Introductions● Surveys – help me to get to know you. I wont memorise it, but it helps me to get to know you now and throughout the year.● Mind Map: What is Physics? Is it useful, and if so why? What do you know already? What would you like to learn this year?● Sculpture: Use half a packet of clay to make something which symbolises Physics.
PHYSICS● Physics is the study of the laws of the universe.● Other Sciences often apply the laws of Physics, but to think of them this way is often pointless.● Physics came out of Astronomy, which is the oldest academic discipline.● This year we will cover waves and light, electromagnetism, energy resources and radioactivity. http://en.wikipedia.org/wiki/File:CollageFisica.jpg
Housekeeping● Welcome to the last year of IGCSE Science at YIS (for everyone).● Textbooks Please keep them in your locker and bring them to class. Sometimes I will ask you to take it home for homework, and I recommend you do for revision.● Any questions?
WAVES● What are waves? What arent they? Give some examples.
WAVES A wave consists of oscillations which move without carrying matter with them. The oscillations carry energy.A wave can be used to carry the energy itself, or it can be used to carry a signal.
PulseA pulse is a single wave bump or a “disturbance”.A pulse can easily be sent down a string or spring. A wave is made of lots of regular pulses.
A Nice Animationhttp://upload.wikimedia.org/wikipedia/commons/7/7
Amplitude Amplitude determines how much energy the waves have. More amplitude = brighter light, louder sound etc. Wavelength = λ = lowercase (Greek) lambda. What is the relationship between v, f and λ?http://upload.wikimedia.org/wikipedia/commons/f/fa/Wave.JPG
Longitudinal WavesLongitudinal waves are the opposite of transverse waves.The direction of propagation is the same as the direction of vibration in the medium. https://encrypted-tbn1.google.com/ima
Example Kaoruko is swimming at a beach with waves constantly coming from the sea. She estimatesthat the distance between the wave crests is 6m,and two wave crests pass her every second. How fast are the waves travelling?
Example 2 Waltteri shouts across the room at Atsu. Heshouts with a low frequency of 5000 Hertz, andthe waves travel at a speed of 340 m/s. What is the wavelength of Waltteris voice?
Quick Review● Write a definition in your own words of: A. Frequency B. Wavelength C. Wave speed D. Amplitude E. Crest F. Trough● State and explain the wave equation, including explaining why it works.
A. What is the time period of a wave if two wavespass every twenty seconds?B. What is the frequency of the wave from A?C. Hard: what is the relationship between time periodand frequency (for any wave)? Write it like a mathequation, using f for frequency and T for time period.It is ok if you cant do this question :)
The speed of sound in air is about three hundred and forty metres persecond.10. What is the frequency of a sound wave with a wavelength of 6.8meters?11. Humans can hear approximately twenty hertz to twenty kilohertz.Calculate the minimum and maximum wavelengths humans can hear.12. The speed of light is 300 000 000 (3 * 108) meters per second.Calculate the wavelength of red light, given that it has a frequency of 500000 000 000 000 (5 * 1014) Hertz.
The Microwave● Calculate the wavelength of the microwaves in a microwave oven.
Mia is swimming in a wave pool. The wave generator creates two waves each second, andthey travel at a speed of three metres per second. A. Will Mia notice the wave crests or troughs? B. How far apart are two crests or two troughs?
Quantity Symbol Formula UnitSpeed/ V metres pervelocity s = f*λ second (m/s) f = v/λ Hertz (Hz) λ (lambda)
● Explain the difference between transverse and longitudinal waves (not done yet)● Examples: Transverse Longitudinal
Virtual Experiment Go to phet.colorado.edu/web- pages/simulations-base.html● Go to Sound and Waves. Choose “Water” (top left), “one drip” and “no barrier” (centre right).● Devise an experiment to calculate the speed of the waves in the water.
Wavefronts● A wave can be drawn as a series of lines, where each line represents a crest.● We can also draw them as a line through the middle of the wave, often called a ray.● What is the mathematical relationship between the ray and the wavefronts?
Reflection of Waves● The region two different media meet is called a boundary.● At a boundary a wave can reflect. http://science.jburroughs.org/mschober/w
Refraction of Waves● If a wave enters a different medium, its The image of speed will probably soldiers was change. from Giancoli● A change in speed Physics, sixth causes a change in edition, so direction. cannot be distributed here.● Depth of water changes the speed of waves.
