Waves

Waves

1. WAVES- BASICS

   • Wavelength, Frequency, Amplitude and Speed
     • WAVELENGTH IS THE DISTANCE FROM ONE PEAK TO THE NEXT
     • FREQUENCY IS HOW MANY COMPLETE WAVES THERE ARE PER SECOND. (Hz) 1Hz IS 1 WAVE PER SECOND
       • FREQUENCY= 1/ TIME PERIOD
     • AMPLITUDE IS THE HEIGHT OF THE WAVE [REST TO CREST]
     • THE PERIOD IS THE TIME IT TAKES FOR ONE COMPLETE WAVE TO PASS A POINT
   • Formulas
     • WAVE SPEED = FREQUENCY * WAVELENGTH
   • Transverse or Longitudinal
     • TRANSVERSE WAVES HAVE VIBRATIONS WHICH ARE AT 90 DEGREES TO THE DIRECTION ENERGY IS TRANSFERRED BY THE WAVE
       • EM WAVES AND LIGHT
       • SLINKY SPRING WIGGLED UP AND DOWN
     • LONGITUDINAL WAVES HAVE VIBRATIONS THAT ARE ALONG THE SAME DIRECTION AS THE WAVE TRANSFERS ENERGY
       • SOUND AND ULTRASOUND
       • A SLINKY SPRING WHEN YOU PUSH THE END
   • TRANSFER ENERGY WITHOUT TRANSFERRING MATTER

2. WAVE BEHAVIOUR AND EM WAVES

   • Two or More Waves Moving Together Have Wave Fronts
     • WAVEFRONTS ARE IMAGINARY PLANES THAT CUT ACROSS ALL THE WAVES, CONNECTING THE POINTS ON ADJACENT WAVES ARE VIBRATING TOGETHER.
     • THE DISTANCE BETWEEN EACH WAVEFRONT IS EQUAL TO ONE WAVELENGTH
   • The Doppler Effect Makes Waves Longer or Shorter
     • WAVES PRODUCED FROM A SOURCE WHICH IS MOVING TOWARDS OR AWAY FROM AN OBSEVER WILL HAVE DIFFERENT WAVELENGTH THAN THEY WOULD IF THE SOURCE WERE STATIONARY
     • THIS IS BECAUSE THE WAVE SPEED IS CONSTANT, SO IF THE SOURCE IS MOVING, IT 'CATCHES UP' TO THE WAVES IN FRONT OF IT. THIS CAUSES THE WAVEFRONTS TO BUNCH UP IN FRONT OF THE MOVING SOURCE AND SPREAD OUT BEHIND IT.
     • THE FREQUENCY OF A WAVE FROM A SOURCE MOVING TOWARDS YOU WILL BE HIGHER AND ITS WAVELENGTH WILL BE SHORTER THAN THE WAVE PRODUCED BY THE SOURCE.
       • FASTER WAVE= LONGER WAVELENGTH
     • FREQUENCY OF A WAVE FROM A SOURCE MOVING AWAY FROM YOU WILL BE LOWER AND ITS WAVELENGTH WILL BE LONGER THAN THE WAVE PRODUCED BY THE SOURCE.
   • There are Seven Types of EM Waves
     • ALL ARE TRANSVERSE WAVES TRAVEL AT THE SAME SPEED THROUGH A VACUUM
       • DIFFERENT COLOURS OF VISIBLE LIGHT DEPENDS ON WAVELENGTH- RED= LONGEST WAVELENGTH AND LOWEST FREQUENCY AND VIOLET= SHORTEST WAVELENGTH AND HIGHEST FREQUENCY

