Name: _______________________________ 1 Science 30 Unit C – Electromagnetic Energy Outcome 2: Students will describe the properties of the electromagnetic spectrum and their applications in medical technologies, communication systems and remote-sensing technologies used to study the universe. Specific Outcome 2.1: Describe the range of the electromagnetic spectrum form long, low- frequency radio waves through microwaves, infrared (IR) rays, visible light rays and ultraviolet (UV) radiation to very short, high-frequency waves such as X-rays and gamma rays. Specific Outcome 2.6: Investigate and describe the relationships of the variables in the universal wave equation = Specific Outcome 2.2: Compare and contrast, to each other, the various constituents of the electromagnetic spectrum, on the basis of source, frequency, wavelength and energy, and their effect on living tissue. Textbook reference pages: p. 410 – 434 in Science 30 Radiation is energy emitted in the form of particles or waves. Energy travels from the Sun to Earth in the form of radiation Electromagnetic radiation (EMR) is a transfer of energy; it is a wave that consists of a changing electric field and a changing magnetic field travelling at right angles to one another. EMR PRODUCTION All forms of EMR are produced by accelerating electric charges In outcome 1, we learned that electric fields are produced by charged objects and magnetic fields are produced by moving charges. Visible light & radio waves are produced by electrons dropping to lower energy levels in atoms or vibrating electrons in special circuits
Transcript
Name: _______________________________
1
Science 30
Unit C – Electromagnetic Energy
Outcome 2: Students will describe the properties of the electromagnetic spectrum and their
applications in medical technologies, communication systems and remote-sensing technologies
used to study the universe.
Specific Outcome 2.1: Describe the range of the electromagnetic spectrum form long, low-
frequency radio waves through microwaves, infrared (IR) rays, visible light rays and ultraviolet
(UV) radiation to very short, high-frequency waves such as X-rays and gamma rays.
Specific Outcome 2.6: Investigate and describe the relationships of the variables in the
universal wave equation 𝑣 = 𝜆𝑓
Specific Outcome 2.2: Compare and contrast, to each other, the various constituents of the
electromagnetic spectrum, on the basis of source, frequency, wavelength and energy, and
their effect on living tissue.
Textbook reference pages: p. 410 – 434 in Science 30
Radiation is energy emitted in the form of particles or waves.
Energy travels from the Sun to Earth in the form of radiation
Electromagnetic radiation (EMR) is a transfer of energy; it is a wave that consists of a changing
electric field and a changing magnetic field travelling at right angles to one another.
EMR PRODUCTION
All forms of EMR are produced by accelerating electric charges
In outcome 1, we learned that electric fields are produced by charged objects and magnetic
fields are produced by moving charges.
Visible light & radio waves are produced by electrons dropping to lower energy levels in
atoms or vibrating electrons in special circuits
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ELECTROMAGNETIC RADIATION
Properties shared by all forms of EMR:
1. They all transfer energy from one place to another.
2. They all travel in transverse waves (not longitudinal)
Transverse waves: vibrations at right angles to wave direction
Longitudinal waves (Ex. Sound waves) – material vibrates in the same direction as the
wave motion.
3. EMR can travel through empty space (vacuum).
Other types of waves need some sort of medium to move
through:
o Water waves need liquid water
o Sound waves need some gas, liquid, or solid
material
4. EMR is made up electric and magnetic fields.
A changing magnetic field will produce an electric field and vice versa
The magnetic field is at right angles to the electric field
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5. All forms of EMR have the same speed of 3.00 x 108 m/s in
space (often abbreviated as 𝑐 found in your data
booklet).
6. EMR waves can all be reflected, refracted, diffracted
7. The shorter the wavelength (the higher the
frequency), the more dangerous the waves
are.
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DESCRIBING ELECTROMAGNETIC RADIATION
EMR is a transverse wave
All transverse waves have crests and troughs.
The wavelength is the distance of one cycle (crest
to crest for example)
o The wavelength is the distance from a point
on one wave to the same point on the next
wave.
o The symbol for wavelength is lamda, λ
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DETERMINING WAVELENGTH:
1. Determine the wavelength of this
EMR
2. Determine the wavelength of
the following TWO EMR.
FREQUENCY:
Frequency is the number of cycles that pass a certain point per second.
The symbol for frequency is 𝑓
Units for frequency = cycles per second = hertz (Hz)
Example: A frequency of 3 cycles per second = 3 Hz
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Examples:
1. The following diagram shows an illustration of an electromagnetic radiation passing a
detector. Use this information to determine the frequency of the EMR.
3. Determine the frequency of the following examples of electromagnetic radiation.
a. In 1.00ms, 740 radio waves pass the antenna of a radio.
b. In 1.00µs, 2450 microwaves pass through a point on a piece of cheese in a microwave
oven
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UNIVERSAL WAVE EQUATION
The measurement of wavelength and frequency not only describe key characteristics of
waves, they also provide a very convenient way to calculate the speed of a wave.
