Waves FULL

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Waves
LI:
1 - Define a wave.
2 - Name the two kinds of wave.
3 - Describe waves by their properties
4 - Learn to use the wave equation and state
the meaning of all its parameters.
Starter
Draw the diagram.
Which way does the cork move?
Wave Motion
Cork bobs
ups and down
Water
Looking at Waves
What is a wave?
A wave is simply a movement of energy…
11/01/2019
Transverse waves are
when the displacement is
at right angles to the
direction of the wave…
Example Light
Particle
Displacement
Transverse vs. longitudinal waves
Wave Direction
Particle Displacement
Longitudinal waves are
when the displacement is
parallel to the direction of
the wave…
Example Sound
Wave Direction
11/01/2019
Learning Objectives
1. Be able to describe a wave in
terms of wavelength, frequency
and amplitude.
2. Be able to use the wave equation
in calculations:
V=f
Some definitions…
1) Amplitude – this is
“how high” the wave is:
2) Wavelength () – this is the
distance between two identicle
points on the wave and is
measured in metres:
3) Frequency – this is how many waves pass by
every second and is measured in Hertz (Hz)
• Wavelength is the distance from one peak to the
next
• It is also the distance between one point on a
wave to the next identical point on the next
wave.
• Frequency is the number of waves produced
each second.
• It is also the number of waves that pass a point
each second.
• Amplitude is the maximum displacement of a
wave from its mean (middle ) position. For sound
waves this represents the volume.
Using an oscilloscope
1) Quiet sound, low frequency:
2) Quiet sound, high frequency:
3) Loud sound, low frequency:
4) Loud sound, high frequency:
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Wave Speed – Complete the Table
Wave
Water
wave
Mexican
wave
Musical
note
Rope
Ultrasound
[Hz]
 [m]
2
1.5
MW1
?
256
3
35,000
V [m/s]
10
339
0.8
339
Exam Questions
1
The wavelength is the _______________ from
one wave peak to the next wave peak along the
waves.
2
The frequency of electromagnetic waves of a
certain wavelength is the number of complete
waves passing a point each _______________.
3 wave speed = ____________ _____________
(metre/second, m/s) (hertz, Hz)
(metre, m)
Exam Questions
2 The number of waves passing a point
each second is the …
A amplitude
C speed
B
D
frequency
wavelength
(1)
Starter – What are the 3 characteristics
of a wave and what are they?
What you need to know for the exam
• .
• .
• .
• .
• .
• .
Wave Animation
Wave definitions…
11/01/2019
1) Amplitude – this is
“how high” the wave
is:
2) Wavelength () – this is the
distance between two
corresponding points on the
wave and is measured in metres:
3) Frequency – this is how many waves pass by
every second and is measured in Hertz (Hz)
4) Speed – this is how fast the wave travels and is
measured in metres per second (m/s)
The Wave Equation
The wave equation relates the speed of the
wave to its frequency and wavelength:
Wave speed (v) = frequency (f) x wavelength ()
in m/s
=V
in Hz
and
in m
=V
Distance, Speed
and Time for waves
Speed = distance (in metres)
time (in seconds)
1) A water wave travels 200 metres in 40 seconds. What is its speed?
2) Another wave covers 2km in 1,000 seconds. What is its speed?
3) Sound travels at around 330m/s. How long does it take to travel one
mile (roughly 1,600m)?
4) Light travels at a speed of 300,000,000m/s. How long would it take to
travel around the world if the diameter at the equator is around
40,000km?
Some
definitions…
Transverse waves are
when the displacement
is at right angles to the
direction of the wave…
Longitudinal waves
are when the
displacement is
parallel to the
direction of the wave…
6
No. of waves: 14
3
0
5
20
15
9
11
19
16
1
7
12
17
2
13
8
18
4
Wavelength:
20 cm
05
03
10
08
04
06
01
02
07
00
0:00. 09
Each wave is 20 cm long and 2
So
the
formula
for
This
is
the
speed
20
No.
of
waves
per
waves:
waves pass the float every
second
so how
many
cm of wave
speed
of
a
wave
is:
of
the
wave.
second
is
known
as
pass the float per second?
10
s
Time:
frequency,
so:
Speed
x wavelength
2 lots =
offrequency
20 cm is 40
cm per s
2
Waves
per
(2
Hz x 20
cmsecond:
= 40
cm/s)
Frequency
=
2
Hz
V = f x 
No. of waves: 1
3
5
2
4
Wavelength: 3 m
05
03
10
08
04
06
01
02
07
00
0:00. 09
So
formula
Thisthe
is waves
the
speed
5for
No.
of
per
waves:
speed
wave as
is:
of the of
wave.
second
is aknown
10
s
Time:
frequency,
so:
Speed
x wavelength
½ of 3 =mfrequency
is 1.5 m per
second
Waves
(0.5
Hz xper
3 msecond:
= 1.5
m/s)0.5
Frequency
=
0.5
Hz
V = f x 
Each wave is 3 m long and ½ a
wave passes the boat in 1 s so
how many metres of wave pass
the boat per second?
Water waves collide with a wave generator
with a frequency of 2 Hz. Their
wavelength is 4 m, so their speed is …
2 m/s
8 m/s
0.5 m/s

