ultraviolet Radiation
Ultraviolet radiation is a form of electromagnetic radiation that has a shorter wavelength than visible light and is therefore undetectable by the human eye, although some birds and insects can see some wavelengths in the UV range. The range of UV wavelengtht is 400 nm down to 10 nm.
http://www.bbc.co.uk/nature/18580667
The right side shows what birds with UV perception can see.
Slide 61 / 121 Types of UV Radiation - UVA
Ultraviolet A (UVA) waves have a wavelength between 400 and 315 nm. UVA rays account for 95% of the ultraviolet radiation that reaches Earth's
- surface. UVA rays are present with
equal intensity at all daylight hours throughout the year and can penetrate both clouds and glass. It is the UVA rays that are the primary reason skin will "tan". Tanning is the body's defense against further damage to DNA caused by UVA rays.
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Ultraviolet B (UVB) waves have a wavelength between 315 and 280 nm. UVB rays intensity varies depending on time of day, year and location. In the United States, UVB rays are at their highest intensity from 10 AM to 4 PM during the months of April to October. UVB are more intense at higher elevations and on reflective surfaces, such as snow or ice. UVB rays do not penetrate glass.
Types of UV Radiation - UVB Slide 63 / 121
SLIDE 22 Ultraviolet C (UVC) waves have a wavelength between 280 nm and 100 nm. Most UVC rays are absorbed by the Earth's atmosphere and do not reach the surface of the Earth.
Types of UV Radiation - UVC Slide 64 / 121 Effect of UV Radiation on Humans
UVA and UVB rays have adverse effects on humans. Both types of radiation cause premature aging of the skin and skin cancer. UVA radiation is more prevalent than UVB radiation.
Slide 65 / 121 Protection from UV Radiation
To protect against the harmful effects of UVA and UVB radiation, it is recommended that sunscreen with a SPF rating of 15 or higher be used. The SPF (Sun Protection Factor) rating
- n a sunscreen is a measure of how
long it would take UVB rays to redden the skin compared to if there were no sunscreen applied. For example, someone using a sunscreen with an SPF of 15 will take 15 times longer to redden than without the sunscreen. SPF 15 blocks 93% of UVB rays, while SPF 30 blocks 97% and SPF 50 blocks 98%.
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SLIDE 23
19 Human can see which of the following types of light A Infrared B Visible Light C Ultraviolet Light D All of the above
Answer
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20 Within the light part of the EM Spectrum, _________ light has the longest wavelength. A Infrared B Red C Ultraviolet D Violet
Answer
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21 Which type of visible light has the highest energy? A Red B Orange C Green D Violet
Answer
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SLIDE 24
22 UV rays cannot penetrate clouds to reach Earth's surface. True False
Answer
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23 Some animals can see beyond the visible light spectrum to see UV or infrared rays. True False
Answer
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24 Which type of EM waves can be detected as heat by thermal imaging cameras? A Infrared B Red C Ultraviolet D Violet
Answer
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SLIDE 25 X-Rays
X-rays (ray is short for radiation) are electromagnetic waves that have wavelengths ranging from 0.01 to 10 nm, which are shorter than Ultraviolet Light, but longer than Gamma rays. X-rays were discovered by Wilhelm Rontgen, and are called "X"-rays due to his use
- f the letter "Z" to signify
another unknown type of radiation. X-rays are emitted by electrons and have high energy levels which allow them to be used in the medical field for imaging.
Slide 73 / 121 Gamma Rays
Gamma rays are the type of electromagnetic radiation with the highest amount of energy. They have the shortest wavelength, and therefore the highest frequency. Gamma rays and X-rays are both so high energy they can ionize atoms - that means they can violently rip electrons away from atoms - which makes them dangerous. Gamma rays were discovered in 1900 by Paul Villard and were later named "Gamma" rays by Ernest Rutherford (also credited with discovering the nucleus of an atom.) Gamma rays are produced by the high energy decay of the atomic nucleus.
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Gamma radiation has been used in medical procedures overseen by Medical Physicsts called Radiosurgery. In Radiosurgery a "Gamma Knife" uses over 200 sources of gamma radiation from the chemical element Cobalt to converge on brain tumors smaller than 4 cm without the patient undergoing
- surgery. The procedure has been
effective in killing the tumors with few complications.
Gamma Radiation in the Medical Field Slide 75 / 121
SLIDE 26
The Cyber Knife uses a robotic arm (for accuracy) and gamma radation to kill tumors.
