Transcript Mod_6_revision[1] - All Hallows Catholic High School

Waves, and space
EDEXCEL Module 6
Some pictures from
www.gcse.com
M Hancock, Chapter School
waves
space
Waves
• A Transverse wave is where the vibrations are at
right angles to the direction the wave is travelling in
Waves
Transverse waves include:
ultra-violet waves
Waves
Transverse waves include:
light waves
Waves
Transverse waves include:
micro waves
Waves
Transverse waves include:
radio waves
Waves
Transverse waves include:
X-rays
Waves
Transverse waves include:
gamma rays
Waves
• Longitudinal waves are when the
vibrations are in the same direction the
wave is travelling in:
Waves
• Sound waves are longitudinal!
Waves
• Earthquake
P-waves
waves are
longitudinal
Waves
• Ultrasound waves are longitudinal!
Waves
The length of one complete cycle of a wave is the
wavelength. This is measured in metres.
Waves
The amplitude of a wave is how big the vibrations
are. It is how far the vibrations move from their
normal position. For sound waves, amplitude
effects volume, for light waves amplitude effects
brightness or intensity.
Waves
The frequency of a wave is how many vibrations
there are per second. If the wavelength is small
then you will have lots of waves per second so
the frequency will be high.
Frequency is measured in Hertz (Hz).
High frequency sound waves have high pitch,
high freqeuncy electromagnetic waves have
more energy and are more dangerous.
Exam question:
Exam question:
The electromagnetic spectrum
The electromagnetic spectrum is a group of
waves that:
• All travel through space at the speed of light
• Are all transverse
• Are all made up of electric and magnetic force
fields
• Have more energy if the frequency is high
(small wavelength)
• Have less energy if the frequency is low (long
wavelength)
The electromagnetic spectrum
Exam question:
Some infra-red and ultraviolet waves travel
from the Sun to Earth. In space, they all
have the same:
A
Speed
B
Frequency
C
Wavelength
D
Colour
Exam question:
Some infra-red and ultraviolet waves travel
from the Sun to Earth. In space, they all
have the same:
A
Speed
B
Frequency
C
Wavelength
D
Colour
Exam question:
Compared to X-rays, radio waves have:
A
A longer wavelength and higher speed
B
The same speed and a lower frequency
C
The same wavelength and a higher speed
D
The same speed and a higher frequency
Exam question:
Compared to X-rays, radio waves have:
A
A longer wavelength and higher speed
B
The same speed and a lower frequency
C
The same wavelength and a higher speed
D
The same speed and a higher frequency
The electromagnetic spectrum
Gamma rays are used for sterilising food, sterilising
medical equipment, and treating some cancers
The electromagnetic spectrum
X-rays are used for seeing the internal structure of
things, including the human body
The electromagnetic spectrum
Ultraviolet light is used for sunbeds, security marking,
fluorescent lamps and detecting forged bank notes
The electromagnetic spectrum
Visible light is used for vision (!) and photography
The electromagnetic spectrum
Infra-red is used for grills, night vision, remote controls,
security systems and treatment of muscular problems
The electromagnetic spectrum
Microwaves are used for cooking and communications
including satellite transmissions
The electromagnetic spectrum
Radio waves are used for broadcasting and
communications including satellite transmissions
Exam question:
Exam question:
Some practice questions
Some practice questions
Too much radiation
An overdose of microwaves can lead to internal heating
of body tissue
Too much radiation
An overdose of infra-red can lead to skin burns
Too much radiation
An overdose of ultraviolet can lead to damage to surface
cells (including skin cancer) and eyes
More on ultrasound
Ultrasound is high frequency sound waves – over
20,000Hz. Because it is a sound wave it is
longitudinal.
Ultrasound is used to scan for babies as sound
waves are not harmful to the babies like X-rays
would be. The echo from the ultrasound waves
is used to make a picture of the baby.
More on ultrasound
Ultrasound is also used for sonar – detecting what is
under a boat (ie: fish or rocks!).
More on ultrasound
You can’t hear
ultrasound because
the human ear can
only hear frequencies
of up to 20,000Hz
(20kHz). Ultrasound is
above 20kHz.
Some practice questions
Some practice questions
Refraction
Refraction occurs because
light travels slower
through glass or water
than it does through the
air.
When entering a more
dense medium, light
refracts towards the
normal. When leaving it
o
The
normal
is
a
line
at
90
refracts away from the
to the surface of the glass
normal.
or water where the light
hits it.