A loudspeaker produces sound waves of
frequency 680 Hz and wavelength of 0.5 m.
Their speed is …
340 m/s
1320 m/s
33 m/s

A ship’s klaxon produces sound waves of
frequency 170 Hz. Sound waves travel at
340 m/s, so their wavelength is …
2m
0.5 m
57800 m

Bats produce ultrasound waves with a
wavelength of 0.01 m. Their speed is
330 m/s. The frequency of the waves is …
3.3 Hz
33000 Hz
0.0003 Hz

The wavelength of Radio Whitcliffe is
100 m. The frequency of the waves is
3000 kHz., so their speed is …
3 m/s
300 000 m/s
300 000 000 m/s

The wavelength of yellow light is 6 x 10-7 m
and the speed of electromagnetic waves is
3 x 108 m/s. Their frequency is …
2 x 1015 m/s
18 x 101 m
5 x 1014 Hz

Ripples cross a pond with a speed of 80 cm/s.
They reach the edge at a frequency of 20 Hz.
Their wavelength is …
4 m/s
80 cm/s
0.04 m/s

This lesson you are going to
learn:
• What qualities make a good and bad
reflector.
• That the angle in which light strikes a
mirror is equal to the angle in which
it is reflected.
Good v Bad Reflectors
• Smooth, shiny
surfaces have a clear
reflection:
Rough, dull surfaces have a
diffuse reflection.
Diffuse reflection is when
light is SCATTERED IN
DIFFERENT DIRECTIONS
Good
reflectors
Bad reflectors
Draw this table into your book. Put the following
objects under the correct heading:
Mirror, foil, tree bark, tarmac, shiny shoes,
cardboard
Good reflectors
Bad reflectors
mirror
foil
shiny shoes
cardboard
tarmac
tree bark
Copy and complete:
Some materials are better at _______ light than
others. Shiny, smooth surfaces are ______ at
reflecting light and rough, matt surfaces are ____
at reflecting light. The light that is not reflected
is _________ or _________by the object.
good
reflecting
scattered
absorbed
bad
Mirrors
A mirror is a good reflector of light.
Mirrors reflect light
This lesson you are going to
learn:
• What qualities make a good and bad
reflector.
• That the angle in which light
strikes a mirror is equal to the
angle in which it is reflected.
Law of Reflection
Write these steps in the correct order.
• Using a ray-box send a narrow beam of
light along the line marked 20 .
• Measure the angle of reflection, put
result in a table.
• Repeat using different angles.
• Put the mirror with its back along the
line marked ‘mirror’.
Correct order:
1. Put the mirror with its back along
the line marked ‘mirror’.
2. Using a ray-box send a narrow
beam of light along the line
marked 20 .
3. Measure the angle of reflection,
put result in a table.
4. Repeat using different angles.
Angle of incidence
Angle of reflection
Results
Angle of Angle of
incidence reflection
20°
30°
40°
50°
60°
70 °
80°
Conclusion
The law of reflection:
The angle of incidence
equal ___
to the
is ______
angle of reflection.
Choose the correct
words:
•Greater than
•Less than
•Equal to
Draw a graph of your results:
Angle of
reflection
Angle of incidence
Angle of reflection
Graph to show the angle of reflection with
changing angles of incidence.
90
80
70
60
50
40
30
20
10
0
20
30
40
50
60
Angle of incidence
70
80
Mirrors: Draw a diagram to show what you have learnt
about the reflection of light in a plane mirror.
Include: Normal line, angle of incidence, angle of
reflection, the mirror, light source, the eye.
Normal line
Angle of
incidence
Angle of
reflection
Incident ray
Reflected ray
angle of incidence = angle of reflection