Diffraction● As waves pass a barrier or through a gap in a barrier, they spread out.● The diffraction is generally only noticeable if the gap is not much larger than one wavelength. http://innovativescience.blogspot.com/
Textbook work● All questions on page 95.● Then continue with assignments.
Electromagnetic Radiation● Electromagnetic radiation is a family of waves which are made of an electric field and a magnetic field interacting with each other.● All EM Waves A. Are transverse Unnecessary B. Can travel through a vacuum images of a C. Travel at c, 3*108 m/s magnet and a Van der Graaf generator removed.
Speed, Frequency, Wavelength The velocity is always the same.● What happens to the wavelength as the frequency increases?● What happens to the frequency as the wavelength increases?● What is the mathematical relationship between frequency and wavelength?
The Electromagnetic Spectrumikipedia/commons/thumb/c/cf/EM_Spectrum_Properties_edit.svg/675pedit.svg.png
Electromagnetic Spectrum Wave Approximate Approximate Uses Frequency Wavelength Radio waves 103m Microwaves 10-2m Infra Red 10-5m Waves Visible Light 5 *10-7m Ultraviolet Light 10-8m X Rays 10-10m Gamma Rays 10-12mseeing things; for cell phones and for heating things which contain water; transmittingsignals; photographing bones which cant be seen with visible light; remote controls;identifying genuine or forged documents, and for purification of air and water; to sterilisefood and seeds, and for cancer treatment
The words seeing things; for cell phones and for heatingthings which contain water; transmitting signals; photographing bones which cant be seen withvisible light; remote controls; identifying genuine or forged documents, and for purification of air and water; to sterilise food and seeds, and for cancer treatment
Signals● Electromagnetic waves are used to carry signals.● A continuous variation is called an analog signal, whereas digital signals are represented as numbers. Most early communications devices used analogue, while most modern devices use digital (exceptions?). http://news.bbc.co.uk/2/hi/technology/61429
Radio Waves● Radio waves are used to carry signals for radio, TV and mobile phones.● Either the frequency or amplitude must be changed (modulation) to carry the signal. http://www.softwareforeducation.com/
Frequency Bands● Different frequencies (“bandwidths”) are used for different applications. They must be managed(as a resource) to ensure that people dont use the same frequency in the same place. http://en.wikipedia.org/wiki/Radio_spectrum
Absorption by the Atmospherehttp://en.wikipedia.org/wiki/File:Atmospheric_electromagnetic_opacity.svg
The Ionosphere● The ionosphere is a layer of charged particles in the upper atmosphere. Medium waves are reflected off the ionosphere, and this can be used to spread them around the Earth.● Microwaves pass through the atmosphere, and can be reflected off satellites to pass signals around the Earth. http://www.indata.com/satellite_basics.h http://yutok.blogspot.com/2007/09/broadb
AM and FM● AM radio waves can diffract around hills and mountains, so are best for rural areas.● FM signals are better quality, and are generally used in urban areas. http://scienceaid.co.uk/physics/wa
Fibre Optics ● Fibre optics are thin glass cables which carry electromagnetic radiation(IR or visible light) inside them. ● They are thinner and lighter than electrical wire, and lose less signal over long distances.http://upload.wikimedia.org/wikipedia/commons/thumb/4/49/Fibreoptic.jpg/220px-Fibreoptic.jpg
This lesson: SOUND● Sound waves● Speed of sound● Noise and vibration● Pitch and volume (=frequency and amplitude)● Pages 100-107● 10A did the bookwork but not experiment Tuesday (fire drill)● 10B Wednesday● 10C Thursday (One slide completed already)
Sound● Sound is a longitudinal wave.● It can travel through liquids and all gases.● An oscilloscope can convert sound waves to visible transverse waves.● Humans can hear from around 20 Hz to 20 kHz, and the range decreases with range. A phone can typically carry waves ranging from 300Hz to 3.4kHz.
Pitch and Loudness● Recall humans can hear from 20 Hz to 20 kHz.● Frequency = pitch● Amplitude = volumehttp://www.sciencelearn.org.nz/Contexts/Th
Frequency Ranges● Drum = 20Hz● Low note from a singer = 100Hz.● High note from singer = 1000Hz.● Whistle = 10 000 Hz. All images from wikimedia commons.
Testing Skype● Use a tone generator software (tonegen is free but expires to test the frequency response range of skype (or your microphone).
