9102020 Now you see it Now you dont

9/10/2020 Now you see it, Now you don’t (Edexcel) W Richards The Weald School

Some 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) 9/10/2020

Some definitions… Transverse waves are when the displacement is at right angles to the direction of the wave… Longitudinal waves are when the displacement is parallel to the direction of the wave… 9/10/2020

Electromagnetic Radiation 9/10/2020 E-M radiation is basically a movement of energy in the form of a wave. Some examples:

The Electromagnetic Spectrum 9/10/2020 Each type of radiation shown in the electromagnetic spectrum has a different wavelength and a different frequency: High frequency, _____ wavelength Gamma rays X-rays Low frequency, _____ (high) wavelength Ultra violet Visible light Infra red Microwaves Radio/TV γ Each of these types travels at the same speed through a _______ (300, 000 m/s), and different wavelengths are absorbed by different surfaces (e. g. infra red is absorbed very well by ______ surfaces). This absorption may heat the material up (like infra red and _______) or cause an alternating current (like in a __ _______). Words – black, microwaves, long, short, TV aerial, vacuum

The Electromagnetic Spectrum 9/10/2020 Type of radiation Uses Dangers Gamma rays Treating cancer, sterilisation Cell mutation X rays Medical Cell mutation UVA, UVB and UVC Sun beds Skin cancer Visible light Seeing things None (unless you look at the sun) Infra red Remote controls, heat transfer Sunburn Microwaves Satellites, phones Very few TV/radio Communications Very few

Mobile Phones Advantages 9/10/2020 Disadvantages

Detecting things by absorption 9/10/2020 X-Rays – x-rays are absorbed by ______ material (e. g. bone) and pass through softer material. Satellites use ______ to measure areas of probable high rainfall as microwaves are absorbed by _____. When paper is exposed to UV some light is absorbed and them emitted as ______ light. UV can be used to detect if a banknote has been made from the wrong ink (i. e. a _____). Words – forgery, denser, water, visible, microwaves

9/10/2020 Detecting things by emission – infra red

9/10/2020 Detecting things by emission – infra red

Detecting things by reflection - ultrasound 9/10/2020 Ultrasound is the region of sound above 20, 000 Hz – it can’t be heard by humans. It can be used in pre-natal scanning: How does it work? Ultrasonic waves are partly _____ at the boundary as they pass from one _______ to another. The time taken for these reflections can be used to measure the _______ of the reflecting surface and this information is used to build up a _____ of the object. Words – depth, reflected, picture, medium

Analogue vs. Digital Signals 9/10/2020 Analogue signals (like talking or music) continually vary in amplitude and/or frequency 1 0 + Digital signals, however, are either off or on, and the information is sent in a series of pulses (“binary”) There are two main advantages of digital: 1) More information can be sent down the same cable 2) Better quality, because a digital signal can be amplified without amplifying the extra noise:

Digital technology and music 9/10/2020 Digital technology means: 1) Keyboards can be attached to computers 2) CDs and DVDs have replaced tapes 3) MP 3 s 4) Synthesisers 5) Digital radio (DAB)

Refraction through a glass block: 9/10/2020 Wave slows down and bends towards the normal due to entering a more dense medium Wave slows down but is not bent, due to entering along the normal Wave speeds up and bends away from the normal due to entering a less dense medium

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Refraction 9/10/2020 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

Finding the Critical Angle… 9/10/2020 1) Ray gets refracted 3) Ray still gets refracted (just!) THE CRITICAL ANGLE 2) Ray still gets refracted 4) Ray gets internally reflected

Critical Angle and density 9/10/2020 Material Critical angle/O Density/kg/m 3 Ice 50 920 Water 49 1000 Perspex 42 1190 Diamond 24 3300

Uses of Total Internal Reflection 9/10/2020 Optical fibres: An optical fibre is a long, thin, _______ rod made of glass or plastic. Light is _______ reflected from one end to the other, making it possible to send ____ chunks of information Optical fibres can be used for _____ by sending electrical signals through the cable. The main advantage of this is a reduced ______ loss. They also suffer less interference and can’t be “tapped”. Words – communications, internally, large, transparent, signal

The Wave Equation 9/10/2020 All E-M waves obey the Wave Equation: Wave speed (v) = frequency (f) x wavelength ( ) in m/s in Hz in m V f

Some example wave equation questions 9/10/2020 1) A water wave has a frequency of 2 Hz and a wavelength of 0. 3 m. How fast is it moving? 0. 6 m/s 2) A water wave travels through a pond with a speed of 1 m/s and a frequency of 5 Hz. What is the wavelength of the waves? 0. 2 m 3) The speed of sound is 330 m/s (in air). When Dave hears this sound his ear vibrates 660 times a second. What was the wavelength of the sound? 0. 5 m 4) Purple light has a wavelength of around 6 x 10 -7 m and a frequency of 5 x 1014 Hz. What is the speed of purple light? 3 x 108 m/s

The Structure of the Earth 9/10/2020 A thin crust 10 -100 km thick A mantle – has the properties of a solid but it can also flow A core – made of molten nickel and iron. Outer part is liquid and inner part is solid How do we know this? These facts have all been discovered by examining seismic waves (earthquakes)

Seismic waves Earthquakes travel as waves through the Earth – we call them SEISMIC WAVES. There are two types: P waves: 1) They are longitudinal so they cause the ground to move up and down 2) They can pass through solids and liquids 3) They go faster through more dense material S waves: 1) They are transverse so they cause the ground to move from right to left 2) They ONLY pass through solids 3) They are slower than P waves 4) They go faster through more dense material 9/10/2020

Seismic waves 9/10/2020 S waves will only travel through a solid P waves travel through the Earth and are refracted when they pass through a medium The paths of these waves are all curved because density is gradually changing These observations tell us 3 things about the Earth: 1) It has a thin crust, 2) it has a semi-fluid mantle where density increases with depth, 3) a core with a liquid outer part and a solid inner part.