# Physics 1.

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• Created by: Abbs11_
• Created on: 26-08-16 20:28
• Physics 1.
• Visible light and the solar system.
• Most ancient Greek astronomers believed that Sun, Moon, planets and stars all orbited the Earth in perfect circles - this is known as the geocentric model.
• The heliocentric model states that the earth and planets all orbit the sun, which is at the centre of the universe.
• Copernicus introduced the heliocentric model in a book in 1543.
• In 1610 Galileo was observing Jupiter using a telescope and discovered that there were moons orbiting Jupiter. This showed that not everything was in orbit around the Earth - which proved the Geocentric model was wrong.
• Wavelength is the distance from one peak to the next.
• Frequency is how many complete waves there are per second.
• Amplitude  is just the height of the wave.
• The speed is how fast it goes.
• In traverse waves the vibrations are at 90 degrees to the direction of travel of the wave.
• In longitudinal waves the vibrations are along the same direction as the wave is travelling.
• The angle of reflection is the same as the angle of incidence.
• The lights reflected because of the change in density - water is denser than air.
• Converging lenses are used to focus light, it is convex - it bulges outwards. It causes parallel rays of light to coverage to a focus.
• An incident ray parallel to the axis will pass through the focal point when its reflected.
• An incident ray passing through the focal point will be parallel to the axis when its reflected.
• The electro-magnetic spectrum.
• Seven types of electro-magnetic waves.
• Long wave radio (wave-lengths of 1-10km) can be transmitted from all over the world.
• Radio waves used for tv and fm radio have very short wave-lengths (10cm-10m), to get reception you must be in direct sight of the transmitter.
• Short wave radio signals (wave-lengths of about 10m-100m) can be received at long distances from the transmitter.
• Thats because they are reflected from the ionosphere - an electrically charged layer in the earths upper atmosphere
• Micro waves are used for satellite comm-unication and mobile phones.
• For satellite TV the signal from a transmitter is transmitted into space.
• Where its picked up by the satellite receiver dish orbiting thousands of kilometres about the Earth.
• The satellite transmits the signal back to Earth in a different direction.
• Where its received by a satellite dish on the ground or a mobile phone.
• Microwave ovens use a different microwave wave - length from satellites.
• The  microwaves used in microwave ovens penetrate up to a few centimetres into the food before being absorbed by water molecules.
• The energy from the absorbed microwaves causes the food to heat up. The heat energy is then conducted or convected to other parts of the food.
• Micro-waves can heat human body cells. There is a suggested link with brain tumours but nothing has been proved.
• Infra red radiation can be used to monitor temp-erature.
• IR is also known as heat radiation, its given out by all hot objects - the hotter the object the more IR.
• IR is also detected by night vision equipment. The equipment turns it into an electrical electrical signal, which is displayed on a screen as a picture.
• Optical fibres can carry data over long distances as pulses of infrared radiation. e.g. in telephone cables.
• They work by bouncing waves off the sides of a thing inner core of glass or plastic. The wave enters one end of the fibre and is reflected repeatedly until it emerges at the other end.
• Other uses for IR include; Grills and toasters, remote controls, to transmit data between mobile phones and computers but only over short distances, also used in burglar alarms and security lights.
• iR also has a heating effect but has a high frequency and carries more energy than MW's so IR can cause skin burns.
• Visible light allows us to see.
• When light enters the eye it gets refracted through the lens and focused onto the retina at the back of the eye
• The retina then sends messages to the brain via the optic nerve and the brain interprets them.
• Ultraviolet.
• UV has more energy and a higher frequency than IR. UV can cause cell mutation or destruction,skin cancer, UV sunlight can also cause eye damage.
• Fluo-rescence is a property of certain chemicals, where ultraviolet radiation is absorbed and the visible light is emitted.
• UV can detect forged bank notes.
• Fluorescent lamps use UV radiation to emit visible light, they're safe to use as all the UV radiation is absorbed by a phosphor coating on the inside of the glass.
• Security pens can be used to mark your property with your name. The ink in the pen is only visible in UV light - this helps the police identify your property if its stolen.
• UV radiation can also be used to disinfect water, the UV in kills off any viruses or bacteria in the water, making it safer to use.
• X-Rays.
• Very high frequency waves, carries much more energy than UV rays. This means they are much more damaging as they can penetrate much further into the body.
• They can cause cell mutation or destruction leading to tissue damage or cancer.
• X-rays pass easily through flesh but not so easily through denser material like bones or metal. So its the amount of radiation thats absorbed that gives you an X-ray image.
• X-rays are used at hospitals by radio-graphers and also at  airports for checking luggage and passengers for un-authorised items.
• Gamma rays.
• Very high frequency waves, carries much more energy than UV rays. This means they are much more damaging as they can penetrate much further into the body.
• They can cause cell mutation or destruction leading to tissue damage or cancer.
• Is one of the three types of ionising radiation.
• Gamma rays are used to treat cancer through radio-therapy.
• Gamma is also used to sterilise food and medical instruments
• The advantage of irradiation over boiling is that it doesn't involve high temp-eratures.
