physics

  • Created by: erinl.ee
  • Created on: 03-05-19 09:15

Transverse waves

Modern communicatons involving technology:

  • phone
  • email
  • radio
  • tv
  • social media

In scientific work, modern technology is used to make and record observations, to produce these communications and broadcasting systems. 

The transverse waves travel perpendicular tp the direction of travel. They can also go through a vaccum.

**speed of light: 3 x 108 ms-1

**transfers energy, not matter

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Electromagnetic Spectrum

Real Men Ignore Very Ugly eX Girlfriends.

Radiowaves: radio broadcasting, satelight, TV (long distance communications)

Microwaves: cooking, mobile phone, communication, satelight (long distance communications)

Infrared radiation: thernmal detector, TV remotes (short distance communications)

Visible light: to see, photography, illumination (short distance communications)

Ultraviolet: cure gel nails, flouresent lamps, criminal investigations, sun beds, airports 

X-rays: bone fractures, airport security 

Gamma rays: radiotherapy, sterilising food and surgical equipment. 

Alpha= He2n2p+2               Beta= e=-1             Gamma= 0

Gamma is ionising- meanig that it can change the structure of our cells.

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Transverse waves

Image result for transverse wave

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Longitudinal waves

Image result for longitudinal wave

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Longitudinal waves

A longitudinal wave travels parallel to the direction of travel. 

They are much slower than transfers waves.

There are parts of compression (close together) and rarefraction (spread out).

Sound travels through air at the speed of 340ms-1 and in water at 1600ms-1.

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Infra and ultra sound

Infrasound is the lowest sound a human ear can pick up, certain condition can make infra sound audible. The frequecy of this is 20Hz. It has been reported to cause a feeling or fear. A use of infra sound is: theraputic devices, monitoring activities of the atmosphere and forecasting natural disasters. This is a longitudinal wave. 

Ultra sound detects objects and measures distance. It is also used by vets, medicines and human medicine for ultrasounding. This is a transverse wave. 

Comparison of the waves:

A transverse wave goes through in equal integers whereas longitudinal waves have different integers and often have differents spaces.

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What is an echo?

a sound or sounds caused by the reflection of sound waves from a surface back to the listener. An echolocation is the location of objects by reflected sound. 

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Reflection and refraction

Refraction is when the glass makes the light change direction.

Image result for reflection and refraction

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Converging Vs. Diverging lenses

Image result for converging and diverging lenses

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Converging lenses

A converging lense brings light into a place called a focal point. This is where all the lights collide in s specific spot. For people who are far sighted, they need a converging lense in their glasses. This is because the curve of their eyes makes their focal point to far back for the person's brain to register. The converging lens brings the focal point further forwards so they can register what they see.

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Diverging lenses

A diverging lenses pushes light out into different directions. This means that light that would once come together, dont. For people who are near sighted, the curve of their eyes causes the light to be brought in too soon, meaning that they need a diverging lense. This is because the light that goes into the persons eyes gets pushed back further.

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Constructive and destructive waves

What is a wave: A transfer of energy through a medium without causing a distruption to the environment.

Constructive: If we put waves together, we get bigger waves. The amplitudes can be different but they have to be on the same wave length and in phase.

Destructive: If they have a wavelength or one pi out of phase and the amplitude must be the same, they cancel each other out.

The double-split experiment:

Newtons idea of light being particles suggested that a light through two slights would show as two as particles go in straight lines. Young found that they show as circles, these suggest the theory of constructive and destructive waves as the parts with no light happen because of them being out of wave length.

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Analogue vs Digital

Analogue waves are smooth and continuous. Whereas digital waves are stepping, square and discrete. 

Waves: analogue- Denoted by sine waves/ digital- Denote by square waves

Examples: analogue- human voice in air, analogue electronic devices/ digital- computures, CDs, DVDs, and other electronical devices. 

Data transmittions: analogue- subjected to deterioration by noise during trabsmittion and write and read cyle/ digital- can be noise-immune without deterioration during transmittion and write and read cycle.

Uses: analogue- suited for audio and video transmittion/ digital- suited for computing and digital electronic.

Applications: analogue- thermometer/ digital- PCs, PDAs

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Digital and Analogue waves

Digital technology has been most efficient in cellular phone industry. Analogue phones have become redundant even though sound clarify and quality was good. 

Analogue technology comprise of natural signals like human speech. With digital technology, this human speech can be saved and stored in a computure. Thus digital technolgy opens up the horizon for endless possible use.

