Module 6: Waves, atoms and space

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Units

6.01 Units

Waves

6.02 Longitudinal and transverse waves
Energy travels around as vibrations called waves.  Sound and light energy travel this way. 
 
A transverse wave must travel in a substance like air or water.  Parts of the substance move backwards and forwards.  Some are compressed but other parts are spread out.
|||| | |  |  |  | | | |||| | | |  |  |  | | | ||||         ---> movement of substance and energy --->
<-----------> = wavelength      Number of waves passing in one second = frequency.
amplitude is how far one bit of the substance moves forwards and backwards.

A longitudinal wave can travel in a substance but also in a vacuum.
~~~~~~~ movement of energy --->  movement of substance up and down^
->   <--  = wavelength, frequency = number of waves per second, amplitude=distance from middle of wave to the top.

6.03 The electromagnetic spectrum
The spectrum contains 
gamma rays, X-rays, ultraviolet UV, visible light, infra-red IR, microwaves, and radio waves

6.04 The order of the electromagnetic spectrum
radio, microwave, infra-red, visible, ultraviolet, X-rays, gamma
long wavelength                                            short wavelength
low frequency                                               high frequency                      
visible light: red, orange, yellow, green, blue, indigo, violet
           low frequency                                 high frequency
           short wavelength                             long wavelength

6.05 The energy, danger and frequency of electromagnetic waves
The danger of a wave increases as its energy and frequency increase.

6.06 The type and speed of electromagnetic waves
All electromagnetic waves are transverse.  In a vacuum these waves travel at 
300 000 000m/s.  The speed changes slightly if the waves travel through a substance.

6.07 Analogue and digital signals
Information (a signal) can be carried on a wave by changing the frequency or amplitude.  This is called an analogue signal.  Music is carried on a sound wave like this.  The information can be distorted easily with an analogue signal.
A signal can also be carried by switching the wave on or off.  This is called an analogue signal.

6.08 Uses of electromagnetic radiation

Science theory 6.08

6.09 The effects of electromagnetic waves on the body
All electromagnetic waves can heat the body.  The more energy the bigger the effect.  Larger amounts of energy can cause burning.
Ultra violet, X-rays and gamma rays can damage cells in the body.  Ultraviolet can damage the eyes.
If they damage the nucleus of the cell then it may grow out of control and form a cancer.  If the cells damaged are sperm or egg cells then the damage is passed on to the next generation.

6.10 The path of light through glass and air
Light travels in straight lines in both air and glass.
Light changes direction when it travels from from one to the other.  This change of direction is called refraction.

6.11 Explaining the refraction of light

Light changes direction in glass because the waves slow down.  One edge of the wave slows before the other causing the front of the wave to swing around.

6.12 Optical fibres
An optical fibre is made of glass.  It carries a signal using light.  The light reflects off of the inside of the glass instead of passing through so no light and no signal is lost.  In copper cable carrying electrical signals energy is lost.


6.13 The nature of sound waves
Sound is an example of a longitudinal wave

6.14 Ultrasound and the range of frequencies for human ears
Human hearing can detect frequencies from 20Hz to 20000Hz.  Sound of higher frequencies is called ultrasound.

6.15 Ultrasound in medical imaging and echo sounding
Ultrasound is used to make some medical images because it is relatively safe.  The sound will bounce off of soft tissue like a baby in the womb.  It can be detected can used to create an image of an unborn baby.
Ultrasound sent from boats into the water below them reflects off of the sea bottom of shoals of fish.  This is useful for making maps of the sea floor or for fisshing.

Space

6.16 The Earth and other planets' moons
There are nine planets in the solar system. They are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto.  Many planets have moons and some have more than one.  A moon such a the Earth's was probably formed about the same time as the planet and circles it in an orbit.


6.17 Gravitational field strength
Gravitational field strength is the pulling force of a planet acting on 1kg of a substance.  It has the symbol g.  The size of g depends on the mass of the planet or moon.  The value of g for some objects in the solar system are Earth 9.8 N/kg, Moon 1.6N/kg, Mars 3.7N/kg, Jupiter 23N/kg.

6.18 The effects of gravitational force
The planets are all moving quickly through space but they do not move far away because of the gravitational force of the Sun pulls them back.  The result is that the planets move in roughly circular orbits.
The moon and artificial satellites launched into space by people are also moving quickly.  These too are held in place (close to the Earth) by gravitational force.

6.19 The orbit of a comet
Comets are large (e.g. 1km across) pieces of rock and ice.  They too are held by the gravitational pull of the Sun.  Their orbits are not circular.  Most of the time they are far from the Sun but every few years their orbit brings them much closer to the Sun and the Earth.  The result is that some of the ice melts and a tail of particles may be seen from Earth.


6.20 The Solar System in the Milky Way galaxy
The Universe contains millions of galaxies.  
A galaxy contains millions of stars.
The Milky Way is an example of a galaxy.
The Solar system is part of the Milky Way.
The Sun is part of the Solar system.
The Sun is an example of a star.
Draw a diagram to show the links above.

6.21 The methods used to gather evidence for life elsewhere
Observations from Earth or telescopes in orbit e.g. Hubble space telescope.  Light from distant planets can be used to look for gases like oxygen, water vapour or carbon dioxide.
Spacecraft landing on distant planets like Mars can take samples of soil, analyse them and test for chemicals from living things.  Check on the latest mission to Mars.
SETI is the search for extra terrestrial intelligence.  There is a search in progress for radio signals from space which may be being sent out by other intelligent life.  Radio waves from radio and TV broadcasts have been leaving earth for about 60 years but we have not as yet sent a deliberate strong signal to attract attention.