3. USES OF EM WAVES

   • Microwaves are Used for satellite Communication and Heating Food
     • WAVELENGTHS= 1-10CM
     • SATELLITE COMMUNICATION AND PHONES AND COOKING BEING ABSORBED BY THE WATER MOLECULES IN THE FOOD. ENERGY IS CONDUCTED AND CONVECTED
     • RECIEVED BY A DISH ORBITING THOUSANDS KILOMETRES ABOVE THE EARTH AND BACK AGAIN.
   • Radio Waves are Used Mainly for Communication
     • wavelengths= >10 cm
       • TV AND FM
     • long- wave radio. wavelengths= 1-10km
     • short- wave radio= wavelength= 10m-100m
       • reflected from the ionosphere
   • Infrared Radiation is Used for Heating and to Monitor Temperature
     • KNOWN AS HEAT RADIATION.
       • GRILLS TO COOK FOOD
       • GIVEN OUT OF ALL OBJECTS. HOTTER= MORE IR RADIATION.
     • THEY ARE DETECTED BY NIGHT VISION EQUIPMENT. THEY TURN IT INTO AN ELECTRICAL SIGNAL, WHICH IS DISPLAYED ON A SCREEN AS A PICTURE TO SHOWS OBJECTS.
   • Light Signals can Travel Through Optical Fibres
     • OPTICAL FIBRES CARRY DATA OVER LONG DISTANCES AS PULSES OF LIGHT
       • THEY WORK BY BOUNCING WAVES OFF THE SIDES OF A VERY NARROW CORE
     • THE PULSE OF LIGHT ENTERS THE FIBRE AT A CERTAIN ANGLE AT ONE END AND IS REFLECTED AGAIN AND AGAIN UNTIL IT EMERGES AT THE OTHER END
       • THEY ARE USED FOR TELEPHONE AND INTERNET CABLES. THERE IS ALSO MEDICAL PURPOSES.
   • Visible light is Also useful for Photography
     • CAMERAS USES LENS TO FOCUS VISIBLE LIGHT ONTO A LIGHT-SENSITIVE FILM OR SENSOR
       • THE LENS APERTURE CONTROLS HOW MUCH LIGHT ENTERS THE CAMERA.
         • SHUTTER SPEED= HOW LONG THE FILM OR SENSOR IS EXPOSED TO THE LIGHT
   • Ultraviolet is used in Fluorescent Lamps
     • FLUORESCENCE= UV RADIATION IS ABSORBED AND THEN VISIBLE LIGHT IS EMITTED.
     • NEARLY ALL UV RADIATION IS ABSORBED BY A PHOSPHOR COATING ON THE INSIDE OF THE GLASS WHICH EMITS VISIBLE LIGHT
     • THEY ARE MORE ENERGY EFFIECIENT THAN FILAMENT LIGHT BULBS
   • X-rays let Us See Inside things
     • THEY ARE USED TO VIEW INTERNAL STRUCTURE OF OBJECTS.
       • CANT PASS THROUGH DENSER MATERIAL
     • X-RAYS ARE DIRECTED THROUGH THE BODY. BRIGHTER BITS= FEWER X-RAYS
   • Gamma radiation Can be very Useful For
     • STERILISING MEDICAL EQUIPMENT BY KILLING ALL THE MICROBES. BOILING THE EQUIPMENT MAY DAMAGE AT HIGH TEMPERATURES
     • STERILISING FOOD - KILLING THE MICROBES = FRESH FOR LONGER AND NOT RADIOACITVE

4. DANGERS OF EM WAVES

   • EM Radiation Can be Harmful to People
     • THEY MOSTLY PASSES THROUGH SOFT TISSUE WITHOUT BEING ABSORBED
     • OTHER TYPES ARE ABSORBED AND CAUSE HEATING OF THE CELLS
     • SOME CAN CAUSE CANCEROUS CHANGES IN LIVING CELLS.
   • Higher frequency EM radiation is Usually More Dangerous
     • EFFECTS DEPEND ON ITS FREQUENCY. HIGHER FREQUENCY= MORE ENERGY AND MORE HARMFUL
     • IT IS HOW RADIATIONS EFFECT HUMAN TISSUE
   • Microwaves
     • SIMILAR FREQUENCY TO THE VIBRATIONS OF MANY MOLECULES, THEY CAN INCREASE THESE VIBRATION.
     • THEY HEAT HUMAN BODY TISSUE INTERNALLY. MICROWAVE OVENS NEED TO HAVE SHIELDING TO PREVENT THIS.
   • Infrared
     • FREQUENCIES CAN MAKLE THE SURFACE MOLECULES OF ANY SUBSTANCE VIBRATE- HEATING EFFECT. IT HAS A HIGHER FREQUENCY= MORE ENERGY= SKIN BURNS
   • Ultraviolet
     • THY CAN DAMAGE SURFACE CELLS AND CAN CAUSE BLINDNESS. SOME ARE IONISING= CELL MUTATIONS OR DESTRUCTION, AND CANCER
     • SUNSCREEN WILL PROTECT YOU WITH UV FILTERS
   • Gamma
     • THEY AREIONISING AND CARRY MORE ENERGY= MORE DAMAGE AND PENETRATE FURTHER INTO THE BODY. THEY CAN CAUSE CELL MUTATION OF DESTRUCTION LEADING TO TISSUE DAMAGE OR CANCER.
     • THEY SHOULD BE KEPT IN LEAD-LINED BOXES. AND SHOULD BE EXPOSED FOR A SHORT AMOUNT OF TIME.

