An Introduction to Waves for Students (with its own activity sheet!)

waves are disturbances that carry energy

from one place to another

there are many different types of waves

for example slinky waves

sound waves

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water waves

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that's not me by the way

that's me

finally

and the seismic waves the waves

generated

by earthquakes

all of these waves are called mechanical

waves

because they need what's called a medium

to travel through

in a slinky wave for example the slinky

is the medium

the movement of one coil makes the next

one move

which makes the next one move and so on

this basic process occurs in all

mechanical waves

when each coil moves perpendicular to

the direction of the wave

the wave is called a transverse wave

each loop is moving only up and down as

the wave

moves from left to right

you can see that the blue tape on one of

the coils does more or less the same

thing

the waves move sideways but each

particle moves only up and down

one of microsoft's powerpoint animations

is called

wave and it creates a transverse wave

by moving each letter up and down

when each coil moves side to side in the

same direction

that the wave is traveling in the wave

is called a longitudinal wave

each loop is moving first to the right

and then to the left

as the wave moves from left to right

sound waves are longitudinal waves

electromagnetic waves are different from

all other types of waves

in that they don't need a medium to

travel through

the light coming from the sun for

example can get to us here on earth

even though the space between the earth

and the sun

is a vacuum light doesn't need a medium

because it's a self-contained wave of

electrical

and magnetic energy

can represent a wave with a simple

diagram

we'll use a transverse wave because it's

so much easier to picture

most waves in nature have a positive and

a negative component

the top of the wave is called a crest

while the bottom of the wave

is called a trough the so-called

wavelength of a wave is the distance

from one crest to the next

or from one trough to the next this

distance

is also the wavelength wavelength is

usually measured in meters

the greek letter lambda which is the

greek letter l

is used as the symbol for wavelength so

if the wavelength was 2 meters i would

label this diagram

by writing lambda equals 2 meters

but i would read this as wavelength

equals 2 meters

a wave's amplitude is the height of the

crest of the wave

or if you like the depth of the trough

this wave has an amplitude of about 40

centimeters

when two waves meet they pass straight

through each other

here a larger amplitude wave pulse

moving towards the right

meets a smaller amplitude wave pulse

moving towards the left

after they pass through each other the

larger wave pulse is still moving

towards the right

and the smaller wave pulse continues

moving towards the left

if waves didn't pass through each other

then for example

all the light reflecting off me towards

the camera would crash into all the

light reflecting off the camera

towards me the light waves would bounce

off each other

and scatter in every direction all we

would see

is a blur of light at the point where

the waves meet

the amplitudes of the waves add up this

is called

superposition this amplitude

plus this amplitude equals this

amplitude

when the two waves superimpose

if the wave pulses are on the opposite

side of the slinky

the waves superimpose to temporarily

reduce in overall amplitude

before moving on

frequency given the symbol f

is the number of complete wavelengths

that pass a given point

per second it's measured in hertz

the frequency of the top wave is one

hertz

one complete wavelength is being

produced per second

while the frequency of the bottom wave

is two hertz

here i've attached this signal generator

to this speaker

i've set the output to 1 hertz so the

speaker is vibrating

once per second i can increase the

frequency to 2 hertz

that is 2 vibrations per second

and then to three hertz

four hertz and so on

humans can hear sounds only if they're

above about

20 hertz this is 60 hertz

90 hertz

400 hertz 800 hertz

and about 9 000 hertz

humans can hear only up to about 20 000

hertz

my ears are starting to hurts

thanks for watching this short excerpt

from shedding light on electromagnetic

waves

the sixth program in the shedding light

on light series of programs

aimed at high school students studying

the topic of light

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the program begins with an introduction

to electromagnetic waves

how electricity and magnetism are

related

how james clark maxwell came up with the

idea of an electromagnetic wave

how heinrich hertz actually proved their

existence

and how gulielmo marconi started using

radio waves

in long range communications

we then look at waves in general we look

at transverse waves and longitudinal

waves

wavelength frequency and wave speed

the rest of the video looks specifically

at electromagnetic waves

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radio waves and microwaves infrared

light

including thermal imaging and night

vision

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visible light including lasers and color

ultraviolet light and how it can cause

damage to unprotected

skin cells x-rays including radiography

and radiotherapy and finally

gamma rays and how they are used in

industry

visit our website to get details about

how you can watch the whole program

and to download the worksheet in fact

worksheets from every shedding light

program can be downloaded from the

website

and there's a whole bunch of practical

activities that you can download as well

thanks again for watching

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