# Wave & Electromagnetic

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16 Νοε 2013 (πριν από 4 χρόνια και 4 μήνες)

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Wave & Electromagnetic
Spectrum Notes

November 17, 2013

I.) Properties of Waves

A)
Wave
: A periodic disturbance in a
solid, liquid or gas as
energy

is
transmitted through a
medium
(
Waves carry energy b/c they do
“work”)

*Waves create “wave fronts” (circles)
that have the same amount of total
energy but as the circles get larger the
energy spreads out over a larger area.

1)
Mechanical Waves
: waves that
require a medium

through which to
travel

a)
Medium
: physical environment in

which phenomena occur

1) Example: water, air, Earth

b)
Almost all waves are mechanical

waves,
except EM waves

2)
Electromagnetic Waves
: waves
that consist of oscillating electric
outward at the speed of light (3.0
x 10
8

m/s) (
Holy Gazoli! That’s
fast!)

a) Example: visible light,
microwaves, etc.

b)
DO NOT

require a medium

Fun Wave Vocabulary Ha! Ha!

A)
Crest
: section of the wave that rises
above the equilibrium position

B)
Trough
: section which lies below the
equilibrium position

C)
Wavelength
: distance between one point
on the wave and the nearest point where
the wave repeats itself

1) This can be measured from
crest
-
to
-
crest, trough
-
to
-
trough
, or from the start
of a wave to the start of the next one.

2) Symbol for wavelength is λ

D)
Amplitude
: maximum displacement from
the undisturbed position of the medium to
the top of a crest.

E)
Period
(T): time required for one wave to
complete one full cycle of its motion

i.e.
The period measures how long it
takes for a wave to pass by

1)
Example: From its highest point to
its lowest and back again

2) Measured in
seconds

(s)

F)
Frequency
: the number of complete
waves that pass a point in a given time. It
has the symbol
f.

1) SI Units:
Hertz

(Hz)

2) Hertz units measure the number of
vibrations per second

ex. 1 vibration per second is 1 Hz, 2

vibrations per second is 2 Hz

3) Period is related to frequency in that the
frequency is the inverse of the period

Frequency = 1 / period

f = 1 / T

G)
Wave speed

1) The frequency and wavelength are
related to one another and to the speed of
the wave by the following formula, where
“v” is equal to the speed:

Speed = Wavelength x Frequency

v =

f

II.) Traveling Through Mediums

A)
Mechanical waves
require a medium

in order to
travel through

1) Waves are classified by the direction that they
travel through the medium

a)
Transverse Wave
:

the particles in the

medium move

perpendicular
to the

direction wave is traveling

1) Ex: Light waves

b)
Longitudinal Wave
: the particles in the
medium move
parallel

to the direction the
wave is traveling

1) Ex: Sound waves

C)
Surface Wave
-

occur at the boundary
of 2 different mediums (ex. Water and air)

Particles in a surface wave move both
perpendicular & parallel to the direction
the wave travels

The up/down motion combine w/ the side
to side motions to produce a circular
motion overall

Ex. Ocean waves

2) Speed and direction of these mechanical waves
are affected by the medium they encounter

a) Example: Sound waves travel very fast
through air, but they travel 3 to 4 times faster
under water

1) why so many animals use sound

waves to communicate (dolphins)

b) They travel even faster in a solid, producing
speeds 15 to 20 times faster in rock or metal.

Speed of sound waves in types of mediums

(slowest to fastest)

Gas

Liquid
→ Solid

III.)
Doppler Effect
: an observed change in the
frequency of a wave when the
source or observer

is
moving

A)
Pitch

of a sound (how high or low it is) is
determined by the frequency

at which the
sound waves strike the eardrum

1) When an
object

that is emitting sound waves
(i.e. ambulance) is
at rest
, the
sound waves

and anyone who is
standing near the object will hear the same pitch

2)
When an object that is emitting
sound waves

(i.e. ambulance) is
moving

however, the waves
are closer together in the direction of the motion.
So if
one person is standing in the same
direction as the motion
, the
pitch will seem
higher

than if a person was standing in the
opposite direction

IV) Wave Interactions

A)
Reflection
: the bouncing back of a ray of light,
sound, or heat when the ray hits a surface that
it does not go through

