Waves, and space EDEXCEL Module 6 Some pictures from M Hancock, Chapter School

space waves

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:

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: ASpeed BFrequency CWavelength DColour

Exam question: Some infra-red and ultraviolet waves travel from the Sun to Earth. In space, they all have the same: ASpeed BFrequency CWavelength DColour

Exam question: Compared to X-rays, radio waves have: AA longer wavelength and higher speed BThe same speed and a lower frequency CThe same wavelength and a higher speed DThe same speed and a higher frequency

Exam question: Compared to X-rays, radio waves have: AA longer wavelength and higher speed BThe same speed and a lower frequency CThe same wavelength and a higher speed DThe 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:

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

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 90 o 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: AThe direction BThe speed CThe frequency DThe colour

Another question: Which of the following always changes when light is refracted: AThe direction BThe speed CThe frequency DThe 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: AReflection BRefraction CDeflection DDiffraction

Light changes speed when it goes from air to glass. This is called: AReflection BRefraction CDeflection DDiffraction Some practice questions

Ultrasound: AIs a transverse wave BCan pass through a vacuum CHas a frequency greater than 20,000Hz DIs an electromagnetic wave of high frequency

Some practice questions Ultrasound: AIs a transverse wave BCan pass through a vacuum CHas a frequency greater than 20,000Hz DIs an electromagnetic wave of high frequency

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.

StarOrbits a planet Planet Produces it’s own light by a nuclear reaction MoonOrbits a star Comet Made of rock and dust held together by frozen methane, also orbits a star.

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:

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

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: