2015.08.27.
ELECTROMAGNETIC WAVES
Edina Szabó-Meleg, PhD
Premed
.
WAVES (SUMMARY) I.
A wave can be described as a disturbance
that travels through a medium from one
location to another location.
The repeating and periodic disturbance
that moves through a medium from one
location to another is referred to as a
wave.
Categorization of waves
direction of movement of the particles of
the medium vs. direction of wave motion
Longitudinal waves
ability or inability to transmit
energy through a vacuum
Transverse waves
Mechanical
waves
Electromagnetic
waves
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WAVES (SUMMARY) II.
Longitudinal waves
Categorization of waves
Transverse waves
waves
(…according to direction of movement of the particles of the medium vs. direction of
wave motion)
wave is an energy transport phenomenon that transports energy along a medium without transporting matter
WAVES (SUMMARY) III.
Categorization of waves
Mechanical waves
require the presence of a medium
(e.g. sound waves)
Electromagnetic waves
can travel through the vacuum of outer
space
(e.g. light waves)
(…according to the ability to transmit energy through a vacuum)
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ELECTROMAGNETIC WAVES – GENERATION AND PROPAGATION
E
electric field
strength vector
x
x
magnetic field
strength vector
B
E
B
x
B
CHARACTERISTICS OF EM WAVES
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PROBLEM SOLVING
Consider the diagram below in order to answer questions #1-2.
1. The wavelength of the wave in the diagram above is given by letter ______.
2. The amplitude of the wave in the diagram above is given by letter _____.
PROBLEM SOLVING
Indicate the interval that represents one full wavelength.
a.
A to C
b.
B to D
c.
A to G
d.
C to G
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PROBLEM SOLVING
A wave is introduced into a thin wire held tight at each end. It has
an amplitude of 3.8 cm, a frequency of 51.2 Hz and a distance
from a crest to the neighboring trough of 12.8 cm.
Determine the period of such a wave.
PROBLEM SOLVING
A tennis coach paces back and forth along the sideline 10 times in
2 minutes. The frequency of her pacing is ________ Hz.
a. 5.0
b. 0.20
c. 0.12
d. 0.083
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PROBLEM SOLVING
A period of 5.0 seconds corresponds to a frequency of ________
Hertz.
a. 0.2
d. 0.05
b. 0.5
e. 0.002
c. 0.02
PROBLEM SOLVING
As the frequency of a wave increases, the period of the wave
___________.
a. decreases
b. increases
c. remains the same
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LIGHT
Has wave and particle nature
Reflection
Refraction
Diffraction
Interference
Polarization
Light wave:
electromagnetic wave
transverse wave – different from other waves
SPEED OF ELECTROMAGNETIC WAVES
• a wave or particle nature
↓
frequency and wavelength
𝑐 = 𝜆𝑓
In vacuum: speed of light (3 × 108 m/s).
In a medium : depend on the refractive index of the medium.
ELECTROMAGNETIC SPECTRUM WAVES
1.
2.
3.
4.
5.
6.
7.
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your radio…
your television…
your remote
control…
your
microwave
oven…
your text message…
the doctors’ X-ray…
CHARACTERISTICS OF ELECTROMAGNETIC SPECTRUM I.
DECREASING ENERGY
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CHARACTERISTICS OF ELECTROMAGNETIC SPECTRUM II.
THE VISIBLE LIGHT RANGE OF THE EM SPECTRUM I.
from 400 to 700 nm,
colors - wavelengths
ROY G . BIV
Red
Orange
Yellow
Green
Blue
Violet
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THE VISIBLE LIGHT RANGE OF THE EM SPECTRUM II.
from 400 to 700 nm,
center: 5.55x10-7 m = ? nm ←
calculation
Which color is the best perceived by the human eye?
WHY THE LEAF IS GREEN?
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ELECTROMAGNETIC SPECTRUM WAVES…in details I.
Radio waves:
•emitted by radio stations, during transmission or by TV stations etc. they are
also emitted by stars.
•range from few millimeters to large wavelength.
•used by antennas.
•used for data transmission via modulation, majorly used for communication.
Micro waves:
•emitted by the microwave oven (heating the food).
•initial use: in long range communication.
•used by astronomers to study the structures of galaxies.
•two types: super high frequency and extremely high frequency.
•used by Wi-fi.
Infrared rays:
•are emitted by everything that is warm and hot.
•have three types:
- Far infrared rays (15 - 1000 μm wavelength range)
- Mid infrared rays
- Near infrared rays (0.75-1.4 μm wavelength range)
•infrared spectrometers are generally used to study the vibrational spectra of
molecules
ELECTROMAGNETIC SPECTRUM WAVES…in details II.
Visible light :
•are emitted by everything from a bulb to particle striking other particles
•are detected by human eye
•wavelength lies between ~ 400 nm to 700 nm (from violet to red)
•are used in optical fiber communication medium
Ultraviolet :
•are emitted by sun
•harmful for human body, cause skin burn, can cause skin cancer
•can ionize atoms → mutagen
•are absorbed by ozone layer mostly
X-rays :
•are used by doctors
•can interact with matter
•are produced by the sudden stoppage of the high speed charged particle by
the use of metal target which absorbs these particles and the x-rays are emitted
by such particles.
•have two types: - hard ray
- soft X-ray
Gamma rays :
•are emitted by radioactive substances (produced by the radioactive decay of the radioactive atoms)
•are used in treatment of many diseases
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COULD YOUR PHONE HARM YOUR HEALTH?
Do mobile phones cause cancer?
•mobile phones emit and receive radio and microwave radiation
non-ionising radiation
•only heating effect (?)
•we don’t know
AND WHAT ABOUT BANANA?
Is it dangerous to eat banana because of its
radiation?
no (of course
)
PROBLEM SOLVING
A light wave is an electromagnetic wave that has both an electric and magnetic
component associated with it. Electromagnetic waves are often distinguished
from mechanical waves. The distinction is based on the fact that
electromagnetic waves ______.
a. can travel through materials and mechanical waves cannot
b. come in a range of frequencies and mechanical waves exist with only certain
frequencies
c. can travel through a region void of matter and mechanical waves cannot
d. electromagnetic waves cannot transport energy and mechanical waves can
transport energy
e. electromagnetic waves have an infinite speed and mechanical waves have a
finite speed
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PROBLEM SOLVING
Consider the electromagnetic spectrum as you answer these three
questions.
a. Which region of the electromagnetic spectrum has the highest frequency?
b. Which region of the electromagnetic spectrum has the longest wavelength?
c. Which region of the electromagnetic spectrum will travel with the fastest
speed?
PROBLEM SOLVING
Consider the visible light spectrum as you answer these two
questions.
a.
Which color of the visible light spectrum has the greatest frequency?
b.
Which color of the visible light spectrum has the greatest wavelength?
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Thank you!
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