What is Electromagnetic Radiation? The Electromagnetic Spectrum - - PDF document

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8th Grade

Electromagnetic Radiation

2015-10-23 www.njctl.org

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· Interactions with Matter · What is Electromagnetic Radiation? · The Electromagnetic Spectrum

Click on the topic to go to that section

· Examples of Light Interactions with Matter

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What is Electromagnetic Radiation?

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Slide 5 / 147 Electromagnetic Radiation

What do X-rays, light, microwaves, radio waves, and infrared have in common? Click in the box to see the answer. They are all types of electromagnetic radiation.

Slide 6 / 147 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 / 147 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. We are constantly bombarded by electromagnetic radiation, most of which we cannot see.

Slide 8 / 147 Electromagnetic Radiation

Not all electromagnetic radiation we interact with is bad. When you cook food in a microwave, listen to music, see colors, or feel heat, you are experiencing electromagnetic radiation. How do you think electromagnetic radiation travels through space?

Slide 9 / 147 Electromagnetic Radiation

One way electromagnetic radiation travels through space is as a wave. What's "waving" in an electromagnetic wave? Electromagnetic waves are different from mechanical waves because they don't need a medium to travel through.

Slide 10 / 147 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.

Slide 11 / 147 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! Electromagnetic waves also do not lose energy as they travel. This is unlike mechanical transverse waves which lose some of 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 12 / 147 Electromagnetic Wave Characteristics

Electromagnetic waves have the same wave characteristics we studied last unit: wavelength (λ) 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? Hint: Not this!

Slide 13 / 147 The Vacuum of Empty Space

A vacuum is a space that is completely empty and contains 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 14 / 147 Speed of Electromagnetic Radiation

Scientists use the idea of constant speed (c) in a vacuum because it's useful for

• calculations. c is also referred to as the speed
• f light.

In theory, nothing can travel faster than the speed of light. In reality, electromagnetic waves slow down when encountering any matter. If you could travel at the speed of light, you could go around Earth's equator 7.5 times in one second.

Slide 15 / 147 Wavelength of Electromagnetic Radiation

Different types of electromagnetic radiation have different wavelengths. Drag and drop the terms into the correct place on the wave. wavelength crest trough

Slide 15 (Answer) / 147 Wavelength of Electromagnetic Radiation

Different types of electromagnetic radiation have different wavelengths. Drag and drop the terms into the correct place on the wave. wavelength crest trough

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Answer

Slide 16 / 147 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? Click in the box to see the answer. As one value goes up, the other goes down. For example, the longer the wavelength, the lower the frequency.

Slide 17 / 147 Speed, Wavelength and Frequency

A wave's frequency or wavelength can be solved for using the wave equation from last unit: Since all electromagnetic radiation travels at the speed of light, v can be replaced with this value every time, represented by the letter c, which equals 300,000,000 m/s.

Slide 18 / 147 Speed, Wavelength and Frequency

We use the new wave equation to solve for the frequency or wavelength of electromagnetic waves based on the equations below:

• r

Click here to watch a video that proves the speed of light by 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 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

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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 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

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Answer

1.19 s

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2 The Sun is 149,600,000 km away from Earth. How many minutes ago did the radiation that is hitting you right now leave the Sun? c = 300,000,000 m/s

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2 The Sun is 149,600,000 km away from Earth. How many minutes ago did the radiation that is hitting you right now leave the Sun? c = 300,000,000 m/s

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Answer

*Remember to convert 149,600,00 km to 149,600,000,000 m. t = 498.67 sec

• r about 8 minutes

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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

• ver the Empire State Building (381 m)?

c = 300,000,000 m/s

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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

• ver the Empire State Building (381 m)?

c = 300,000,000 m/s

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Answer

556 m; Yes

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4 What is the frequency of a radio wave that has a wavelength of 1 cm (0.01 m)?

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4 What is the frequency of a radio wave that has a wavelength of 1 cm (0.01 m)?

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Answer

3.0 x 10

10 Hz

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5 An electromagnetic wave has a frequency of 1.5 GHz (1,500,000,000 Hz). What is the wavelength of the wave? (1 GHz = 1,000,000,000 Hz)

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5 An electromagnetic wave has a frequency of 1.5 GHz (1,500,000,000 Hz). What is the wavelength of the wave? (1 GHz = 1,000,000,000 Hz)

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Answer

0.2 m

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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?