When talking about EMR travelling through a vacuum (like space), regardless of wavelength
or frequency, the speed will always be 3.00 x 108 m/s.
o This value is typically referred to as the speed of light and represented by letter 𝑐.
The universal wave can be represented:
c OR
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This may be helpful……
Examples:
1. An excited atom in a neon sign emits electromagnetic radiation with a wavelength of 6.4 x 10-
7 m.
a. Calculate the frequency of the electromagnetic radiation
b. If the neon sign was located 25.0 m from an observer, how long would it take the light
from the sign to reach the observer?
2. The antenna of a FM radio station broadcasts electromagnetic radiation with a frequency of
104.5 MHz. A driver in a car is receiving these FM radio waves while travelling down a highway
at 90.0 km/hr, or 25.0 m/s.
a. Calculate the wavelength of the electromagnetic radiation
b. Some of the FM radio waves can leave Earth’s atmosphere and travel into space.
Calculate how long it would take these radio waves to reach the Moon which is
located about 3.84 x 108 m from Earth.
c. Use your answer to part b. to determine how far the car would travel in the same time it
takes the radio wave to travel from Earth to the Moon.
Recall the formula for velocity:
v = 𝛥𝑑
𝛥𝑡
v = Velocity (m/s)
d = distance (m)
t = time (s)
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THE ELECTROMAGNETIC SPECTRUM
The electromagnetic spectrum is a continuous range of electromagnetic waves which are
emitted with specific characteristics and similar properties.
The electromagnetic spectrum is the wide band of different types of EMR ranging from radio
waves to gamma rays.
In order from lowest energy to highest: radio wave, microwave, infrared, visible, ultraviolet, x‐rays, gamma rays.
The energy content of EMR depends on two factors:
o Frequency (higher frequency means more energy)
o Intensity (“brightness”) (more waves means more energy)
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1. RADIO WAVES
Electromagnetic radiation used primarily for communications
produced from low-frequency vibrations of electrons
low energy
waves range in length from 106 m (long wave) to 10-4 m(short wave)
travel well in the atmosphere
lowest frequency of all electromagnetic radiation
effects of radio waves on living tissues depends on the frequency and wavelength
o it is unclear of the effect of radio waves emitted from the AC current in the
household and from power lines
o MRI (magnetic resonance imaging) used radio waves about 4 m in length
appear to have no harmful effects
Radio call signs are actually their frequencies. For example, 92.5 JOE FM means the
station is broadcasting using 92.5 MHz. (1MHz = 1000000 Hz) 630AM CHED Radio is
broadcasting using 630 KHz (1 KHz = 1000 Hz). Calculate the wavelength of the radio waves being emitted from:
a) JOE FM
v= fλ
λ = v/f
λ = 3.00 x 108 m/s ÷ 92.5 x 106 Hz
λ = 3.24 m
b) 630 CHED
v= fλ
λ = v/f
λ = 3.00 x 108 m/s ÷ 630 x 103 Hz
λ = 476 m
2. MICROWAVES
Electromagnetic radiation used primarily
for radar, satellite communication and
cooking food
High-frequency circuits are used to
produce microwaves of low frequency to
cook food
Higher-frequency microwaves are used in
telecommunications
o Can penetrate rain, snow, haze
and smoke
Transmit more energy than radio waves
waves range in length from 1m to 10-2 m
Microwaves cause water molecules to increase their molecular motion
Living tissue contains a high percentage of water so lower frequency microwaves can
be harmful for the tissue
Prolonged exposure to microwaves leads to cataracts
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3. INFRARED RADIATION
Electromagnetic radiation used primarily for communication and remote controls
Frequency between 3.0 1011 Hz and 4.3 1014 Hz
produced by the vibration or rotation of molecules in a materials
produces heating effects
waves range in length from 10-4 m to 10-6 m
can be detected by the nerve endings in the skin
Living tissue can be burned by infrared radiation
https://www.youtube.com/watch?v=2--0q0XlQJ0
4. VISIBLE LIGHT
Electromagnetic radiation used primarily for detecting colours
ROYGBIV
Frequency between 4.3 1014 Hz (red end) and 7.5 1014 Hz (violet end)
Red is lowest energy visible light whereas violet light has the highest energy
Emitted by objects that are hot
waves range in length from 700 nm (red end) to 400 nm (violet end)
light is transmitted in small bundles of electromagnetic energy called PHOTONS
Living tissue of plants is affected by visible light – all but green
o The chloroplasts absorb all light except green to facilitate the chemical reactions
of photosynthesis
When hit by light, the retina ejects electrons to form chemical reactions that lead to
sight
5. ULTRAVIOLET RADIATION
UV photons are emitted from very hot objects
Frequency between 7.5 1014 Hz and 1 1018 Hz
More energy than visible light
there are 3 types of ultraviolet radiation and each have a specific wave length
o UVA 400 nm to 315 nm
o UVB 315 nm to 280 nm
o UVC 280 nm to 100 nm
Effects on living tissues depends on the type of UV radiation
