waves, and space edexcel module 6 some pictures from m hancock, chapter school
TRANSCRIPT
Waves, and space
EDEXCEL Module 6
Some pictures from www.gcse.com
M Hancock, Chapter School
Waves• A Transverse wave is where the vibrations are at
right angles to the direction the wave is travelling in
Waves
• Longitudinal waves are when the vibrations are in the same direction the wave is travelling in:
WavesThe 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.
WavesThe 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.
The electromagnetic spectrumThe 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)
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 speedB The same speed and a lower frequencyC The same wavelength and a higher speedD The same speed and a higher frequency
Exam question:
Compared to X-rays, radio waves have:A A longer wavelength and higher speedB The same speed and a lower frequencyC The same wavelength and a higher speedD 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 spectrumUltraviolet light is used for sunbeds, security marking,
fluorescent lamps and detecting forged bank notes
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
Too much radiation
An overdose of ultraviolet can lead to damage to surface cells (including skin cancer) and eyes
More on ultrasoundUltrasound 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.
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 refracts away from the normal.
The normal is a line at 90o to the surface of the glass or water where the light hits it.
Another question:
Which of the following always changes when light is refracted:A The directionB The speedC The frequencyD The colour
Another question:
Which of the following always changes when light is refracted:A The directionB The speedC The frequencyD The colour
RefractionWhen 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 fibresVisible 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
CDeflection
DDiffraction
Light changes speed when it goes from air to glass.
This is called:
A Reflection
B Refraction
C Deflection
D Diffraction
Some practice questions
Some practice questions
Ultrasound:A Is a transverse waveB Can pass through a vacuumC Has a frequency greater than 20,000HzD Is an electromagnetic wave of high frequency
Some practice questions
Ultrasound:A Is a transverse waveB Can pass through a vacuumC Has a frequency greater than 20,000HzD Is an electromagnetic wave of high frequency
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
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.
Star Orbits a planet
PlanetProduces it’s own light by a nuclear reaction
Moon Orbits a star
CometMade of rock and dust held together by frozen methane, also orbits a star.
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 outer layers then expand, cool, and shine less brightly – making a red giant.
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 shiftIn 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!