This lesson you are going to learn:
• What qualities make a good and bad
reflector.
• That the angle in which light strikes a
mirror is equal to the angle at which
it is reflected.
The law of reflection
The angle between the incidence ray and the
normal is the same as the angle between the
reflected ray and the normal.
Summary:
Complete the following sentences. Include one of the
following words or phrases in each answer.
and because but
so to
1
2
3
4
5
6
7
8
however
such as therefore
Light cannot travel through opaque objects …
Light travels in straight lines …
Light travels much faster than sound …
Most objects reflect light …
The surface of a mirror is very smooth …
The normal is a line at 90° to the mirror …
Our eyes have a hole called the pupil …
Cameras and eyes are different in some ways …
which
Refraction
LI: What happens to light
when it passes through
different materials?
1.Draw around your glass block
2.Shine your ray of light in at an angle
3.Draw the path of the ray of light on
either side of the block
1.Connect up your rays
What is refraction?
The bending of light as it
travels though different
materials
Why does refraction happen?
Refraction in a rectangular
block
Copy and complete
When light passes through glass it
………………. Direction. The rays
are ……………….. This is called
…………………….. Refraction
happens as the light ray changes
………………………….. As it
travels through different materials.
If light slows down it bends
towards the ……………………. As
light speeds up it
…………………… away from the
Many visual effects are caused by
refraction.
This ruler appears bent
because the light from one end
of the ruler has been
refracted, but light from the
other end has travelled in a
straight line.
Would the ruler appear
more or less bent if the
water was replaced with
glass?
Visible light and Refraction
11/01/2019
L.O.
To apply knowledge of the EM
spectrum and refraction to the
process of dispersion
Be able to explain dispersion
Success Criteria:
 To recap EM
spectrum and
refraction
 To explain
what happens
to white light
when travelling
through a
prism

To collect
detailed
information

To write
extended
scientific
explanations
To recap EM spectrum and
refraction
5 minutes
Green Pens… Self
Assess…Improve
 Which part has the highest
frequency?
 Which part has the lowest
frequency?
 Which parts surround visible light?
 which parts have the 3 shortest
wavelengths?
 which parts have the 3 longest
wavelengths?
 What is happening in the
diagram?
 Why does this happen?
EXTEND: WHAT WILL
HAPPEN HERE?
Think… what
part of the EM
spectrum is
shown on this
diagram
What will
happen to it?
Why?
The BIG question
Explain what happens to white
light when it shines through a
prism. Use a common example
to describe where this can
occur.
To Answer this you will
Collect information (key words,
meanings, diagrams)
Write a draft
Peer assess - 2 stars a wish and a
steal
Redraft
To Answer this you will
Collect information (key words,
meanings, diagrams)
Describe what happens to white
light when travelling through a
prism
Pick up your prism… what can you
see… be specific
Does your partner see the same?
Refraction in a prism is called
Dispersion
White light
(visible light)
Because white light is split up
(dispersed) into its separate
colours
SPECTR
UM
Describing – saying what
happens
BUT we need to…
EXPLAIN 