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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?

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Answer

6.5 x 10

• 7 Hz

(0.00000065 Hz)

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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

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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

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Answer

D

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8 Which of the following frequencies would have the shortest wavelength? A 1000 Hz B 100 Hz C 10 Hz D 1 Hz

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8 Which of the following frequencies would have the shortest wavelength? A 1000 Hz B 100 Hz C 10 Hz D 1 Hz

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Answer

A

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The Electromagnetic Spectrum

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Slide 28 / 147 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

Source: NASA

Note

Slide 29 / 147 The Electromagnetic Spectrum

The different types of electromagnetic waves that make up the spectrum are from left to right: Radio Microwave Infrared Visible Light Ultraviolet X-ray Gamma ray Longest wavelength Shortest wavelength Think about the relationship between wavelength and frequency. How will frequency change as you go from Radio waves to Gamma Rays?

Slide 29 (Answer) / 147 The Electromagnetic Spectrum

The different types of electromagnetic waves that make up the spectrum are from left to right: Radio Microwave Infrared Visible Light Ultraviolet X-ray Gamma ray Longest wavelength Shortest wavelength Think about the relationship between wavelength and frequency. How will frequency change as you go from Radio waves to Gamma Rays?

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Answer Wavelength and frequency are inverse to each other. If wavelength decreases from radio waves to gamma rays, then frequency will increase from radio waves to gamma rays.

Slide 30 / 147 Energy Differences

The higher the frequency, the higher the energy.

Increasing frequency Increasing energy Increasing wavelength

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

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

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Answer

B

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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

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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

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Answer

A

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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

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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

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Answer

D

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

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

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Answer

A

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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

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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

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Answer

C

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

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

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Answer

B

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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

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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

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Answer

D

Slide 38 / 147 Radio Waves

Radio waves were first mathematically theorized to exist by James Clark Maxwell in 1864. They were not actually discovered until 1888 by Heinrich Hertz. Hertz experimentally determined the electromagnetic waves he produced in a laboratory had different wavelengths than light, but reflected and refracted in the same manner.

Slide 39 / 147 Radio Waves

Since radio 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! Radio waves have the longest wavelengths of all electromagnetic

• waves. The wavelength of a radio wave measures anywhere from

approximately 20 cm to the diameter of Earth.

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A radio needs two parts: a transmitter and a receiver.

How We Hear Radio Waves Slide 41 / 147

The transmitter encodes information onto a wave by changing a property of the wave. It then sends the wave out through an antenna.

How We Hear Radio Waves Slide 42 / 147

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.

How We Hear Radio Waves

The mechanical wave is amplified with an amplifier and vibrates speakers accordingly.

Slide 43 / 147 AM vs FM Radio

AM (Amplitude Modulation) FM (Frequency Modulation) There are two ways to change the property of the wave that is sent out by the transmitter.

Slide 44 / 147 AM Radios

AM (Amplitude Modulation)

• ccurs when the amplitude

(height) of the wave is changed. When the receiver detects the signal, it is decoding the change in the amplitude of the waves that were transmitted.

Slide 45 / 147 FM Radios

FM (Frequency Modulation) occurs when the frequency of the wave is changed. When the receiver detects the signal, it is decoding the change in the frequency of the waves that were transmitted.

Slide 46 / 147 Why does FM radio sound clearer?

Both AM and FM waves undergo slight changes in amplitude as they travel. Since AM stations send information by changing amplitude, each additional change in amplitude is heard as static. Since FM stations send information by changing frequency, the radio simply filters out any changes in amplitude. This leads to a clear station with no static.

Slide 47 / 147 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.

Slide 48 / 147 How TVs use radio waves

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

• ut through coaxial cables or light pulses, which are used in fiber
• ptics.

Slide 49 / 147 Radio Waves from Outer Space

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. Objects in space like stars and galaxies emit radio waves.

