Transcript Understanding Sound Waves,Ultrasound and the

Understanding Sound
Waves,Ultrasound and the
Electromagnetic Spectrum
Physics Revision Lesson 2
In this lesson you will revisit:
• Sound waves (particularly ultrasound).
• Seismic Waves
• The Electromagnetic Spectrum
Sound Waves
• Can be reflected and refracted.
• Echoes are due to reflected sound.
• The amplitude of a sound wave is a measure of
how much energy is being carried. Bigger
amplitude means louder sound.
• Frequency of a sound determines its pitch.
Frequency is measured in hertz. High frequency
leads to high pitch and vice versa.
Wave Traces
A high pitch sound.
A quiet sound.
A low pitch sound.
A louder sound.
Ultrasound
• This is sound with a higher frequency than
we can hear, i.e. above 20000 Hz.
• Uses include: industrial cleaning, breaking
down kidney stones, industrial quality
control, scanning of unborn babies and
SONAR.
Using Sound Waves : Ultrasound
Ultrasound has many uses, especially in medicine where it
is used to scan the foetus.
 A louder sound.
10 weeks
20 weeks
Why
doare
doctors
ultrasound
to scan the and
foetus
X rays
more use
energetic
and penetrating
areand
a lotnot
more
X
rays whichthey
givecould
a clearer
picture?
dangerous,
cause
damage to the growing baby.
Seismic Waves (Earthquake Waves)
During an earthquake the two types of wave that are
released from the epicentre are primary waves (p-waves)
and secondary waves (s-waves).
Primary or p-waves are the fastest. They are
longitudinal in nature and when they hit the surface they
make objects and buildings vibrate vertically. They can
travel through solids and liquids.
Secondary or s-waves are the slowest. They are
transverse in nature and when they hit the surface they
make objects and buildings vibrate horizontally. They can
only travel through solids.
Earth’s Structure
You will need to know how seismic waves can tell us
about the Earth’s structure.
Outer core
Crust
Mantle
Inner core
Electromagnetic Spectrum
Although all e-m waves travel at the same speed, their
wavelength [] and frequency [ƒ] can be different.
Waves that cook food.
Waves that cause
sun-tans.
The properties, dangers and uses of e-m waves depends
on the wavelength [].
Electromagnetic Spectrum
Wavelength () increases
Radio
Micro
InfraRed
Light
UltraViolet
X rays
Gamma
Gate
X of a phrase
Usually
Letshelp you
Inremember
Radiation
Can
you
think
that would
Low Most
frequency
this order?
High
frequency
Highfrequency
frequency
Low
Long wavelength
Short wavelength
High energy
Short wavelength
wavelength
Long
Low energy
Most penetrating
Highenergy
energy
Low
Least penetrating
Most penetrating
Least
penetrating
Electromagnetic Spectrum
Uses and dangers of EM radiation
Research the uses and dangers of the various radiations:
Radiation
Gamma
X-rays
Ultraviolet
Light
Infra red
Microwaves
Radio waves
Uses
Dangers
EM Radiation:
Gamma
Uses:
Kills harmful bacteria in
food, sterilising surgical
equipment, killing cancer
cells.
Dangers:
High doses can kill cells.
Lower doses can cause
cells to become cancerous.
EM Radiation:
X rays
Uses:
Shadow pictures of
luggage and inside the
human body.
Dangers:
High doses can kill cells.
Lower doses can cause
cells to become cancerous.
How do hospital workers
limit their exposure to
Gamma and X rays?
Hospital workers limit
exposure to Gamma and
X rays by standing behind
lead shields or by leaving
the room when the
radiations are being used.
X rays
How are X rays slides formed?
X rays can
penetrate soft tissue
but not b_____.
X
one
rays are a_______
bsorbed
more by some
materials than
others. P________
hotographic
f____
ilm is used to
detect X rays.
EM Radiation:
Ultraviolet
Uses:
Sun beds, fluorescent
lamps and security
marking.
Dangers:
High doses can kill cells.
Lower doses can cause
cells to become cancerous.
Which type of radiation is
the most dangerous?
The higher the frequency
of the radiation, the more
dangerous it is. So
gamma is more
dangerous than X rays or
ultraviolet.
Effects of EM radiation on living cells
Ultraviolet
Infra
red radiation
radiationiscan
used
pass
in toasters,
through grills
skin to
and
deeper
radiant
heaters.
tissues.
What
has
on your
skin?
What effect
effect do
do you
you think
think itthe
colour
of the
skin has on
the amount of radiation that passes through it?
The darker the skin, the more ultraviolet radiation is
absorbed, the less can reach into deeper soft tissues.
EM Radiation:
Light
Uses:
Seeing and endoscopes
Dangers:
Blindness
EM Radiation:
Infrared
Uses:
Remote controls (TV/VCR),
radiant heaters, grills, optical
fibre communication, night
vision.
Dangers:
Skin burns
Night vision
All objects above
absolute zero emit
infrared radiation. The
hotter an object is, the
more heat radiation it
emits. Some animals
and cameras can detect
infrared radiation and
are able to build up a
heat picture.
Which are the
hottest/coolest parts of
the image shown?
light is hot
dark is cold
EM Radiation:
Microwaves
Uses:
Satellite communication,
mobile phone networks,
cooking, RADAR.
Dangers:
Internal tissue heating.
Microwaves
How do microwaves cook foods?
Microwaves can be used in
c_____
ooking because many foods
ater molecules.
contain w____
Microwaves of the right
avelength are able to make
w________
the water molecules r_______.
esonate
This causes the food to get
h____.
otter
Radio waves
EM Radiation:
Radio waves
Uses:
Communication and
astronomy.
Dangers:
Radio waves
How do radio signals from the UK reach around the globe?
The longer
wavelength radio
waves from a
transmitter reflect
off the Earth’s
outer atmosphere
(ionosphere).
Getting hotter
If electromagnetic radiation is incident upon a
material what effects could it have?
An alternating current could be induced in the material,
with the same frequency as the incident radiation.
The temperature of the material could increase.
21º C
30º
50º
70º
What is the upper range of human hearing?
A. 20 Hz
B. 200 Hz
C. 2 000 Hz
D. 20 000 Hz
What causes all sounds?
A. Vibrations
B. Reflections
C. Refractions
D. Heat
Which of the following can sound not
travel through?
A. Liquid
B. Vacuum
C. Solid
D. Gas
A ship releases an echo sounding and 4
seconds later receives a signal from the
seabed, how deep is the sea?
(speed of sound in water is 1500 m/s)
A. 6000m
B. 375m
C. 750m
D. 3000m
Which of the following is not a use
of ultrasound?
A. Prenatal scanning
B. Quality control in industry
C. Cleaning delicate machinery
D. Cooking food
EM Questions
1)
Match up the following parts of the electromagnetic
spectrum with their uses :
Gamma rays
Allow us to see
Radio waves
Remote Controls
Ultra Violet
‘See’ broken bones
Visible
Carry TV signals
Microwaves
RADAR
X rays
Sterilise equipment
Infra Red
Causes sun-tans
EM Questions
2) Which radiations are missing from below?
Gamma
A
Ultraviolet
Light
Infrared
A. ___________
X rays
B. ___________
Microwaves
B
Radio waves