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Unit 1 – Universal Physics. (EdExcel). Topic 1 – Visible Light and the Solar System. Our understanding of the universe.
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Unit 1 – Universal Physics (EdExcel)
Our understanding of the universe Up until the 16th Century people believed that the Earth was the centre of the universe – this is called the “Geocentric model” and I made a model of the universe based on it. Ptolemy, AD 90-168 I published my “On the revolutions of the celestial spheres” just before my death and showed that the Earth and other planets orbit around the sun – the “Heliocentric model”. Copernicus, 1473-1543
Evidence for the Heliocentric Model I helped develop the modern telescope and made measurements with it that proved that the Copernican model of the solar system was correct. Galileo, 1564-1642 Jupiter and its moons, as seen through a telescope The orbits of these moons
Observing the Universe What are the advantages and disadvantages of each of these methods? A complex digital camera will be in here
An introduction to Waves A Wave is a “movement of energy” but NOT a transfer of matter
Wave definitions… 1) Amplitude – this is “how high” the wave is: 2)Wavelength ()– this is the distance between two corresponding points on the wave and is measured in metres: 3) Frequency – this is how many waves pass by every second and is measured in Hertz (Hz) 4) Speed – this is how fast the wave travels and is measured in metres per second (m/s)
Transverse vs. longitudinal waves Displacement Direction Direction Displacement Transverse waves are when the displacement is at right angles to the direction of the wave. Examples – light, other EM waves, some seismic waves Longitudinal waves are when the displacement is parallel to the direction of the wave… Examples – sound, some seismic waves
Refraction through a glass block: Wave slows down and bends towards the normal due to entering a more dense medium Wave speeds up and bends away from the normal due to entering a less dense medium Wave slows down but is not bent, due to entering along the normal
Refraction Refraction is when waves ____ __ or slow down due to travelling in a different _________. A medium is something that waves will travel through. When a pen is placed in water it looks like this: In this case the light rays are slowed down by the water and are _____, causing the pen to look odd. The two mediums in this example are ______ and _______. Words – speed up, water, air, bent, medium
Lenses When light enters a MORE DENSE medium it slows down… A prism uses this idea to split light. This happens because purple light is refracted more than red light Lenses use the idea of refraction:
Another example: The lens in the eye is used to focus what we see:
Converging and diverging lenses CONVERGING (Convex) Thickest at the centre DIVERGING (Concave) Thinnest at the centre
Ray diagrams for lenses 1 A “distant object” Focal length The rays of light are refracted INWARDS and meet at the focus, F. The image formed is REAL – in other words, it can be seen on a screen F The rays of light are refracted OUTWARDS. A VIRTUAL image is formed – in other words, the image doesn’t actually exist F
Lenses in Telescopes Objective lens (convex) Focal point Eyepiece lens Because stars are very far away, the rays of light from them enter a telescope effectively parallel: The objective lens basically gathers as much light as possible from the distant star and focuses it inside the telescope. The eyepiece lens then magnifies this image into the eye.
Mirrors in Telescopes Eyepiece lens Objective lens (convex) Concave mirror Flat mirror Astronomical telescopes tend to use large concave mirrors as well as a convex lens. This allows them to collect more light:
The Wave Equation V f All E-M waves obey the Wave Equation: Wave speed (v) = frequency (f) x wavelength () in m/s in Hz in m
Some example wave equation questions • A water wave has a frequency of 2Hz and a wavelength of 0.3m. How fast is it moving? • A water wave travels through a pond with a speed of 1m/s and a frequency of 5Hz. What is the wavelength of the waves? • The speed of sound is 330m/s (in air). When Dave hears this sound his ear vibrates 660 times a second. What was the wavelength of the sound? • Purple light has a wavelength of around 6x10-7m and a frequency of 5x1014Hz. What is the speed of purple light? 0.6m/s 0.2m 0.5m 3x108m/s
Distance, Speed and Time for waves Speed = distance (in metres) time (in seconds) D S T • A water wave travels 200 metres in 40 seconds. What is its speed? • Another wave covers 2km in 1,000 seconds. What is its speed? • Sound travels at around 330m/s. How long does it take to travel one mile (roughly 1,600m)? • Light travels at a speed of 300,000,000m/s. How long would it take to travel around the world if the diameter at the equator is around 40,000km?