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Analogue vs Digital

Analogue: interference with a bigger value.

Digital: has interference with no effect at all.

AM- amplitude modulated

FM- frequency modulated

DAB- digital sudio broadcast

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Electromagnetic spectrum

Radiowaves:

  • Frequency: <3 x 1011
  • Wavelength: >1mm

Microwaves:

  • Frequency: 3 x 1011 – 1013
  • Wavelength: 1mm -- 25μm

Infrared:

  • Frequency: 4 x 1014
  • Wavelength: 1mm – 750 μm

Visable Light:

  • Frequency: 4.3 x 1014 – 7.3 x 1014
  • Wavelength: 750 nm – 400 nm
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Electromagnetic Spectrum

Ultraviolet: There are frequencies just above our visible range that can be seen by bees and some other animals, which help plants grow and cause sunburn. These are ultra-violet light (UV), because the frequencies are above those of violet.

Visable light: our eyes can only detect a very small range of frequencies. These are visable light.

Infrared: you can sense frequencies just a little lower than that of red light as radiant heat warming you. These are infra-red radiation (IR).

The remaining types of radiation are named according to how they are produced. At the highest frequencies the frequency ranges for X-rays and for y-rays (gamma rays) overlap somewhat. X-rays are produced by high energy atomic electron transitions and are just a higher energy version of light and UV radiation. On the other hand, y-rays come from nuclear disintegrations and from collisions between  high energy sub-atomic particles.

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Electromagnetic spectrum

Speed of electromagnetic waves in a vacuum:

Light, and all forms of electromagnetic radiation, travel at the same speed through vacuum 2.997925 x 108 ms-1. This is a physical constant value that is usually denoted by the letter, C.

Image result for electromagnetic spectrum

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Electromagnetic spectrum: Inverse Square Law

Waves transfer energy, and energy is a quantity that is always conserved. Wave-fronts propaganding out from a point or a sperical source will themselves be spherical. As each wave-front increases in radius it also increases in area.  The formula for the surface area of a sphere of radius r is 4(pi)r2. The energy in the moving wave-front is distributed over that expanding area, and so its intensity decreases accordingly: 

I = k / r2

where I is intensity of wave, k is a constant and r is distance from source.

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Critical Angle

Sin C= 1/N

Ligth bends meaning that in the medium the light has slowed down. When it comes back out it speeds up again. 

Image result for critical angle

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Diffraction Grating

Diffraction os a key characteristic of all waves. It means the tendency of a wave to spread out in all directions, transferrring energy to its surroundings as it does so.

A diffraction grating is a flat plane object. It has a series of regular lines formed on it that block parts of an advancing wave-front. 

Superposition- is the adding together of wave displacements that occurs when waves from two or more seperate sources overlap at any given location in space. Displacements simply add.

Path difference- is the difference in length between two (straight lines) rays, e.g. one from a particular grating gap to a given pint in space and the ray from the next-foor grating gap to the same point.

Interference pattern- a stationary pattern that can result from the superposition of waves travelling in different directions, provided they are coherent. 

Coherent- literally means 'sticking together' and is used to describe waves whose superposition gives a visible interference pattern. To be coherent, waves must share the same frequency and same wavelength abd have a constant phase difference.

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Diffracting gradient

  • If the advancing wave-front encounter a flat obstacle in front of them, like a wall, most of the waves's energy is either absorbed or reflected by the wall. 
  • If the obstacle has edges or gaps, wave energy can travel round the edges or through the gaps. It is then that you may notice diffraction occurring.
  • Although after going through a gap much of the wave energy does keep moving forwards, some of it spreads out in other directions.
  • When a wave-front meets a diffraction grating, some of the wave's energy continues propagating forward through the gaps between the grating lines. This is transmission.
  • Some more of the wave's energy may be absorbed in the grating itself, but the remainder of the energy is scattered backwards as a reflection.
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Diffracting gradient

Gratings in Reflection mode:

  • In reflection mode, instead of looking at what comes through a grating, you look at the part of the wave energy that is bounced back off the grating surface.
  • Once again, because the grating lines are regularly spaced, an interference pattern is produced.

Image result for diffraction grating

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Diffracting gradient

Coherent Light Sources:

  • When light is emitted from or absorbed by matter, you can only explain what happens by thinking of light as being composed as tiny particles or 'packets of energy', which are called photons.
  • When thinking about the coherence of light, you have to combine ideas from wave theory with the idea of individaul photon particles- what is called 'wave-particle duality'.
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Diffracting gradient

Emission Spectra:

The quantum theory of light and other electromagnetic radiations is based on the experimental observation that there is a simple relationship between the frequency, f, of the radiation and the energy, E, carried by each photon:

E=hf

where h is the Planck constant, -6.626070 x 10-34Js. That constant of proportionaly bewteen energy and frequency has been very precisely measured and experiments indicate is it universal.

