Physics 3.3 Demonstrate Understanding of Wave Systems PDF
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NCEA
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This document is an NCEA Physics past paper, covering wave systems. It includes details on wave properties, electromagnetic waves, sound waves, reflection, refraction, diffraction, interference, standing waves, resonance, harmonics, and the Doppler effect. It's targeted at secondary school or high school students studying Physics.
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No Brain Too Small PHYSICS Demonstrate understanding of wave systems Subject Reference Physics 3.3 Title Demonstrate understanding of wave systems Level 3 Credits 4 Assessm...
No Brain Too Small PHYSICS Demonstrate understanding of wave systems Subject Reference Physics 3.3 Title Demonstrate understanding of wave systems Level 3 Credits 4 Assessment External This achievement standard involves demonstrating understanding of wave systems. Achievement Achievement with Merit Achievement with Excellence Demonstrate Demonstrate in-depth Demonstrate comprehensive understanding of wave understanding of wave understanding of wave systems. systems. systems. Assessment will be limited to a selection of the following: Phenomena, concepts and principles of wave systems: Interference (quantitative) of electromagnetic and sound waves, including multi-slit interference and diffraction gratings; standing waves in strings and pipes; harmonics; resonance; beats; Doppler Effect (stationary observer for mechanical waves). Relationships: dx vw d sinθ = nλ nλ = f′=f L vw ± vs Note: fB = f1 − f2 was not given on the Achievement Standard or in the resource booklet but is still very useful to explain Beats. No Brain Too Small PHYSICS Wave Properties A wave is a regular vibration that carries energy. Waves that travel through material media are of two basic kinds: transverse waves and longitudinal waves. We can look at both kinds of waves using a slinky spring stretched out on a smooth floor. Keeping one end fixed and shaking the other end from side to side will produce a transverse wave. Keeping one end fixed and pushing the other end in and out will produce a longitudinal wave. The frequency (f) of a wave is the number of oscillations per unit time. The frequency of a wave is the same as the frequency of the source that produces the wave. The unit of frequency is the hertz. The period (T) of a wave is the time that it takes for one complete oscillation. The unit of period is the second. The period and frequency of a wave are linked by the following relationship, The speed (v) of a wave is the distance travelled per unit time by the wave. The unit of speed is the meter per second, ms-1. The speed, frequency and wavelength of a wave are linked by the following relationship, The energy carried by a wave depends on the amplitude of the wave. The bigger the amplitude the more energy the wave carries. No Brain Too Small PHYSICS Electromagnetic Waves Electromagnetic waves are transverse waves that travel at the speed of light in a vacuum. Electromagnetic waves travel at different speeds in different media. Radio Low frequency Remember Microwaves My Infrared Instructions Visible (ROYGBIV) Visible Ultra Violet Under X rays X ray Gamma rays High frequency Glasses Sound waves Sound waves are longitudinal waves consisting of a series of compressions and rarefactions. The vibrations of the loudspeaker set up a series of compressions and rarefactions in the air. The graph of air pressure as a function of distance from the speaker is a sine curve. Sound waves are longitudinal produced by vibrating objects which could be: a string which is plucked (guitar), bowed (violin) or hit (piano) a column of air in a wind instrument or organ pipe The amplitude of the sound is the maximum displacement of the air particles from their rest position. It is also the difference between the maximum air pressure in a sound wave and normal air pressure. The greater the amplitude of the sound wave, the louder the sound. Sound waves travel at different speeds in different media but a lot slower than electromagnetic waves. In air, sound travels at 331 ms-1 at a temperature of 0°C but the speed of sound changes with temperature. Sound travels faster in warm air than in cold air. The speed of sound in a medium depends on the density and compressibility of the medium so is different for different materials (much like light passing through different materials). No Brain Too Small PHYSICS Wave Behaviour Reflection, refraction, diffraction and interference are behaviours of all types of wave. Reflection occurs when a wave bounces from the surface of an obstacle. None of the properties of a wave are changed by reflection. The wavelength, frequency, period and speed are same before and after reflection. The only change is the direction in which the wave is travelling (and possibly a phase change causing it to invert). Refraction occurs when a wave moves from one material to another. The speed and wavelength are changed by refraction. The frequency of the wave stays the same. The direction in which the wave is travelling may or may not be changed by refraction. Diffraction occurs when a wave passes through around an object or through a gap (called a slit or an aperture). When a wave passes through a gap the diffraction effect is greatest when the width of the gap is about the same size as the wavelength of the wave. Smaller obstacles and smaller gaps lead to more diffraction or bending of waves than larger obstacles or gaps, when you are comparing waves with the same wavelength. There is more diffraction or bending of waves with larger wavelength than of waves with smaller wavelength. The same happens with sound waves. This is the reason that you hear the thumping bass sounds from your local boy racers’ car stereo without hearing the smaller-wavelength higher sounds of the melody. Diffraction of light using blue and red light: Diffraction is caused by interference between rays passing through a single slit. Notice that, unlike an interference pattern, the light bands in a diffraction pattern are of decreasing intensity and decreasing width as you look along from the center of the pattern. No Brain Too Small PHYSICS The diffraction of light is harder to detect than the diffraction of sound because of the very small wavelength of light. Diffraction of sound waves through doorways and window openings is easily observed, and we can hear around corners, but we cannot see around corners. Interference When waves run into each other, they usually don't reflect. Instead, they combine. If the amplitudes of two waves add up then the new wave has larger amplitude. This is called constructive interference. When two waves of the same wavelength and frequency occur in the same place, they will have an effect on each other. If two waves are in sync, (the crest from one wave coincides with the crest from the other), they add up: this is a constructive interference. If the waves had opposite amplitudes (one pointed up and the other pointed down), then the new wave has a smaller amplitude. This is called destructive interference. If two waves are half a wavelength out of sync (the crests from one wave coincides with the troughs from the other), they cancel out, and the resulting wave will be zero; this is a destructive interference. Constructive interference will make a sound louder while destructive interference will make a sound quieter. Two coherent sources of waves can produce an interference pattern. For coherence: The frequency of the sources is the same There is a constant phase relationship between the sources. Young’s Double-slit experiment For any kind of wave, an interference pattern can be produced in a 'double-slit' experiment. A wave detector may be moved across the interference pattern to find points of constructive and destructive interference. For visible light, a screen is used to show the interference pattern at the plane of the screen. No Brain Too Small PHYSICS When white light is incident on a grating the central maximum is white. Spectra are produced at the other order maxima with blue light closest to the central maxima and red furthest. With a suitable grating, several orders of spectra may be observed. The central maximum is also called the zero order maximum. If Monochromatic light (light of one frequency) is used then constructive interference occurs at points where a wave from S1 arrives in phase with a wave from S2. To model this effect mathematically, we begin with two slits separated at their mid-points by a distance d. The slits are very small compared to the wavelength of light. Two light rays, r1 and r2, originating from a single light source, pass through the slits and strike a screen at a distance L from the slits. A series of light and dark bands called fringes will be seen on the screen. If the distance d