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16 Radio waves carry the lowest energy of any electromagnetic wave because they have the smallest wavelength. True False

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16 Radio waves carry the lowest energy of any electromagnetic wave because they have the smallest wavelength. True False

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Answer

False

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17 What is used to decode radio waves? A amplifier B transmitter C receiver D antenna

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17 What is used to decode radio waves? A amplifier B transmitter C receiver D antenna

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Answer

C

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18 FM radio waves are transmitted by modifying the wave’s A speed B frequency C wavelength D amplitude

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18 FM radio waves are transmitted by modifying the wave’s A speed B frequency C wavelength D amplitude

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Answer

B

Slide 53 / 147 Microwaves

Microwaves are a form of electromagnetic radiation that have shorter wavelengths than radio waves. This is why they have the name "micro". The wavelengths of microwaves range from 1 mm to 1 m. Since Microwaves have shorter wavelengths and higher frequencies, they can carry more energy than radio waves. Microwaves are used for: Communications Radar Navigation Heating Radio Astronomy

Slide 54 / 147 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 cell phones 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.

Slide 55 / 147 Microwaves Used In Communications

Due to microwave technology, other devices such as bluetooth and WiFi work at a frequency of around 2.5 GHz. Next time you post an image, be sure to thank microwaves for making Instagram possible!

Slide 56 / 147 Slide 57 / 147 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 58 / 147 Microwaves used in Heating

Microwave Ovens were actually discovered by 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.

Slide 59 / 147 Microwaves used in Heating

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

• ther parts of the food, causing

the food to heat up.

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19 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 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.

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19 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 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.

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Answer

C

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20 Which type of electromagnetic wave is used to transmit cell phone signals? A Radio waves B TV waves C Microwaves D Gamma rays

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20 Which type of electromagnetic wave is used to transmit cell phone signals? A Radio waves B TV waves C Microwaves D Gamma rays

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Answer

C

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21 Why do microwaves have higher data transmission rates than radio waves? 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.

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21 Why do microwaves have higher data transmission rates than radio waves? 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.

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Answer

B

Slide 63 / 147 Mid-Range Electromagnetic Waves

In the middle region of the electromagnetic spectrum, waves have shorter wavelengths, higher frequencies and higher energy than radio waves. Infrared Visible Light Ultraviolet There are three types of light that make up this mid- range region:

Slide 64 / 147 Infrared Light

Infrared light has the longest wavelengths of any mid-range wave. It therefore has 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.

Slide 65 / 147 Infrared 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 66 / 147 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.

Click here to see how Herschel discovered infrared radiation

Slide 67 / 147 Infrared Radiation as Heat

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.

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Infrared radiation is emitted 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 Slide 69 / 147 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 70 / 147 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.

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The colors we see depend upon the wavelength and frequency of the light.

Click here to watch Bill Nye explain the nature of colored light.

Visible Light

Visible light waves, like all electromagnetic waves, travel through space until they hit an object and are either reflected, absorbed, or transmitted.

Slide 72 / 147 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 absorb certain wavelengths of light and transmits other wavelengths. The wavelengths of light absorbed are determined by the object's pigments.The light that is transmitted is the color of light the eye sees.

Slide 73 / 147 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.

Slide 74 / 147 Wavelengths of Visible Light

The portion of the electromagnetic spectrum that human eyes can see is actually very

• small. Visible light

has wavelengths that measure between 400 nm (violet) to 700 nm (red)*. *A nanometer (nm) is equal to 1x10-9 meters or 0.000000001 meters

Slide 75 / 147 Wavelengths of Visible Light

This means that violet light has a frequency almost twice as large as red light, and, therefore, almost twice as much energy.

Slide 76 / 147 Brightness of Visible Light

The brightness of visible light that we see is dependent on the light wave's amplitude. Which light wave below has the higher amplitude? Which light wave do you think will appear brighter? The top light wave has a higher amplitude. The top light wave also will appear brighter.

Slide 77 / 147 Ultraviolet Radiation

Ultraviolet radiation is a form

• f electromagnetic radiation

that has a shorter wavelength than visible light and is therefore undetectable by the human eye. However, some birds and insects can see some wavelengths in the UV range. The range of UV wavelength is 400 nm down to 10 nm. The right side shows what birds with UV perception can see. Click the image for more examples

Slide 78 / 147 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. The intensity of UVB rays 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

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Ultraviolet C (UVC) waves have a wavelength between 280 nm and 100 nm. Most UVC rays are absorbed by Earth's atmosphere and do not reach the surface of Earth.

Types of UV Radiation - UVC Slide 81 / 147 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 82 / 147 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.

Slide 83 / 147 Protection from UV Radiation

Someone using a sunscreen with an SPF

• f 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%. Sunburn peeling from not using sunscreen.