Noise and decibels (dB)● Noise is unwanted sound.● Sound level is measured in decibels (dB). http://impact.books.officelive.com/Pro
Antinoise● An antinoise plays the a opposite wave to sound in the air to cancel it out.● It is difficult because sound comes from all around and bounces off walls etc.http://www.themotorreport.com.au/5928/to
The Speed of Sound● Sound is a longitudinal wave.● Try out the following simulations: http://www.kettering.edu/physics/drussell/Demos/wa● http://www.phy.hk/wiki/englishhtm/Lwave.htm● http://www.cbu.edu/~jvarrian/applets/waves1/lontra● Sound can travel in many different media. Which properties of the medium will determine the speed of sound in it?●●
Measuring the Speed of Sound● Load logger pro and open 33 – Speed of Sound.● Formative – teacher view.● Instructions in handout.● Follow-up activities: Old IGCSE exam questions (handed out in class).
IGCSE June 2008 Question 2The number of waves per second.pitch dolphin dolphin
● The Sound of Musichttp://upload.wikimedia.org/wikipedia/commons/2/22/Octaaf0320w.JPG
Musical Notes● A simple, pure note is a sound wave of a single frequency, such as that produced by a tuning fork.● However, most things which produce sound (especially musical instruments) produce other notes, called overtones, which make notes of the same frequency sound different.● If two notes are an octave apart, one has double the frequency of the other.
LightLight is an electromagnetic wave, therefore:1) It travels at a speed of light.2) It can travel through a vacuum. 3) As a wave, it can diffract, refract or reflect.●Light can be drawn as rays, where the ray is perpendicularto the wavefronts.●Light (rays) must travel in straight lines.●The eye detects light (more later). Some things emit light(eg the sun, light bulbs) while most things we see reflect light(eg walls, mirrors, the moon.) http://commons.wikimedia.org/wiki/File:Gluehbirne_2_db.jpg
Electromagnetic Spectrum Visible light has a wavelength of approximately 400 to 750nm (_________________). Our eyes are probably sensitive to these frequencies because ____________________ _____________________.http://commons.wikimedia.org/wiki/File:Electromagnetic-Spectrum-Hebrew.png
Lasers● Laser stands for Light Amplification through Stimulated Emission of Radiation (not in IGCSE).● Laser light is all the same frequency (c________) and all in phase, meaning that the troughs and crests are all in the same place. Lasers have many uses:● Fibre optics (data)● Medical Operations● Cds/DVDs http://commons.wikimedia.org/wiki/File:Laser_show_disco_(2).jpg
Holograms A hologram is a 3D image made using lasers.They are often added to important documents and to make forgery more difficult. http://upload.wikimedia.org/wikipedia/commons/8/85/Rainbow_hologram.jpeg
Reflection of Light ● Most objects reflect light but scatter it in all directions. Mirrors (and other shiny surfaces) reflect light so that they produce images. ● Reflected rays follow two rules: ι ρ θ =θ 1. The angle of incidence equals the angle of reflection. 2. The incident ray, normal and the reflected ray all lie in the same plane. Angle of incidence Angle of reflectionhttp://upload.wikimedia.org/wikipedia/commons/b/b2/Ray_optics_diagram_incidence_reflection_and_refraction.svg
Images from Plane Mirrors● Plane mirrors form images which are: 1. the same size 2. the same distance from the mirror 3. laterally inverted (left and right swapped).● A great site below: http://www.kss.sd23.bc.ca/staff/jstracha/physics_11/course_material/unit8/U08L01/pages/ray7_
The Dog at the BeachIts probably not necessary to load the picture ofthe dog that was here :)
How the Dog Runs Sand Sea http://commons.wikimedia.org/wiki/File:2009-11-19_(31)_Branch,_Ast.JPGhttp://commons.wikimedia.org/wiki/File:Dog_retrieving_stick.jpg http://commons.wikimedia.org/wiki/File:Brittany_Spaniel_Dog.jpg
How the Dog Runs Sand Sea Sand http://commons.wikimedia.org/wiki/File:2009-11-19_(31)_Branch,_Ast.JPGhttp://commons.wikimedia.org/wiki/File:Dog_retrieving_stick.jpg http://commons.wikimedia.org/wiki/File:Brittany_Spaniel_Dog.jpg
Refraction● When light enters a different medium, it changes direction, unless it enters along the normal (an angle of incidence of ______).● As light enters a more dense medium, it slows http://www.daviddarling.info/images/refrac down, and bends ____________ the normal.● As light enters a less dense medium, it speeds up, and bends ____________ from the normal.