rainbow are refracted
different amounts
depending on their
Which part of visible light is
wavelengths
refracted the most?/least?
 Use clues in your EM wave
diagram below as to which
colour light has the
longest/shortest wavelength
 What is dispersion
 What does it depend on?
 Which colour is refracted
most why?
 Which colour is refracted
least and why?
How are rainbows formed?
Reviewing information:
Do you need to ask a partner for
clarification?
Is there any thing you did not
2 minutes
get?
Ensure you have all the
information you need
Can you say what dispersion
is? How it happens? What is
formed? Why it happens?
10 minutes
Preparation Stage 4: Redraft and
teacher assessment
How do we see colour?
11/01/2019
L.O.
To EXPLAIN how we see coloured
objects.
To apply to assessment questions
How do we see?
The Electromagnetic Spectrum
Gamma rays have a very short wavelength and have the
highest frequency. They are very penetrating (can get deep
into an object). They are produced by radioactive substances
and are dangerous to humans unless used very carefully.
Gamma-rays can be used to sterilise food. You seal the
packet, then blast the packet with gamma rays. This will kill
any microbes inside. New microbes cannot get into the sealed
pack. Once the burst of radiation is turned off, the radiation
is immediately gone, this ensures food stays fresher for
longer. Gamma rays can be used to check that two pieces of
metal have been welded together properly (notice the cracks
near the joint, bottom right)
Gamma radiation can also be used to sterilise medical
equipment after operations so that it can be used again. (It
kills microbes but doesn’t get hot, so won’t damage plastic
objects)
A carefully controlled beam of gamma rays is used to kill
cancer cells. This is radiotherapy. In the TV programme ‘The
incredible hulk’, exposure to gamma rays was the reason that
Dr Bruce Banner turned into the angry monster called the
hulk.
X-rays are very like gamma rays, but are produced by an Xray tube. They are the second highest frequency waves and
have the second shortest wavelength. Doctors and dentists
use X-rays to check bones and teeth.
As with gamma rays, X-ray photos are used by engineers to
check welds and metal joints
In factories X-rays can be used to check that food does not
have hard things like metal or stones in it.
X-rays are harmful if you get many doses or if you have a
large dose in one go because they can lead to cells becoming
cancerous.
Ultra-violet rays can also be dangerous to us. Hot objects
like the Sun produce ultra violet rays, and so do the electric
arcs used in electric welding.
Ultra violet has the 3rd highest frequency.
Large amounts of ultra violet are bad for our eyes and can
cause cataracts or skin cancer!
Ultraviolet rays can also cause suntan. The darker your skin,
the more UV it absorbs, and so less UV passes through to the
living cells underneath, meaning less damage.
Small amounts of ultra violet rays are good for us, producing
vitamin D in our skin. Vitamin D is needed for healthy strong
bones.
A chemical pigment in skin
Lack of
vitamin D
can cause
rickets
These ladies are
from India.
People whose
ancestors lived in
sunnier parts of the
world are more likely to
have darker skin
This lady is
from
Sweden.
The melanin in our skin absorbs UV rays, stopping it from
penetrating into the skin tissues, so it can’t damage our
cells.
UV Light
Melanin protects the
skin from UV light
Luckily for us, most of the Sun’s UV is absorbed high in the
atmosphere by the Ozone layer.
Some chemicals fluoresce (glow up) when they absorb UV rays,
and convert the energy into light rays so that your shirts look
brighter in sunlight.
Some insects can see UV light and it helps them to find
flowers
Effects of exposure to UV radiation from the
sun
Gives
a tan
Cancer
Can alter
your mood,
reducing the
risk of
depression
Helps vitamin
D production
in the body
Enjoyable
Sunburn
Causes early
aging
(wrinkles)
Relaxing
Visible light is the only part of the full spectrum that we can
see, it has the middle frequency and is not damaging.
Our eyes are more sensitive to some wavelengths than to
others. We see green and yellow colours more easily than reds
and violets.
Visible light is used for our eyes to see. It is also used for
taking photographs.
Visible Light was used in times gone by as a means of
communication; people would flash lights in Morse code to get
messages from one place to another quickly.
Visible Light is also used for safety – we have lights on cars
for driving in the dark or in foggy conditions. Light reflects of