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22 Humans can see which of the following types of mid-range electromagnetic waves: A Infrared B Visible Light C Ultraviolet Light D All of the above

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22 Humans can see which of the following types of mid-range electromagnetic waves: A Infrared B Visible Light C Ultraviolet Light D All of the above

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Answer

B

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23 Within the mid-range region of the EM Spectrum, _________ light has the longest wavelength. A Infrared B Red C Ultraviolet D Violet

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23 Within the mid-range region of the EM Spectrum, _________ light has the longest wavelength. A Infrared B Red C Ultraviolet D Violet

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Answer

A

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24 Which type of visible light has the highest energy? A Red B Orange C Green D Violet

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24 Which type of visible light has the highest energy? A Red B Orange C Green D Violet

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Answer

D

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25 The brightness of a light wave is related to the wave’s amplitude. True False

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25 The brightness of a light wave is related to the wave’s amplitude. True False

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Answer

True

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26 UV rays cannot penetrate clouds to reach Earth's surface. True False

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26 UV rays cannot penetrate clouds to reach Earth's surface. True False

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Answer

False

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27 Some animals can see beyond the visible light spectrum to see UV or infrared rays. True False

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27 Some animals can see beyond the visible light spectrum to see UV or infrared rays. True False

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Answer

True

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28 Which type of EM waves can be detected as heat by thermal imaging cameras? A Infrared B Red C Ultraviolet D Violet

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28 Which type of EM waves can be detected as heat by thermal imaging cameras? A Infrared B Red C Ultraviolet D Violet

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Answer

A

Slide 91 / 147 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 92 / 147 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 can make them dangerous.

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Gamma radiation has been used in medical procedures, overseen by medical physicists, 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 94 / 147

The Cyber Knife uses a robotic arm (for accuracy) and gamma radiation to kill tumors.

Gamma Radiation in the Medical Field Slide 95 / 147

29 The highest energy electromagnetic waves are A Microwaves B Ultraviolet C X-rays D Gamma rays

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29 The highest energy electromagnetic waves are A Microwaves B Ultraviolet C X-rays D Gamma rays

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Answer

D

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30 Which of the following lists electromagnetic 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.

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30 Which of the following lists electromagnetic 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.

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Answer

C

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31 Which type of high energy EM wave has been used by physicists to kill cancer cells? A Ultraviolet B Infrared C X-ray D Gamma ray

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31 Which type of high energy EM wave has been used by physicists to kill cancer cells? A Ultraviolet B Infrared C X-ray D Gamma ray

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Answer

D

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Interactions With Matter

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Slide 99 / 147 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?

Slide 100 / 147 Interactions with Matter

Reflection: waves bounce back off the matter. Absorption: waves can be absorbed by the matter. Refraction: waves pass through the matter at a different angle due to the wave's change in speed. Note that the direction of electromagnetic (light) waves can be traced as straight-line rays.

Slide 101 / 147 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. Reflection: angle of incidence = angle of reflection

Slide 102 / 147 Types of Reflection

There are two types of reflection that light can undergo depending on the surface that the light hits: · Specular Reflection · Diffuse Reflection

Slide 103 / 147 Specular Reflection

Specular Reflection occurs when light bounces off a flat

• bject. All of the incident light

rays come in parallel to each

• ther.

Since all of the light rays have the same incident angle, all of the reflected rays have the same reflected angle. This results in a high intensity of the reflected light at a particular point and a clear reflected image.

Slide 104 / 147 Diffuse Reflection

Diffuse Reflection occurs when light bounces off a surface that is not flat, causing light waves to reflect at various angles. All of the incident rays come in parallel to each other. However, 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. The reflected image is blurry if any image is produced at all.

Slide 105 / 147 Specular versus Diffuse Reflection

What kind of reflection do you think is represented by the image below? Why? Diffuse! Even though we see a reflection of the sun, it is blurry. This is because the surface of the ocean is rough and the reflected light rays are not all parallel to each other.

Slide 106 / 147 Absorption of Light

When light is incident on an opaque material, some of the light is absorbed and some light is reflected. The wavelength of light that is absorbed or reflected depends on: · inherent properties of the object (what type of atoms it is made up of and how they are arranged) · the frequency and wavelength of the incident light 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.