The Brain● Recall that the part of the brain which subconsciously controls the eye thinks that light always travels in straight lines. http://www.mikecurtis.org.uk/light3.gif
Why Something Looks Bent in Waterhttp://upload.wikimedia.org/wikipedia/commons/thumb/c/cc/Pencil_in_a_bowl_of_water.svg/1000p-Pencil_in_a_bowl_of_water.svg.png
Refraction and Colour ● High frequency light (eg violet) is bent more than low frequency light (eg red). ● This is why a prism can separate white light into its different colours. ● This process is known as dispersion.http://upload.wikimedia.org/wikipedia/commons/0/06/Prism_rainbow_schema.png
The Semi-Circular BlockWhen light is shone towards the centre ofthe (semi) circle, the angle if incidence isalways ________.
The Critical Angle is the angle for which therefracted ray has an angle of refraction of 90°.
Total Internal Reflection● When light travels from a MORE dense medium to a LESS dense medium, it bends _____ _______ the normal.● If the refracted light has an angle of refraction greater than the critical angle, the light is instead reflected. This is called total internal reflection.
Determining The Critical Angle● Determine the critical angle for perspex.● While you are using the ray boxes, also observe http://www.one-school.net/Malaysia/Unive and draw how light refracts through a rectangular perspex block, and the convex and concave lenses.
Convex Lenses A convex lens can produce a real image. A real image forms when light leaves an objectand meets somewhere else. The object appears to be where its image is.
Images An image can be: ●enlarged, diminished or the same size ●upright or inverted●real (light focusses there) or virtual (light looks like it focuses there).
Real Images A real image can be focussed onto a screen. The object appears to be where the image is. If it is bright and clear enough, a real image can trick the eye (and person) into thinking that something is really there. Ray 1: Parallel to the principle axis and Ray 2: Through the optical centre. through the focus.principle axis C F F Ray 3: Through the closest focus and then parallel to the principle axis. http://upload.wikimedia.org/wikipedia/commons/a/af/Pencil_drawing.png
Real Images A real image can be focussed onto a screen. The object appears to be where the image is. If it is bright and clear enough, a real image can trick the eye (and person) into thinking that something is really there. Ray 1: Parallel to the principle axis and Ray 2: Through the optical centre. through the focus.principle axis C F F Ray 3: Through the closest focus and then parallel to the principle axis.
Convex Lens Summary object Image Real Enlarged / Upright / Use (if any) position position /virtual Diminished Inverted / same sizeBeyond C On CBetween C and F On FBetween F and the Lens
CAMERA Film/ CCDIf the image were a very, very long way away, whatwould the distance from the lens to the film be? http://commons.wikimedia.org/w/index.php?title=File:Person_Outline_2.svg&page=1
CAMERAFilm/ CCD F At this point, the image of the man is focussed on the film.
CAMERAFilm/ CCD F When the man walks closer, the(larger) image forms behind the CCD.
CAMERAFilm/ CCD F To keep the image focussed on the CCD, the lens is moved towards the man. The image is larger, which makes sense because the object being photographed is closer.
An Excellent Site to Try Out● http://www.phy.ntnu.edu.tw/ntnujava/index.php?topi● In this simulation its possible to try many different locations for objects and images.
Concave Lenses● A concave lens is the opposite of a convex lens.● Light always diverges (spreads out).● Parallel light rays spread out as if they had come from a point called a focus. http://hyperphysics.phy-astr.gsu.edu/h● Images will always be _______, ______,and ________.● Concave lenses will not be examined in IGCSE exams.
Alternate Names● Convex lenses are also called converging lenses (because they converge light).● Concave lenses are also called diverging lenses.● Concave = “going into a cave”.
Parallel verses Non-Parallel Rays DONT FORGET ARROWS!!sun ● Objects from a long way away produce (virtually) parallel rays of light. Light rays from the sun can be considered parallel because its distance is considered to be ___________. ● Parallel light rays converge at the __________.Objects nearby produce light rays which are not parallel. Lightrays from an object of finite do will meet at a distance di. Thisdistance can be found using a ray diagram or calculations.
Lenses in IGCSE● Only diagrams for convex lenses will be examined.