5. SNELL'S LAW

   • Every Transparent Material Has a Refracted Index
     • REFRACTED INDEX OF A TRANSPARENT MATERIAL= HOW FAST LIGHT TRAVELS IN THE MATERIALS
     • REFRACTED INDEX, [n] = SPEED OF LIGHT IN A VACUUM, [c] / SPEED OF LIGHT IN THAT MATERIAL [v]
     • LIGHT SLOWS DOWN IN GLASS= REFRACTIVE INDEX OF GLASS IS HIGH
       • REFRACTIVE INDEX OF WATER IS A BIT LOWER= LIGHT DOESN'T SLOW DOWN AS MUCH
     • SPEED OF LIGHT IN AIR= SAME AS VACUUM. SO REFRACTIVE INDEX OF AIR= 1.00 [2 D.P.]
   • SNELL'S LAW STATES
     • THE ANGLE OF INCIDENCE, ANGLE OF REFRACTION, AND REFRACTIVE INDEX ARE LINKED
     • [n]= SIN [i] / SIN [r]
   • Find the Refractive Index of Glass Using a Glass Block
     • DRAW AROUND GLASS BLOCK ON A PIECE OF PAPER AND DIRECT A RAY OF LIGHT THROUGH IT AT AN ANGLE. TRACE THE INCIDENT AND EMERGENT RAYS, REMOVE THE BLOCK, THEN DRAW IN THE REFRACTED RAY BETWEEN THEM.
       • YOU THEN NEED TO DRAW IN THE NORMAL AT 90 DEGREES TO THE ENDGE OF THE BLOCK, AT THE POINT WHERE THE RAY ENTERS THE BLOCK
         • USE PROTRACTOR TO MEASURE ANGLE OF INCIDENCE [I] AND THE ANGLE OF REFRACTION [r], AS SHOWN.
           • THEN CALCULATE USING FORMULA