Slide 107 / 147 Absorption of Light

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

Slide 108 / 147 What happens to the absorbed light?

Remember that light is

• energy. When an object

absorbs light it is absorbing energy, which causes the total internal energy of the material to increase. Eventually the object will emit the thermal energy in the form

• f infrared radiation.

In other words, the more light that is absorbed by an opaque

• bject, the hotter it gets!

When you are standing in the sun, which feels hotter: wearing a white shirt or a black shirt?

Slide 109 / 147

32 Which of the following colors reflects off a violet, opaque

• bject?

A red B orange C green D violet

Slide 109 (Answer) / 147

32 Which of the following colors reflects off a violet, opaque

• bject?

A red B orange C green D violet

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Answer

D

Slide 110 / 147

33 Which of the following colors reflects off a basketball? A red B orange C yellow D green

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33 Which of the following colors reflects off a basketball? A red B orange C yellow D green

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Answer

B

Slide 111 / 147

34 If an object hit by white light appears green, which of the following colors of light must be absorbed by the object? A red B orange C yellow D all of the above

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34 If an object hit by white light appears green, which of the following colors of light must be absorbed by the object? A red B orange C yellow D all of the above

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Answer

D

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35 An opaque white object can never appear green. True False

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35 An opaque white object can never appear green. True False

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Answer

False- it can appear green if the incident light is green.

Slide 113 / 147

36 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.

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36 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.

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Answer

B

Slide 114 / 147 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.

Slide 115 / 147 Separating White Light

Colors with longer wavelengths are affected the least when going through a prism. Note: The frequency of light does not change, only the speed and wavelength changes. In the picture below, which color of visible light appears to bend the least?

Slide 116 / 147 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 material with a different density. The difference in density causes the light to change speed and "bend".

Slide 117 / 147 How Refraction Works

When light passes into a denser medium, 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. The normal is indicated by

the red line in the diagram to the right.

Slide 118 / 147 How Refraction Works

Notice that as the light enters the denser material, the refracted light bends towards the normal. If you measure the angle of refraction from the normal, is it the same as, less than, or greater than the angle of incidence in this picture?

Slide 119 / 147 How Refraction Works

When light passes into a less dense medium, it speeds up. Notice that as the light enters the less dense material, the refracted light bends away from the normal. If you measure the angle of refraction from the normal, is it the same as, less than, or greater than the angle of incidence in this picture?

Slide 120 / 147 Light Reflects and Refracts

When light comes into contact with the boundary between two transparent materials, some of the light will reflect while the rest refracts. Because of this, refracted light is: · less intense than the original incident light · but more intense than the reflected light.

Slide 121 / 147 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.

Slide 122 / 147 Viewing From Directly Above

Incident light will refract if it passes through a transparent object and is directed at an angle to the object. However, if the incident light is perpendicular to the boundary between mediums, then the light will not refract.

Slide 123 / 147

37 When light hits a transparent boundary, its frequency changes due to changing speed. True False

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37 When light hits a transparent boundary, its frequency changes due to changing speed. True False

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Answer

False

Slide 124 / 147

38 When light hits a transparent boundary, its wavelength changes due to changing speed. True False

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38 When light hits a transparent boundary, its wavelength changes due to changing speed. True False

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Answer

True

Slide 125 / 147

39 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

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39 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

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Answer

B

Slide 126 / 147

40 When light travels from water to air its speed A increases. B decreases. C stays the same.

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40 When light travels from water to air its speed A increases. B decreases. C stays the same.

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Answer

A

Slide 127 / 147

41 Waves with longer wavelengths have a ________ angle

• f refraction than waves with shorter wavelengths.

A larger B smaller C the same as

Slide 127 (Answer) / 147

41 Waves with longer wavelengths have a ________ angle

• f refraction than waves with shorter wavelengths.

A larger B smaller C the same as

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Answer

B

Slide 128 / 147

42 Which of the following waves in the visible light spectrum bends the most when it is refracted? A Red B Orange C Yellow D Green

Slide 128 (Answer) / 147

42 Which of the following waves in the visible light spectrum bends the most when it is refracted? A Red B Orange C Yellow D Green

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Answer

D

Slide 129 / 147

43 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

Slide 129 (Answer) / 147

43 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

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Answer

B

Slide 130 / 147

44 If light passes from air to water at an incident angle of 45 degrees, which of the following angles is a possible angle

• f refraction?