B)
Refraction
: the bending of waves at an
angle

when they pass from one medium into another

1) Ex: Spoon in glass of water appears to be
broken because the light waves are bending at
a different angle when they enter the water
versus the air

C)
Diffraction
: The bending of a wave when
the wave finds an obstacle or an edge,
such as an opening

1) Waves will
bend

around an object or
opening

a) Example: hear sounds clearly from

classroom only through open door

because waves spread out into the

space beyond the door

D)
Interference

1)
Constructive
Interference
: when two
waves interact and the
resultant wave has a larger
amplitude (Part A)

2)
Destructive Interference
:
when two waves interact and
the resultant wave has a
smaller amplitude (Part B)

*
HOW LOUD A SOUND IS
DEPENDS UPON THE
AMPLITUDE

OF THE
WAVES THAT INTERACT
!!

Standing wave
-

can form when a wave is
reflected at the boundary of a medium.

Interference occurs b/w the original wave
& the reflected wave

Causes wave to vibrate in a stationary
pattern (resembles loops)

Looks like wave is standing still but it
reality waves are traveling in both
directions

Standing wave components

Nodes
-

point that has
no vibration

&
separates the loops of a standing wave (lie
where the crest of original wave meets the
trough of reflected wave

Antinodes
-

point of
maximum vibration
;
form where the crests of the original wave
line up w/ the crests of reflected waves

Electromagnetic Spectrum Notes

I.) Electromagnetic Waves

A) What are EM Waves?

1) How are they produced?

a)
Electric

and
magnetic

fields are

constantly
changing

b) EM waves are produced when

electric

charges
vibrate

or
accelerate

2) How they travel

a) Since electric and magnetic fields are

constantly changing, they
regenerate

each

other

b) EM waves can travel through a
vacuum

(empty space) as well as through
matter

B) Speed of EM waves

1) Michelson (1852
-
1931) setup an
experiment to try and find how fast light
travels

2) Speed of light in a vacuum, c=
3.00x10
8
m/s

II.) Electromagnetic Spectrum

A) The Waves of the Spectrum

1) EM spectrum: all of the frequencies or

2) The EM spectrum includes

waves,
micro
waves
infrared

rays,
visible

light,
UV

rays,
X
-
rays
, and
gamma

rays.

-
Longest

wavelength

-
Lowest

Frequency

1) Radio waves are used in

&
TV

technologies, as well as in
.

1) Amplitude modulation (AM)

2) Frequency modulation (FM)

1) Send out
short

waves that
bounce

off objects &

return

C) Microwaves

-
Shorter

-
Higher

frequency than
, but
lower

than
infrared

1) Only penetrate food at the surface

D) Infrared Waves

-
Shorter

wavelength than
microwaves

-
Higher

frequency than
microwaves
, but
lower

than
red

light

1) Infrared rays are used as a source of
heat

& to discover areas of
heat

difference

2) You can’t see infrared radiation, but
warmth

E) Visible Light

-
Each
wavelength

corresponds to a
specific

frequency

**
C
o
l
o
r

determined by frequency

1) People use visible light to
see
, help
keep them
safe
, and to
communicate

with
one another.

F) UV Rays

-
Shorter

wavelength and
higher

frequency
than violet light

1) UV rays have applications in health and
medicine, and in agriculture.

a) Helps
skin

produce Vit.
D
,

can cause
sunburn
,
cancer
,

and used to kill
microorganisms

G) X
-
Rays

-
Shorter

wavelength and
higher

frequency than UV
rays

1) X
-
rays are used in
medicine, industry, and
transportation to make
pictures of the inside of
solid objects.

a) X
-
rays are absorbed

by
solid

objects (teeth,

bones) & so
solid

objects appear
white

H) Gamma Rays

-
Shortest

wavelength

-
Highest

frequency

1) Gamma rays are used in the
medical

field to kill
cancer

cells and to make
pictures

of the
brain

& in industrial situations as an
inspection

tool.