6. CRITICAL ANGLES

   • Use Semicircular Blocks to Show Total Internal Reflection
     • KEEP INCREASING THE ANGLE OF INCIDENCE [i], THE ANGLE OF REFRACTION [r] GETS CLOSER TO 90 DEGREES
       • EVENTUALLY, I REACHES A CRITICAL ANGLE c FOR WHICH R= 90 DEGREES. ALONG THE BOUNDARY
         • ABOVE CRITICAL ANGLE, YOU GET TOTAL INTERNAL REFLECTION- NO LIGHTS LEAVES THE MEDIUM
     • EXPERIMENT
       • SEMICIRCULAR BLOCK INSTEAD OF A REGULAR ONE. THE INCIDENT LIGHT RAY IS AIMED AT THE CURVED EDGE OF THE BLOCK SO THAT IT ALWAYS ENTRES AT RIGHT ANGLES TO THE EDGE. = DOESN'T BEND AS IT ENTERS THE BLOCK, ONLY WHEN IT LEAVES FROM THE STRAIGHT EDGE
         • INVESTIGATING THE CRITICLE ANGLE, c, MARK THE POSITIONS OF THE RAYS AND THE BLOCK ON PAPER AND USE A PROTRACTOR TO MEASURE i AND r FOR DIFFERENT ANGLES OF INCIDENCE.
           • IF ANGLE OF INCIDENCE [i] IS
             • LESS THAN CRITICAL ANGLE: MOST OF THE LIGHT PASSES OUT BUT A LITTLE BIT IS INTERNALLY REFLECTED
             • EQUAL TO CRITICAL ANGLE: THE EMERGING RAY COMES OUT ALONG THE SURFACE. THERE'S A LOT OF INTERNAL REFLECTION.
             • GREATER THAN CRITICAL ANGLE: NO LIGHT COMES OUT. IT'S ALL INTERNALLY REFLECTED, I.E. TOTAL INTERNAL REFLECTION
   • You can Use Snell's Law to find Critical Angles
     • SIN c = 1/ n
       • n IS THE REFRACTIVE IDEX OF MATERIAL
       • c = CRITICAL ANGLE
       • THE HIGHER THE REFRACTIVE INDEX, THE LOWER THE CRITICAL ANGLE. WATER, c IS 49 DEGREES
   • Optical Fibres and Prisms Use Total Internal Reflection
     • OPTICAL FIBRES MADE OF PLASTIC OR GLASS CONSIST OF A CENTRAL CORE SURROUNDED BY CLADDING WITH A LOWER REFLECTIVE INDEX
     • THE CORE OF THE FIBRE IS SO NARROW THAT LIGHT SIGNALS PASSING THROUGH IT ALWAYS HIT THE CORE- CLADDING BOUNDARY AT ANGLES HIGHER THAN c- SO THE LIGHT IS ALWAYS TOTALLY INTERNAL REFLECTED. IT ONLY STOPS WORKING IF THE FIBRE IS BENT TOO SHARPLY
     • TOTAL INTERNAL REFLECTION ALSO ALLOWS US TO USE PRIMS TO SEE OBJECTS THAT AREN'T IN OUR DIRECT LINE OF SIGHT. THIS IS HOW A PERISCOPE WORKS
       • THE RAY OF LIGHT TRAVELS INTO ONE PRISM WHERE IT IS TOTALLY INTERNALLY REFLECTED BY 90 DEGREES
         • IT TRAVELS TO ANOTHER PRISM LOWER DOWN AND IS TOTALLY INTERNALLY REFLECTED BY ANOTHER 90 DEGREES
           • IT IS NOW TRAVELLING PARALLEL TO ITS INITIAL PATH BUT AT A DIFFERENT HEIGHT