A 0 degrees B 30 degrees C 45 degrees D 60 degrees

Slide 130 (Answer) / 147

44 If light passes from air to water at an incident angle of 45 degrees, which of the following angles is a possible angle

• f refraction?

A 0 degrees B 30 degrees C 45 degrees D 60 degrees

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Answer

B

Slide 131 / 147

45 If light passes from water to air at an incident angle of 45 degrees, which of the following angles is a possible angle

• f refraction?

A 0 degrees B 30 degrees C 45 degrees D 60 degrees

Slide 131 (Answer) / 147

45 If light passes from water to air at an incident angle of 45 degrees, which of the following angles is a possible angle

• f refraction?

A 0 degrees B 30 degrees C 45 degrees D 60 degrees

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Answer

D

Slide 132 / 147

46 If light passes from water to air at an incident angle of 45, which of the following angles is a possible angle of reflection? A 0 degrees B 30 degrees C 45 degrees D 90 degrees

Slide 132 (Answer) / 147

46 If light passes from water to air at an incident angle of 45, which of the following angles is a possible angle of reflection? A 0 degrees B 30 degrees C 45 degrees D 90 degrees

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Answer

C

Slide 133 / 147

47 If light passes from air to water at an incident angle of 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

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47 If light passes from air to water at an incident angle of 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

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Answer

C

Slide 134 / 147

48 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

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48 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

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Answer

A

Slide 135 / 147

49 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.

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49 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.

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Answer

B

Slide 136 / 147

Examples of Light Interactions with Matter

Return to Table

• f Contents

Slide 137 / 147 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. Do you remember why it slows down? When the light hits the back end of the rain drop, it reflects and is transmitted into the air. Does the light bend again as it leaves the rain drop? Why?

Slide 138 / 147 Rainbows

Sunlight that enters a raindrop, reflects internally and then refracts out of the rain drop 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. Do you recall why sunlight is separated out into individual colors? Because colored light waves have different wavelengths, they bend at different angles, creating a spectrum of color. Colors with shorter wavelengths (higher frequencies) bend the most and vice versa.

Slide 139 / 147 Capturing X-ray Images

X-rays are higher energy than light

• waves. Because of

this, X-rays pass right through less dense material like soft tissues, but are absorbed by denser material like bones.

Slide 140 / 147 Capturing X-ray Images

X-rays are sent through the body part of interest to a film detector or sensor behind it. The X-rays that pass through soft tissues are exposed as dark areas

• n the detector.

The X-rays that are absorbed by dense tissues (or metals) do not pass through, leaving those areas white on the sensor.

Slide 141 / 147 Capturing Images

The characteristics of light have allowed us to permanently capture images. Photography has taken off from a somewhat dangerous technique to an everyday 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.

Slide 142 / 147 How Images are Captured with Digital Cameras

• 1. Light reflects off the object being photographed and

hits the lens from different angles.

• 2. Due to refraction, the lens focuses these rays to a specific

point forming an image.

• 3. The image is converted into electrical charges when the

light hits the camera sensors. These electrical charges have different strengths depending on the brightness and color of the light hitting each sensor.

• 4. The computer in the camera takes the grid of electrical

charges and converts them into a picture.

Slide 143 / 147 Slide 144 / 147

50 What is the minimum amount of times light needs to be refracted in a rain drop in order to see a rainbow? A 1 B 2 C 3 D 4

Slide 144 (Answer) / 147

50 What is the minimum amount of times light needs to be refracted in a rain drop in order to see a rainbow? A 1 B 2 C 3 D 4

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Answer

B

Slide 145 / 147

51 X-rays have a higher frequency and lower wavelength than visible light waves. True False

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51 X-rays have a higher frequency and lower wavelength than visible light waves. True False

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Answer

True

Slide 146 / 147

52 X-rays pass through bones and soft tissue leaving a white area on a sensor. True False

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52 X-rays pass through bones and soft tissue leaving a white area on a sensor. True False

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Answer

False

Slide 147 / 147

53 What is involved when capturing an image on a digital camera? Choose all that apply. A visible light B UV rays C reflection D refraction

Slide 147 (Answer) / 147

53 What is involved when capturing an image on a digital camera? Choose all that apply. A visible light B UV rays C reflection D refraction

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Answer

A, C and D