Gamma Radiation in the Medical Field Slide 76 / 121
25 The highest energy electromagnetic waves are A Microwaves B Ultraviolet C X-rays D Gamma rays
Answer
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26 Which of the following gives the correct order of EM waves from lowest energy to highest energy? A Radio, infrared, microwaves, green light, gamma rays, X-rays B Gamma rays, ultraviolet, red light, infrared, radio waves, microwaves C Microwaves, infrared, green light, ultraviolet, X-rays, Gamma rays D Radio, ultraviolet, red light, infrared, Gamma rays, X- rays.
Answer
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SLIDE 27 27 Which type of high energy EM wave has been used by a physicist to kill cancer cells? A Ultraviolet B Infrared C X-ray D Gamma ray
Answer
Slide 79 / 121 Visible Light
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Visible Light is the region of the electromagnetic spectrum humans can see. As previously mentioned, the colors we see depend upon the wavelength and frequency of the light. Visible light waves, like all electromagnetic waves, travel through space until they hit an
- bject and are either reflected,
absorbed, or transmitted.
Click here to watch Bill Nye explain the nature of colored light.
Visible Light Slide 81 / 121
SLIDE 28 Colors We Can See
While visible light is made up of many colors, the human eye can only distinguish the three primary colors: red, green, and blue. When two primary colors are added together, additional colors are created, called secondary colors. Red + Green = Yellow Red + Blue = Magenta Blue + Green = Cyan When all three primary colors are added together, white light is produced. Click Here to see a Phet simulation on color mixing
Slide 82 / 121 Why Do Objects Have Color?
Objects appear to have certain colors due to light that either reflects or transmits. Opaque objects do not allow light to pass through them. Opaque objects have inherent properties that cause them to absorb most wavelengths of light that hit them, and reflect select wavelengths of light. The reflected wavelength of light is the color we see. Transparent objects let light pass through, transmiting the color of light the eye sees. A banana is yellow because it is opaque. If white light shines on the banana, all wavelengths of light will be absorbed by the banana except yellow, which is reflected away and received by the eye.
Slide 83 / 121 Interactions With Matter
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SLIDE 29 Interactions with Matter
When electromagnetic waves collide with matter their direction of motion is altered resulting in three possibilities: Reflection: they can bounce back off the matter. Absorption: they can be absorbed by the matter. Refraction: they can pass through the matter at a different angle.
Slide 85 / 121 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, the angle of reflection, that it hit the surface with, the angle of incidence. Reflection: angle of incidence = angle of reflection
Slide 86 / 121 Types of Reflection
There are two types of Reflection that light can undergo depending on the surface that light hits: Specular Reflection Diffuse Reflection
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SLIDE 30 Specular Reflection
Specular Reflection occurs when the object the light is bouncing off of is flat. All of the incident rays come in parallel to each other. Since all of the rays have the same incident angle, all of the reflected rays have the same reflected angle. This results in a high intensity
- f the reflected light at a
particular point.
Slide 88 / 121 Diffuse Reflection
Diffuse Reflection occurs when the object that the light is bouncing off of is not flat, causing light waves to reflect at various angles. All of the incident rays come in parallel to each other, but because they do not all hit the object at the same angle, the reflected rays are at different angles to each other. This results in reduced intensity of reflected light at any particular point.
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Absorption of Light
When light is incident on an opaque material, some of the light is absorbed and some light is reflected based on inherent properties
- f the object (what type of atoms it is made up of and how they are
arranged). White objects will reflect all colors of light since white light contains all colors of the spectrum. This why all projection screens are white! Black objects will absorb all colors of light since black is the absence of light.
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SLIDE 31 28 Which of the following colors reflects off a violet,
A red B orange C green D violet
Answer
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29 Which of the following colors reflects off a basketball? A red B orange C yellow D green
Answer
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30 If an object hit by white light appears green, which of the following colors of light must be absorbed by the
A red B orange C yellow D all of the above
Answer
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SLIDE 32 What Happens to the Absorbed Light?
Remember that light is
absorbs light it is absorbing energy, which causes the total internal energy of the material to increase. Eventually the
- bject will emit the thermal
energy in the form of infrared radiation. In other words, the more light that is absorbed by an opaque
- bject, the hotter it gets!
In the sun, which feels hotter, wearing a white shirt or a black shirt?
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31 Which shirt will get hotter in the sun due to its color? A Red B Blue C Orange D They will all get the same temperature
Answer
Slide 95 / 121 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. Objects with longer wavelengths are affected the least. In the picture above, which light appears to bend the least? Note, the frequency of the light does not change, only the wavelength and wave speed.
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SLIDE 33 Refraction
When electromagnetic radiation interacts with a transparent material, some of the light will reflect (as it does with an opaque
- bject) but most of the light will refract.