If a chemical element or compound is vapourised by heating in a flame, or if you pass an electric current at high voltage through a gas, you typically see light emitted of a characteristic colour, according to the chemical nature of the material you are testing. When you look at the spectrum of that light, by splitting it up using a prism or diffraction grating, what you see is a number of bright, coloured lines at definite frequencies. This is an emission spectrum. Each line in the spectrum matches to photons all emitted with very nearly the same frequency - and therefore they also each have virtually the same energy. 

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Speed Of A Transverse Wave On A String

The lower the critical angle, the slower the light. 

v= √T/(kg/meters)

v= speed

T= string tension

M/L= mass per unit of length

Image result for mass per unit length equation (http://www.pstcc.edu/departments/natural_behavioral_sciences/Web%20Physics/E2120D0201.gif)

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Speed Of A Transverse Wave On A String

Wavespeed: m/s

Tension: N

Mass: Kg

Length: M

μ: Kgm-1

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Speed Of A Transverse Wave On A String

Example question: 

Calculate the speed of the wave on a string when the string is tensioned to 5.5N. The string mass is 1g and the length is 25cm. 

1/1000= 1 x 103

25/ 100= 0.25

v= √5.5/ (0.001/ 0.25)

v= √5.5/0.004

v= 37.08ms-1

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Reflective Index

Critical Angle: the angle of incidence beyond which rays of light passing through a denser medium to the surface of a less dense medium are no longer refracted but totally reflected. (deviant from the norm).

Refractive Index: the ratio of the velocity of light in a vacuum to its velocity in specified medium.

Constructive wave: occurs when waves come together so they are in phase with each other, they must have the smae frequency.

Destructive wave: 2 waves with the same amplitude are out of sinc by 1(pi) or 1/2 a wavelength and cancel each other.

Superposition: The combination of two or more physical states to form a new physical state.

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Refractive Index

n = C/V = sin / sin r

n= refractive index

c= constant (speed of light in a vacuum-- always 3 x 108)

v= speed of light in a medium ms-1

sin i= incidence angle

sin r= refracted angle

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Refractive Index

Example question:

The refractive index of a material is 1.33, if the velocity of light in a vacuum is 3 x 108ms-1, find the velocity of light in the material.

V= C/N

V=3 x 108 /1.33

V= 225563909.8 ms-1

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Diffraction Grating And Inverse Square Law

The laser from the scanner produces a steady, focus stream of light. This is an exampleof coherent light. Its photon, or particles of light energy, posses the same frequency and its waves are in phase with another.

Image result for red orange yellow green blue indigo violet waves

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Diffraction Grating and Inverse Law

The double slit experiment:

A coherent light is shot through two slits. These did not show us as two lines, but areas with light and areas without. This is because of the areas of constructive and destructive waves. When the light is shown through, it is diffracted and spreads out and around the area. Light through both of the slits mean that the waves coming  would interfere with each other, some constructive and some descructive, therefore causing the areas of light and no light. 

If you use white light, there will be many colour present, this is because white contains a lot of colours and wavelengths. Whereas if a blue light was used then it would only be blue light present. 

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Diffraction Grating and Inverse Law

I= K/r2

r= K/I

K= Ir2

  • I= intensity of the wave
  • K= constant (based on the source)
  • r= radius (distance from the source)
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Electromagnetic spectrum

Ultraviolet:

  • Frequency: 7.5 x 1014 – 3 x 1016
  • Wavelength: 400nm – 10nm

X-Rays:

  • Frequency: 3 x 1016 
  • Wavelength: 10nm

Gamma Rays:

  • Frequency: >1020
  • Wavelength: <10-12 pm
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Communication

Satellite: microwaves- long distance communication.

Moblie phones: microwaves- talking to people.

Bluetooth: radiowaves- speakers & headphones.

WiFi: radiowaves- sends communications.

Infrared: infrared- short distance communications.

Optical Fibres: visable lights- broadband & landlines (travels at the speed of light so is too fast to be hacked).

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Communication

Optical Fibres: 

Optical fibres made from high-density glass can carry light signals long distances without losing any light through their sides.