cats-eyes on the motorway to let drivers know what lane they
are in.
Visible Light is also used in lighthouses to warn ships that they
are near underwater rocks that could damage their ship or
cause it to run aground.
Special photographs taken with infra red rays are called
thermographs. This means that people with illnesses that give
you a higher body temperature, such as swine flu, can be
detected at airports with infra red detectors. These viewers
can also be used by doctors to help detect circulation
problems (where the skin is cooler, so the thermograph is
bluer) and arthritis and cancer (where the skin is warmer)
Infra red rays are given out by
warm objects. This means that fire
fighters can use infra red viewers to
search for unconscious people in
smoke filled buildings, and to search
for survivors trapped alive by
earthquakes.
Infra red detectors are also used to find out which buildings
are not very well insulated. We know this because those
buildings will glow white and red on detectors, but well
insulated buildings have dark colours.
Astronomers take infra red photos to get data about the
temperature of planets and stars. Burglar alarms are designed
to detect the infra red rays from an intruder. Night vision
goggles also help the army to see the enemy in the dark.
Remote controls use infra red rays.
Microwaves are shorter than radio waves. They are used in
microwave ovens. Microwave ovens are able to cook food
because the frequency the wave is at is absorbed by water
molecules in the food. It vibrates the molecules, generating
heat, which is then transferred to the food.
Microwaves are reflected off metals, so microwave ovens have
metal mesh screens on the doors to stop the waves getting out
and burning you.
Microwaves are also used for communication with satellites
because they can get through the atmosphere.
Today, microwaves are also used for global positioning systems
on ‘sat nav’s’ and they are used to make mobile phone
communication possible.
Radio waves have a very long wavelength. There are many
types of radio wave.
UHF waves (ultra high frequency) are used to transmit TV
programmes to your home and to your radio (who’d have
thought).
Phone and WiFi signals also use radio waves.
VHF (very high frequency waves) are used to transmit local
radio programmes, and local police and ambulance messages.
Medium wave and long wave radio are used to transmit over
long distances. Because they have long wavelengths, they can
diffract (bend) around the curve of the Earth and around hills
that might be in the way.
The Image in a Plane Mirror
Watch the animation then draw a diagram to show
how we see an image in a plane (flat) mirror.
image
The ______is
the same size as the object and seems
to be behind
______ the mirror. Left and right are
reversed
___________.
Seismic Waves
Learning objective:
What are P waves and S waves
Seismic waves
Earthquakes travel as waves through the Earth – we call them
SEISMIC WAVES. There are two types:
P waves:
1) They are longitudinal so they cause the ground
to move up and down
2) They can pass through solids and liquids
3) They go faster through more dense material
S waves:
1) They are transverse so they cause the ground
to move from right to left
2) They ONLY pass through solids
3) They are slower than P waves
4)11/01/2019
They go faster through more dense material
11/01/2019
11/01/2019
Seismic waves
Earthquakes travel as waves through the Earth – we call them
SEISMIC WAVES. There are two types:
P waves:
1) They are _______ so they cause the ground to
move _______ and _______
2) They can pass through _______ and _______
3) They go faster through more dense material
S waves:
1) They are _______ so they cause the ground to
move from _______ to _______
2) They ONLY pass through _______
3) They are _______ than P waves
4)11/01/2019
They go faster through more dense material
Words: left, right,
transverse, longitudinal,
up, down, faster, slower,
solids, liquids
Seismic waves
11/01/2019
These P waves are being
reflected at the crust
These P waves travel through
the Earth and are refracted
when they pass through a
medium
The paths of these waves are all
curved because density is
11/01/2019
gradually changing
These S waves cannot
travel through the
outer core as they only
go through solids – this
tells us that the outer
core is liquid
Locating Earthquakes
11/01/2019
By measuring the time
it takes the wave to
travel to these
locations the location
of the earthquake can
be found.
11/01/2019
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