Refraction is the bending of light as it goes from one material to another due to the differences in densities of the two materials. This what makes the paintbrush in the picture look like it is shifted over.
Slide 97 / 121 How Refraction Works
When light passes through transparent material that is more dense than the material it is coming from, the speed of the light decreases. The light hits the new material at what is called the angle of incidence. The angle of incidence is measured from the "normal" - an imaginary line perpendicular to the surface of the material. Notice the refracted light bends at a steeper angle relative to the normal. If you measure the angle of refraction from the normal is it the same as, less than, or greater than the angle
- f incidence in this picture?
Slide 98 / 121 Light Reflects and Refracts
When light comes into contact with the boundary between two materials, some of the light will reflect while the rest refracts. Because of this, refracted light is less intense than incident light, but more intense than the reflected light.
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SLIDE 34 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 closer than they actually are. The more perpendicular the view of the object located underwater, the more accurately you will see its position because the amount of refraction will decrease.
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Viewing From Directly Above
Incident light will refract if it passes through a transparent object and is directed at an angle to the object. If the light is incident perpendicularly then the light will not refract.
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32 When light hits a transparent boundary, its frequency changes dues to changing speed. True False
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SLIDE 35
33 When light hits a transparent boundary, its wavelength changes dues to changing speed. True False
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34 When light travels from a less dense medium like air to a denser medium like oil, its speed A Increases B Decreases C Stays the same
Answer
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35 When light travels from water to air its speed A Increases B Decreases C Stays the same
Answer
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SLIDE 36
36 Waves with longer wavelengths have a ________ angle of refraction than waves with shorter wavelengths. A Larger B Smaller C The same as
Answer
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37 Which of the following waves in the visible light spectrum bends the most when it is refracted? A Red B Orange C Yellow
Answer
D Green
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38 Based on the diagram below, how will light bend as it passes from air to water? A Away from the normal B Towards the normal C It won't change its path
Answer
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SLIDE 37 39 If light passes from air to water at an incident angle
- f 45 degrees, which of the following angles is a
possible angle of refraction? A 0 degrees B 30 degrees C 45 degrees D 60 degrees
Answer
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40 If light passes from water to air at an incident angle
- f 45 degrees, which of the following angles is a
possible angle of refraction? A 0 degrees B 30 degrees C 45 degrees D 60 degrees
Answer
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41 If light passes from water to air at an incident angle
- f 45, which of the following angles is a possible
angle of reflection? A 0 B 30 C 45 D 90
Answer
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SLIDE 38 42 If light passes from air to water at an incident angle
- f 90 degrees, which of the following will occur?
A light will refract towards the normal B light will refract away from the normal C light will not refract
Answer
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43 Light is incident to a block of glass at an angle as
- shown. As light passes through the glass and back
into air, which path is the correct path of the light? A B C
A B C
Answer
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44 What happens to the intensity of light as it refracts through a transparent material? A it increases B it decreases C it stays the same
Answer
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SLIDE 39 Rainbows
Rainbows are created when white light from the sun passes through water molecules in the air. Light is bent inside the water molecule as it slows down. When the light hits the back end
- f the rain drop it reflects and is
transmitted into the air.
Slide 115 / 121 Rainbows
This transmitted reflected light is what we see as a rainbow. The colors of a rainbow are in the order of the visible spectrum with red on top and violet on the bottom.
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Capturing Images
The characterics of light have allowed us to permanently capture images. Photography has taken off from a somewhat dangerous technique to a ubiquitous mode of expression. 1827 - A silver-coated copper plate was treated with chemicals that enabled it to capture light radiation and dangerous chemicals were used to "fix" the image into the plating. 2014 - A dog captures a permanent image known as a "selfie" using a digital camera phone.
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SLIDE 40 Capturing Images
How images are captured in digital cameras.
- 1. Light reflects off the object being photographed.
- 2. This light reflects off the object in all different directions and
hits the lens from different angles.
- 3. The lens focuses these rays of light to a point behind the
focal point forming a real image.
- 4. The real image is captured when the light hits sensors that
convert the light to electrical charges of varying magnitude depending on the brightness and color of the light hitting each sensor.
- 5. The computer in the camera takes the grid of electrical
charges and converts them into a picture.
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Capturing X-ray Images
X-rays are higher energy than light waves. The X-rays pass right through less dense material like soft tissues, but are absorbed by denser material like bones. X-rays are sent through the body part of interest to a film detector
- r sensor behind it. The X-rays that pass through soft tissues are
exposed as dark areas on the detector. The X-rays that are absorbed by dense tissues do not pass through, leaving those areas white on the sensor.
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SLIDE 41
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