Criticle angle:

The critical angle, C, is the least angle of incidence at which total internal reflection occurs.

  • Only applies when light tries to leave an optically dense (that is, high refractive index, n) medium at a boundary into a less dense (lower rafractive index) medium. 
  • As angle of incidence increases, angle of refraction also increase and is always larger.
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Fibre Optic

Light  (or electromagnetic radiation or other frequencies) travels best through a vacuum. Its rapidly oscillating electric field generates an oscillating magnetic field, and the changing magnetic field in turn generates another nearby oscillating electric field. And so the wave progresses rapidly through space.

Refractive index= n = C/V

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Fibre Optic

  • When the waves have to travel through matter, their progress is impeded by the electronic charges in the atoms and molecules. Metals, which are full of freely moving electrons, just stop the wave oscillation completely.
  • Many other materials absorb some or all of the light and so look coloured or even black 
  • In transparent materials, like water, glass and many plastics, the waves are not stopped or absorbed, but they are slowed down. The ratop of the speed of light in vacuum, c, to its speed in the material medium, v, is called the refractive index, n, of the medium.
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Fibre Optic

Image result for refractive index

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Fibre Optic

Critical Angle: When light passes from one medium (material) to another it changes speed. This is because the speed of a wave is determined by the medium through which it is passing.

When light speeds ups as it passes from one material to another, the angle of refraction is bigger than the angle of incidence. For example, this happens when light passes from water to air or from glass to water. 

When the angle of refraction is equal to 90 degrees, the angle of incidence is called the critical angle. At any angle of incidence greater than the critical angle, the ligth cannot pass through the surface - it is all reflected.

This is called total internal reflection.

Total because all of the energy is reflected. Internal because the energy stays inside the material. Reflection because light is reflected.

The relationship between critical angle and refractive index is sin (degrees) = 1/N.

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Optical Fibres

Optical fibres are very long thin cylinders of glass or, sometimes, plastic. Light is fed into the cut end of the fibre, so when it hits the sides of the fibre, it almost always does at angles greater than the critical angle. That meqans all the rays of light get totally interanlly reflected and keep bouncing down the length of the fibre.

  • No wave energy gets lost through the walls of the fibre, although as glass is not perfectly transparent, some is gradually absorbed.
  • This makes light in optical fibres a much more efficient way of transmitting signals than sending electrical pulses down copper cables. Copper cables suffer from quite large losses due to electrical resistance, meaning that after a few hundered metres most of the signal has been attenuated away and amplifiers are needed to boost it up again.
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Optical Fibres

Fibre Optics In Medicine:

  • Endoscopes are optical instruments with long tubes that can be inserted into a body organ through an opening such as the throat, nose, ear canals and anus.
  • These allow a trained medical pracctitioner to see inside a body organ, for example, the upper oesophagus and stomach or the colon and instestines, without undertaking surgery.
  • Endoscopes are also used during keyhole surgery to guide the use of surgical instuments with remote handling, whuch are often incorporated into the same tube system. 
  • Each fibre in the bundle is as thin as a human hair and consists of:
    • a core
    • cladding
    • protective plastic buffer coating
  • The image transmitted is pixalated(i.e. formed of coloured dots), since each fibre only transmits one pixel of coloured light. So the resolution of the image depends on the number of fibres in the bundle.
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Optical Fibres

Fibre Optic broadband networks

Broadband is used as a relative term to indicate the speed and carrying capacity of a data channel. In connection with the internet it has been used to market the improvement from earlier telephone dial up connections, which were very limited and slow. Fibre optic broadband has been prograssively replacing copper cable connections with consequent gains in data speed.

Multimode Fibre is the standard fibre cable used fro sending optical signals over short to merdium distances- for example, connections to instruments, jumpers in cabinets, small local area networks.

Single Mode Fibre has an even narrower core, which is less than ten wavelengths of the infra-red light that is used in them. This means there is just no space for different beams travelling at different angles down the core. Instead, the light wave moves as a single wave-front straigth down the centre of the fibre, and all the signal energy reaches the far end of the fibre at the same instan. Millions of kilometres of high quality cable is laid every year to build the fibre optic networks fro telephone, cable TV and broadband internet communications.

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Formulae Sheet

Wavespeed= frequency x wavelength

Speed of a transverse wave on a string= squareroot of (Tension/ (m/kg))

Refractive index= Constant/ Speed of light in a medium ms-1 = incidence angle/ reflected angle

Critical angle= sin C= 1/n

Inverse square law in relation to the intensity of a wave= I = k/r2

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