7. SOUND WAVES

   • Sound Travels as a Wave
     • SOUND WAVES ARE LONGITUDINAL CAUSED BY VIBRATING OBJECTS. THESE ARE PASSED THROUGH THE SURROUNDING MEDIUM AS ASERIES OF COMPRESSIONS
     • SOUND MAY REACH SOMEONE'S EARDRUM- HUMAN CAN HEAR FREQUINCIES BETWEEN 20 Hz AND 20000 Hz.
     • DENSER MATERIAL= FASTER SOUND TRAVELS THROUGH IT. IT CANT TRAVEL THROUGH A VACUUM- NO PARTICLES.
     • SOUND TRAVELS FASTER IN SOLIDS THAN IN LIQUIDS, AND FASTER IN LIQUID THAN IN GASSES
     • SOUND WAVES WILL BE REFLECTED BY HARD FLAT SURFACES. THINGS LIKE CARPETS AND CURTAINS ACT AS ABSORBING SURFACES, WHICH WILL ABSORB SOUNDS RATHER THAN REFLECT THEM.
       • THEY WILL ALSO REFRACT AS THEY ENTER DIFFERENT MEDIA. AS THEY ENTER DENSER MATERIAL, THEY SPEED UP.
   • An Oscilloscope Can Display Sound waves
     • THE MICROPHONE CONVERTS THE SOUND WAVES TO ELECTRICAL SIGNALS. USING AN OSCILLOSCOPE
     • OSCILLOSCOPE CAN TRACE THE WAVES ON SCREEN
     • THE APPEARANCE OF THE WAVE SHWS IF IT IS LOUD OR QUIET, AND HIGH OR LOW- PITCHED.
       • DETAILED MEASUREMENTS TO CALCULATE THE FREQUENCY OF THE SOUND BY ADJUSTING THE SETTING OF THE DISPLAY
   • Loudness Increases with Amplitude
     • GREATER THE AMPLITUDE= MORE ENERGY IT CARRIES = LOUDER= TRACE A LARGER AMPLITUDE ON AN OSCILLOSCOPE
   • The Higher the Frequency, the Higher the Pitch
     • FREQUENCY IS THE NUMBER OF COMPLETE VIBRATIONS EACH SECOND, AND ITS MEASURED IN Hz- 1 Hz IS EQUAL TO 1 VIBRATION PER SECOND
     • COMPARE THE FREQUENCY OF WAVES ON AN OSCILLOSCOPE- MORE COMPLETE CYCLES DISPLAYED ON THE SCREEN, THE HIGHER THE FREQUENCY
     • HIGH FREQUENCY= HIGH-PITCHED- MOUSE
       • LOW FREQUENCY= LOW-PITCHED- COW
   • Find the Period of a Wave on an oscilloscope to get its Frequency
     • HORIZONTAL AXIS= TIME
       • TIME BETWEEN EACH DIVISION CAN BE ADJUSTED TO BE CLEARER.
         • TO SHOW AT LEAST ONE COMPLETE CYCLE
           • FREQUENCY= 1/ PERIOD
   • You Can Use an Oscilloscope to Measure the Speed of Sound
     • ATTACH A SIGNAL DETECTOR TO A SPEAKER= GENERATING SPECIFIC FREQUENCIES. ADD TWO MICROPHONES AND AN OSCILLOSCOPE TO FIND WAVELENGTHS
     • DETECTED WAVES AT EACH MICROPHONE CAN BE SEEN AS A SEPERATE WAVE ON THE OSCILLOSCOPE.
       • START WITH BOTH MICROPHONES NEXT TO THE SPEAKER, SLOWLY MOVE ONE AWAY UNTIL THE TWO WAVES ARE ALIGNED ON DISPLAY, BUT EXACTLY ONE WAVELENGTH APART
         • MEASURE DISTANCE BETWEEN MICROPHONES= WAVELENGTH
           • SPEED= FREQUENCY * WAVELENGTH.
             • SPEED OF SOUND IN AIR= 340 M/S
             • FREQUENCY= SETTING OF SIGNAL GENERATOR

8. REFLECTION AND REFRACTION OF WAVES

   • Waves Can be Refracted
     • Ray Diagrams
       • Rays Passing Through a Glass Block are Refracted Twice.
         • SOME GETS REFLECTED BUT MOST GETS REFRACTED
           • AS IT HITS THE BLOCK LIGHT PASSES THROUGH A DENSER MEDIUM SO IT SLOWS DOWN
             • THEN ON THE OTHERSIDE IT PASSES THROUGH A LESS DENSE MEDIUM WICH SPEEDS THE RAY UP SO IT BENDS AWAY FROM THE NORMAL
       • IF THE MATERIAL IS DENSER IT BENDS TOWARDS THE NORMAL [MIRROR] = SMALLER ANGLE OF REFRACTION THEN INCIDENCE
     • WHEN A WAVE CROSSES A BOUNDARY BETWEEN TWO SUBSTANCES, FROM GLASS TO AIR, IT CHANGES SPEED
     • WAVES RAVEL AT DIFFERENT SPEEDS IN SUBSTANCES WHICH HAVE DIFFERENT DENSITIES. EM WAVES TRAVEL SLOWER IN DENSER MEDIA.
       • SOUNDWAVES FASTER IN DENSER SUBSTANCES
   • Reflection of Light Lets Us See Things
     • LAW OF REFLECTION
       • ANGLE OF INCIDENCE= ANDLE OF REFLECTION
         • REFLECTION= REFLECTED WAVE.
         • INCIDENCE= INCOMING WAVE
     • VIRTUAL IMAGES ARE FORMED WHEN THE LIGHT RAYS BOUNCING OFF AN OBJECT ONTO A MIRROR ARE DIVERGING= OBJECT LOOKS LIKE IT IS FROM A DIFFERENT PLACE
     • REFLECTION ALLOWS US TO SEE THINGS- LIGHT BOUNCES OFF AND TOO OUR EYES.
       • UNEVEN SURFACE [PAPER]= DIFFUSE REFLECTION.
         • EVEN SURFACE [MIRROR]= CLEAR REFLECTION
     • VISIBLE LIGHT= TRANSVERSE WAVE.

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