Alternative transcript:

difference in the distance from the sources to the point where they meet. If two paths are different they can cancel or add depending what the difference is. Reinforcement Cancellation Constructive Interference Destructive Interference Constructive interference - Adding together, this path difference between the waves is a whole number of wavelengths so the waves arrive in phase, adding together to give a larger wave. Destructive interference cancelling out the path difference between the waves are half the wavelengths so the waves arrive out of phase, cancelling out to give no wave at all. Diffraction Diffraction is the effect produced when waves bend around an obstruction and pass into the region behind the object. Physics The amount of diffraction depends on the size of the objects and the wavelength of the wave. Wide Gap Wave Diffraction Narrow Gap When a wave passes through a gap they spread out (diffraction). In the wide gap, the wavelength is several times wider than the wavelength, however the narrow gap is closer to the wavelength therefore diffraction is greater. There is no change in wavelength that passes through the gap. Phase difference Phase difference is to do with the position of a point in a sine wave oscillation. Related to other points in the wave or in another wave. Current A Φ waves. All points oscillating in a wave occur at the same frequency but they have different amplitudes at the same time. Concept of Phase π/2 +Vm +im 0 T Electronics Coach Two waves can be out of phase as their points are oscillating at the same frequency but the displacement of the points is different in the two Phase Difference M 2m Time (seconds) Waves can be 90 out of phase or 180° out of phase. Voltage. (V) -İm -Vm 360 = 2πr 180 = 7 اليا Current, (1) T 2π 8 = ot Stationary and progressive Ć = Physics Antinode The wave pattern is also called fundamental and condition will be: Crest * Y L (distance between the nodes) 1/2 2, If the speed of a wave described before then the fundamental frequency will be. (Fo v/ 2 V/2L. Progressive waves propagate through a substance. Disp waves Speed- tension x (mass of string/length of string) When working out tension or mule Node Trough Standing stationary waves are produced when progressive waves of the same frequency and amplitude pass through another in opposing directions. Speed of a transverse - a string. wave on a T Time U Emission spectra An emission spectra is the range of frequencies of the light emitted by an element. The emission spectra is produced by an element due to energy. level changes of the electrons, as the electrons lose energy when returning to a lower level they emit a specific frequency Emission and absorption spectra: (a) Emission Spectra P Hot gas (b) Absorption Spectra High density Cold gas hot matter Emission spectrum Absorption spectrum Emission Line line spectra: -bright lines at certain wavelengths. - hot gas produces light collisions causing excitation of atoms. gas Absorption line spectrum - dark lines at certain wavelengths in a continuous spectrum - light passes through a cool. gas. Identifying gases The emission spectra of each element is unique and so can be used to identify the element. Elements such as mercury, sodium, lithium, potassium and other heavy metals can be vaporised to form gases that can be energised to emit. Diffraction grating A diffraction grating is a series of narrow, parallel slits. They usually have around 500 slits per mm. When the light shines on the different grating serval bright sharp lines can be seen, The first bright line lies directly behind where the light shines. PARALLEL BEAM OF MONOCHROMATIC LIGHT OR LASER LIGHT The DIFFRACTION GRATING zero Physics order maximum (n=0): There is no path difference between SCREEN The first order maximum (n=1) neighbouring waves. They arrive in phase and interfere constructively. There is a path difference of I wavelength between neighbouring waves, they arrive at phases and interfere constructively. The second order maximum (n=2) There is a path difference of 2 wavelengths between neighbouring waves, they arrive in phase and interfere constructively. Between the maxima: The path difference is not a whole number of wavelengths so the waves arrive out of phases and interfere destructively. Absolute refractive index: N = Refraction The absolute refractive index of a material is a measure of how easy it is for light to travel through it, the refractive index of material can be calculated using. C/N = sin i sin r Refraction index = speed of light in air/ speed of light in material. Speed of light = 3x10 (power of 8) Celative refractive index N-C -sin i V sin r Incident Ray 0₁ Normal 10, Refracted Ray Whenever two materials touch the boundary between them they will have a refractive index dependent on the refractive indices of two materials. When light travels from one material to material 2 the relative refractive index can be calculated (in2= n2/ni= sineal / sine02) Jotal internal reflection When does total internal refraction occur? when the angle of incidence in glass is Physics greater than the critical angle When light travels from a dense medium to a less dense medium (from glass to air) Light ray When the angle of incidence is greater than the critical angle, the ray has been totally internally reflected. Total internal reflection glass Glass Applications of total internal reflection (TIR) Total internal reflection allows light to be contained and guided along very thin fibres. usually made from glass these are optical fibres which have many functions, → fibre broadband internet sends computer