The Visible Spectrum In the 17th Century I did lots of work on light and wrote about how visible light was made of the colours of the spectrum. I accidentally discovered that, if you put a thermometer here, it gets hot. I discovered Infra Red radiation!! Isaac Newton, 1643-1727 I then discovered ultra violet by observing how salts made from silver were lightened by something just beyond violet light. William Herschel, 1738-1822 Wilhelm Ritter, 1776-1810
Electromagnetic Radiation E-M radiation is basically a movement of energy in the form of a wave. Some examples:
The Electromagnetic Spectrum High frequency, _____ wavelength Low frequency, _____ (high) wavelength γ Each type of radiation shown in the electromagnetic spectrum has a different wavelength and a different frequency: Each of these waves travels at the same speed through a _______ (300,000,000m/s), and different wavelengths are absorbed by different surfaces (e.g. infra red is absorbed very well by ___________ surfaces). They all travel as _____ waves. The more dangerous waves are at the high ________ end of the spectrum. Words – black, transverse, long, short, vacuum, frequency
The Electromagnetic Spectrum Type of radiation Uses Dangers Treating cancer, sterilisation Gamma rays Cell mutation X rays Medical, airport scanners Cell mutation Ultra violet Sun beds, security Skin cancer None (unless you look at the sun) Seeing things, photos Visible light Remote controls, heat transfer, optical fibres Infra red Skin burns Microwaves Satellites, phones Heating of cells TV/radio Communications Very few
Introduction to Radioactivity Some substances are classed as “radioactive” – this means that they are unstable and continuously give out radiation: Radiation The nucleus is more stable after emitting some radiation – this is called “radioactive decay”. Radiation like this can be either alpha, beta or gamma radiation.
Ionisation Radiation is dangerous because it “ionises” atoms – in other words, it turns them into ions by “knocking off” electrons: Ionising radiation is emitted by radioactive sources all the time. Ionisation transfers energy to cells in living tissue, causing them to mutate, usually causing cancer.
Space: An introduction OUR SUN is one of millions of stars that orbit the centre of… THE MILKY WAY, which is one of a billion galaxies that orbit AND move away from the centre of… THE UNIVERSE, made up of everything!!
Distances in space The Sun, our closest star, is 1.6x10-5 light years away from us. The next closest star, Proxima Centauri (4.2 light years away) The centre of our galaxy, the Milky Way, is around 26,000 light years away. The Andromeda Galaxy (our closest galaxy) – approximately 2.5 million light years away
Observing the Universe Radio telescopes Space-based telescopes Consider different types of telescope: The original telescopes were used purely for visible light. These days, telescopes pick up a wide range of waves. Some examples...
Hubble Space Telescope (HST) • Launched in 1990, due to finish operating in 2010 • Takes images in the visible light, ultra-violet and near infra red regions • Orbits the Earth every 97 minutes
Infra Red Astronomical Satellite (IRAS) • Surveys infra red patterns in space • Launched in 1983 and operated for 11 months • The number of known astronomical bodies was increased by 70% due to infra red observations
Cosmic Background Explorer (COBE) • Operated from 1989 to 1993 • Detected small ripples in the Cosmic Microwave Background Radiation (CMBR) reaching the Earth
Life on Other Planets Research task Is it likely that other planets in our solar system could have life? Explain your answer. Extend your inquiry to other solar systems – what criteria must be met in order for a planet to potentially have life on it?
Searching for Aliens Humans have been searching for me for over 50 years. Here are some of the methods they use: SETI – The Search for Extra Terrestrial Intelligence Since 1960 a group of astronomers have collectively been sending out EM signals hoping that someone will send one back! Space probes The Voyager 1 probe, still in operation after over 33 years and still sending signals back to Earth. Soil samples What are the advantages and disadvantages of each of these methods? Soil samples from the moon and, in recent years, from Mars have been sampled.
How modern telescopes have helped Due to technological advances in telescopes our knowledge of the universe has been expanded. Some examples: 1) In 1610 I used a telescope to determine the existence of a galaxy around us – the Milky Way – due to better magnifications in my telescope. 2) Some stars don’t emit visible light, so they are “seen” by taking infra red photos and then applying “false colour”: Galileo 3) The Hubble Space Telescope has been able to take measurements to more accurately determine the age of the universe – around 14 billion years.
Observing the Universe Ground-based telescopes Space-based telescopes Consider different types of telescope: What are the advantages and disadvantages of each?
Benefits of observing above the atmosphere Ground-based telescopes Clearly, ground-based telescopes are a problem because of a number of things: • The amount of light absorbed by the atmosphere • Bad weather • Light is refracted, diffracted and scattered by the atmosphere (causing stars to “twinkle”)
Stage 1: Nebulae A nebulae is a collection of dust, gas and rock. Some examples of nebulae…