6.22 The evolution of small stars like our Sun
The Sun is a main sequence star.  It formed from a giant gas cloud called a nebula.  Many nebulae can be seen in space and we can observe what has happened to  stars similar to our Sun.
1.  Part of the gas nebula collapses.
2.  Protons in the gas nebula join or fuse together and a nuclear fusion reaction happens.  3.  This produces energy and the star begins to shine and is now said to be in its main sequence.
4.  When the nuclear fuel is used up the star expands, cools and becomes a red giant.
5.  Eventually gravity pulls the material together.  Contraction causes heating and the result is a white dwarf star.
6.  The star is no longer generating energy so it cools gradually stops shining and becomes a black dwarf.

6.23 The collapse of a nebula to form a star
It is gravity which causes the nebula to collapse and form a star.

6.24 Theories of the origin of the Universe
The steady state theory suggests that the universe has always been the same way and always will.  Although it is expanding new matter is appearing so that the density stays the same.
The big bang theory suggests that the Universe began at a specific time about 15 thousand million years ago in a huge explosion.  This caused matter to be pushed outwards so that the Universe is both getting larger ( and so less dense) and getting cooler.
Draw 5 spirals to show galaxies as they would appear in one part of the Universe now and as they would appear in 5 thousand million years time according to each theory.

6.25 Evidence in support of the  the ‘Big Bang’ (high tier)
The stars that we can see from Earth are more red than they should be.  There is a red shift.  The red light we see has a lower frequency than expected.  
This is an example of the doppler effect.  

This means that the stars are moving away from us and each other.  At some time in the past they must have been closer together.  In fact all of the matter at that time must have been in one place.  This was the time and the place of the big bang.
The static noise of a radio not tuned to a station is due to background microwave radiation from the universe around us.  It is thought to be energy left over from the big bang.

6.26 Mass and the future of the Universe
The expansion of the universe is slowed by gravity.  The bigger the mass of the universe the bigger the effect of gravity and the faster the expansion will slow.  Two things are possible.
(a) If the mass is big enough gravity will slow the moving stars, stop them moving and then pull them back together.  Eventually all matter will come back to one place. (the Big Crunch)
(b) If the mass is not big enough the stars will never be slowed enough to stop and the universe will just continue to expand.  Eventually it would become totally cold and dark.

Atoms

6.27 Atomic (proton) number, mass (nucleon) number and isotopes
The centre of at atom is called the nucleus.  It contains particles called protons and neutrons.  These particles are sometimes called nucleons.
The atomic number (or proton number) is equal to the number of protons in the nucleus of an atom.
The mass number (nucleon number) is equal to the number of neutrons plus the number of protons in an atom.
Isotopes are atoms of the same element which have different numbers of neutrons in their nuclei. As these are the same element the atoms all have the same number of protons.  For example hydrogen has 3 isotopes.  Each atom has 1 proton but a different number of neutrons.

Draw the nucleus in each case to show two isotopes of each of the following (atomic number given in brackets): helium(2), nitrogen(7), neon(10), sodium(11) and aluminium(13).

                                                       14
6.28 The use of symbols such as      C
                                                        6

The symbol above gives us information about the nucleus of an atom as follows.
  mass number6 protons and 8 neutrons
                       symbol
atomic number
Complete the following table:

6.29 The cause of radioactivity
Radioactivity is the breakdown of the nuclei of atoms.  This happens in some atoms in which the nucleus is unstable, that is all ready to break apart.  This may happen if it has few few or too many neutrons.  This breakdown of a nucleus can happen at any time and we cannot know when this will be.  It is a random process.

6.30 Types of radiation

6.31 The properties and uses of radiation

Smoke alarms
The alarm has a chamber containing a source of alpha radiation.  This source is an isotope of americium.  The alpha radiation cannot get out of the chamber so does not cause a danger.  The radiation creates ions in the chamber which allow a current to flow.  When smoke particles get in they are attracted to the ions which no longer move around easily so stopping the current.  The fall in current is detected and causes the alarm to sound.

Thickness detection
Metal sheets must be rolled to an exact thickness.  Gamma radiation is passed through the sheets as they are made.  The amount of radiation detected on the other side depends on the thickness of the metal.  The signal from the radiation detector controls a set of rollers which in turn affect the the thickness of the metal sheet.

Sterilising medical equipment
In hospitals all equipment must be clean of microbes.  Radiation kills microbes.  Instruments to be used in operations can be put into a container and gamma radiation passed over them.  They instruments do not become radioactive but all of the microbes are killed.

6.32 Background radiation
Radiation is passing through us all of the time.  This is called background radiation.
This radiation comes from many places.

6.33 The dangers of ionising radiations
Radiation is dangerous because is causes cells in our body to be damaged.  Radiation causes molecules in the cells to become charge particles call ions.  This is called ionisation.

6.34 The problems of safe disposal of radioactive waste

Radioactive waste is produced by hospitals, general industry and the nuclear industry.
The waste must be kept safe away from people and stopped from getting back into the environment through the water supply.  Some waste remains radioactive for thousands of years.
Low level waste like contaminated clothing is stored in sealed drums underground.
High level waste like nuclear power station waste must be stored in steel and concrete containers and may need to be cooled.
Radioactive waste from hospitals is often low level waste.