information coded as pulses of light along underground optical fibres, → doctors can look at the inside their patients using an endoscope - a long tube which guides light into the patient and then guides the reflected light back out to give an image. → decorations, like some artificial Christmas trees, carry coloured light to different parts of the decoration and let it shine out in different directions. Critical angle The critical angle, is the least angle where total internal refraction occurs, → Only applies when light tries to leave an optically dense medium at a boundary into a less dense medium, → As the angle of incidence increases the angle of refraction also increases and is always larger, some light is always internally reflected → For incidence at the critical angle, the refracted beam would be at 90 degrees, that is along the boundary surface therefore it disappears and is instead total internal reflection, Physics Optical fibres Optical fibres are used to transmit light or signals, they can also be used for communication in medicinal applications, • They rely on critical angles and total internal reflection to function. • Fibre optics work by light being guided through the core therefore the fibre acts as an optical waveguide due to the angle of incidence aways being equal to the angle of reflection. The reflected light continues to be reflected, the light ray that continues to bounce down the length of fibre optic cable, Optical fibres against copper wires: → Optical fibres have lower losses, therefore travel further before needing amplification, Secure, they can not be tapped into, → They carry higher frequencies, so provide greater bandwidth However optical fibres cost more and need specialist installation, Endoscopy Forming an image: Lenses are used at both ends, • A tiny objective lens at the digital end of an endoscope focuses an image onto cut ends of the optical fibre, • Each fibre in the main bundle collects and carries the light for one pixel. • An eyepiece lens at the operator end takes light existing the fibre bundle and refocuses it to be viewed as an image directly by eye or with camera, Analogue images: Optical fibres maybe divided into pixels, these images are analogue, the brightness and colour of each pixel vary with time in direct proportion to the light collected by the objective lens, Other devices using critical angle and total internal reflection: • Fingerprinting for security, where fingerprint lines touch the glass they alter the critical angle and give a certain amount of light reflected back internally to a detector, ● Rain detectors on car windscreens water on glass windscreen is politically denser than air therefore it alter the critical angle, Musical instruments Strings: Physics Stringed instruments use transverse waves The fixed ends are always nodes The fundamental modes one antinode so L=N2₁ For higher harmonics, any number n of antinodes can fit in the length of the strings therefore L-N₂n Tubes and pipes: Tubes and pipes are longitudinal sound waves, to create a resonator, open ends of the pipe are antinodes. therefore a pipe open at both ends are, X= 1/₂2n Closing one end of a pipe creates a node Calculation of critical angles at a glass air interface Sin c = .!. Analogue and digital signals Analogue signals are continuous signals, analog signal www.m digital signal Digital signals are either on or off, Advantages ● Can carry more information in the same time as they can be multiplexed. • Noise can be removed or less interference and so improved signal reception quality, Signal can be regenerated so the wave can travel Signal can be encrypted to improve security Analogue to digital conversion: An analogue to digital converter samples data of the voltages of the analogue signal at a set time interval, the sampled voltage are converted to a binary code which are the transmitted as a digital signal Electromagnetic waves The inverse square law: Waves that radiate in all directions from an antenna have spherical wave fronts therefore loose intensity. K Physics 2 I XR² Electromagnetic, wave in Communication Satellite communications: High power signals over very long distances concentrated by dish antenna. Frequency band is 1-40 ghz (microwaves) Receive incoming upload signals, amplify them and retransmit them as a download signal on a different frequency band Mobile phones High powered network which ranges serval km, Frequency band is 8000mhz- 2.6ghz (uhf radio waves to microwaves) Allocates to different operators (29,3g) which offers increasing speeds for data, higher frequencies have higher data capacity but travel less distance and penetrate from air to a building. Bluetooth and wifi : Low power device ranges to lom, -10-100m Bluetooth and wifi would interfere because they used the same channel for a extended period however modern bluetooth uses frequency hopping so bluetooth and wifi can maintain as much data, Infrared: Ir wavelength 870 nm or 930-950 wavelength and frequency is 320thz used for tv remotes controls and for data transfer between computers, phones however does not work in direct sunlight, 10 Memorising the wavelength or frequency then you can use the wavelength equation to calculate the other electromagnetic waves. 1 FREQUENCY AM radio waves WAVELENGTH Short-large 10 101 10 12 bluetooth 2.4-2.4835ghz boardline microwaves and radio waves, wifi ranges 10 10 Low power device (only ranges a couple of metres) 15 10 21 Frequency regions of the electromagnetic spectrum VHF (FM) UHF (TV) Microwaves Infrared rays Visible liht ultraviolet x-rays Gamma rays 10 10 -2 10-3 10 4 -12 10 www 480 TH 510 TH 560