• So  things like fresh apples or plastic instruments can be totally sterilised without being damaged.
• Waves and the universe.
• The Suns radius is 696,000km and the Suns mass is 1.99 x 10*30kg.
• The Earths radius is 6378km and the Earths mass is 5.97 x 10*24kg.
• The moons radius is 1738km and the Moons mass is 7.35 x 10*22kg.
• It takes light about 500 seconds to reach us on Earth from the Sun.
• Spectro-meters work by a telescope directing a beam of light into the spectro-meter and though a slit. This diffracts the light and splits it up into a spectrum.
• The light spectra from stars and galaxies contain dark lines.
• These dark lines are caused by the light at those wave-lengths being absorbed e.g. by elements in the stars atmo-sphere. These patterns of dark lines are called absorption spectra
• Absorption spectra can be used to work out what the stars and galaxies are made of - each element has its own particular absorption spectrum.
• Some spectra have bright lines - these are emission spectra. The lines are caused by extra light being emitted at those wave-lengths.
• Emission spectra can also be used to work out what something is made of.
• The spectra for galaxies further way appear more red than they should.
• When we look at light from distant galaxies we find that the frequencies are all lower than they should be - they're shifted towards the red end of the spectrum.
• Measure-ments of redshift suggest that all the galaxies are moving away from us very quickly.
• More distant galaxies have greater red-shifts than nearer ones.
• This means that more distant galaxies are moving faster than nearer ones.
• Red shift provides evidence that the whole universe is expanding.
• Telescopes.
• The first space telescope (called Hubble) was launched by NASA in 1990. It can see objects that are about a billion times fainter than you can see unaided from Earth.
• X-ray telescopes are a good way to see violent, high temp-erature events in space, like exploding stars.
• Radio telescopes were responsible for the discovery of cosmic microwave back-ground radiation.
• Scientists have detected low frequency electro-magnetic radiation coming from all parts of the universe.
• This radiation is mainly in the microwave part of the EM spectrum. Its known as the cosmic microwave back-ground radiation.
• CMB radiation is strong evidence for an initial big band, and as the universe expands and cools, this back-ground radiation 'cools' and drops in frequency.
• Modern telescopes often work alongside computers.
• Computers help create clearer and sharper images.
• Computers make it possible to collect and store huge amounts of data, 24 hours a day.
• Waves and the Earth.
• Ultrasound.
• Electrical devices can be made which produce electrical oscillations of any frequency.
• These can easily be converted into mechanical vibrations to produce sound waves beyond the range of human hearing (frequ-encies above 20,000HZ).
• Ultrasound is used for prenatal screening of a foetus.
• Ultrasound waves can pass through the body, but whenever they reach a boundary between two different media some of the wave is reflected back and detected.
• The exact timing and distribution of these echoes are processed by a computer to produce a video image of the foetus.
• Ultrasound is used for Sonar.
• Boats and submarines use sonar to detect stuff in the water around them.
• They emit waves of ultra sound which reflect of things like other boats, the sea bed and marine animals and detect these reflected waves as they arrive back at the boat.
• Computers on board time the delay between emitting the waves and detecting their reflections, and then calculate how far away they are.
• Infrasound is sound with frequencies less than 20hz.
• Infrasound has long wave lengths, they travel long distances and diffract easily.
• Infrasound is used to detect animal movements meteor strikes, volcanic eruptions and monitoring animal movements.
• P-waves are longitudinal and travel through solids and liquids. They travel faster than S-waves.
• S-waves are tranSverse they only travel through solids. They're slower than P-waves.
• Generation & trans-mission of electricity.
• Electric current and power.
• Current is the rate of flow of charge around a circuit.
• Electrons usually carry the charge - they're negatively charged particles.
• Voltage (P.D) is an electrical pressure giving a measure of the energy transferred.
• Electrical power is the energy transferred per second.
• The four factors that affect the size of the induced voltage and current.
• The strength of the magnet.
• The area of the coil.
• The number of turns on the coil.
• The speed of movement.
• Non-renewable energy resources: coal, oil, natural gas, nuclear fuels; uranium, plutonium.
• Renewable resources: hydro-electricty, wave power, tidal barrages, wind power, solar power, geothermal energy, and biomass.
• Payback time = initial cost /  annual saving.
• Energy and the future.
• Types of energy.
• Electrical energy.
• Light energy.
• Sound energy.
• Kinetic energy.
• Nuclear energy.
• Thermal energy.
• Gravi-tational potential energy.
• Elastic Potential energy.
• Chemical energy.
• Energy can never be created nor destroyed its only ever transferred from one form to another.
• Efficiency =  useful energy output / total energy input x 100%
• Leslies cube: The matte black side emits most heat, so its that thermo-meter which gets hottest.
• Dark matte surfaces absorb heat radiation falling on them much better than bright and glossy surfaces.
• Silver surfaces reflect nearly al heat radiation falling on them.
• Survival blankets: A silver coloured blanket helps to stop their body heat radiating away.