Another question:
Another question:
Another question:
Which of the following always changes when light is refracted:
A
The direction
B
The speed
C
The frequency
D
The colour
Another question:
Which of the following always changes when light is refracted:
A
The direction
B
The speed
C
The frequency
D
The colour
Refraction
When light passes through a prism, the
angles of the prism mean that the light gets
refracted the same way twice. Different
colours get refracted different amounts so
the white light is split up into a spectrum of
colours.
Optical fibres
Visible and infra-red light
can be passed down an
optical fibre, it bounces
along as it is reflected by
the edges of the fibres.
Very little energy is lost as
all the light is reflected.
The fibres are flexible and
can go round corners.
The beam of light can
carry information.
Some practice questions
Light changes speed when it goes from air
to glass.
This is called:
A Reflection
B Refraction
C Deflection
D Diffraction
Some practice questions
Light changes speed when it goes from air
to glass.
This is called:
A
B
C
D
Reflection
Refraction
Deflection
Diffraction
Some practice questions
Ultrasound:
A
Is a transverse wave
B
Can pass through a vacuum
C
Has a frequency greater than 20,000Hz
D
Is an electromagnetic wave of high frequency
Some practice questions
Ultrasound:
A
Is a transverse wave
B
Can pass through a vacuum
C
Has a frequency greater than 20,000Hz
D
Is an electromagnetic wave of high frequency
Some practice questions
Some practice questions
Space
The moon and the earth
The moon orbits the earth. The earth’s gravity
holds the moon in orbit and stops it floating
away:
Star, Planet and moon
A star gives out it’s own energy by nuclear
reactions
A planet orbits a star, and is held in place by
the gravity of the star
A moon orbits a planet, and is held in place
by the gravity of the planet
Satellites
Artificial
satellites also
stay orbiting
the Earth due
to the Earth’s
gravity.
Comets
Comets, made of rock and dust held together by
frozen methane, also orbit the Sun (or a star).
Comets
The path of a comet
is elliptical (oval
shaped).
The tail of the comet
always points away
from the Sun and is
due to solar wind
from the Sun.
Comets
A comet goes fastest
when it is nearest the
Sun and slowest
when it is furthest
away.
Star
Orbits a planet
Planet
Produces it’s own light by a nuclear
reaction
Moon
Orbits a star
Comet
Made of rock and dust held together by
frozen methane, also orbits a star.
Exam question:
Exam question:
Exam question:
Exam question:
Exam question:
Exam question:
Our solar system
The planets orbit a star called the Sun
Space words
A collection of stars
Our galaxy
A galaxy
Universe – lots of galaxies
Another question:
Another question:
Another question:
Another question:
Life on other planets
How can we test for aliens??
One way is to test soil
samples from other
planets (like Mars).
Scientists look for
bacteria in the soil, or
even just water would
be a clue.
How can we test for aliens??
Another way is to test
for radio signals from
other planets – the
theory is that
intelligent life would
also use radio waves
and microwaves for
communication like
we do!
The life of a star like the Sun
Huge dust clouds called
nebula are attracted
in due to gravity
(particles pulling
together). The
pressure makes heat,
reaching
temperatures of 15
million degrees
centigrade.
The life of a star like the Sun
At this heat and
pressure, hydrogen
particles will combine
to make helium plus
spare energy, this is a
nuclear reaction.
The baby star is called
a main sequence star,
heated by the nuclear
reactions inside.
The life of a star like the Sun
The main sequence lasts for a hundred million years!
The life of a star like the Sun
The outer layers then expand, cool, and shine less
brightly – making a red giant.
The life of a star like the Sun
The nuclear reactions then stop and the outer gases
drift away
The life of a star like the Sun
The bit in the middle left behind is a white dwarf
The white dwarf eventually cools into a black dwarf.
Where did the universe come from
The “Big Bang” theory comes from two
observations – the universe is expanding
and the universe is cooling.
The Big Bang theory says that space was
created by an infinitely compact fireball. It
didn’t start in the universe, it WAS the start
of the universe!
Doppler shift
Doppler shift
In the same way as the pitch of a sound
wave from a car changes if it is going
towards you or away from you, the colour
of light from an object changes if the
object is moving away from you or
towards you. The light from distant
planets is more red than we would expect
(red shift) which means the planets are
moving away from us so the universe is
expanding.
The future of the universe!
If the universe is dense enough, it will slow
down expanding then start to contract due
to gravity.
If the universe is not dense enough, then
there will not be enough gravity to pull it
back in and it will keep expanding
It seems that the universe is not dense
enough to contract, so will continue to
expand for ever!
Exam question:
Exam question: