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T1Wk10 Wave Properties

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Information about T1Wk10 Wave Properties
Education

Published on February 14, 2008

Author: Ubert

Source: authorstream.com

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Lesson 1:  Lesson 1 Lesson Objectives Understand the terms ‘wave’ and ‘wave motion’ Wave Activity (1):  Wave Activity (1) The Kallang Wave What have you noticed about the wave or the individual? They are moving up and down They remain at the same position The wave started from the side The wave is moving from left (start) to right (end) What have we gathered…:  What have we gathered… A wave is created… By a vibration or oscillation A wave is the… Spreading of disturbance from one point to another Wave Activity (2):  Wave Activity (2) Using a rope… If we start the wave using the right hand (as shown), describe what you feel on your left hand? What have we gathered…:  What have we gathered… Do you feel this is on left hand? A force from the rope, trying to move the left hand up and down together the wave… How can we explain this? The wave motion is a mechanism for the transfer of energy from one point to another (Without the transfer of the medium) Wave Motion:  Wave Motion Let us analyze the rope again… Below are snapshots taken (in ‘running’ order) It shows the vertical displacement caused by the wave, along the rope The dots represent particles on the rope Try answering these… Which direction is the wave propagating (moving)? Taking the bigger dot as reference, can you plot it’s vertical displacement against time? Wave Motion:  Wave Motion Is this what you found? The wave is moving from left to right. The displacement vs time graph of the particle looks something like this… Questions?:  Questions? Self Check From the waveform, can I Identify the wave motion and direction? Lesson 2:  Lesson 2 Lesson Objectives Identifying the transverse wave Its Properties Is it really called ‘Kallang Wave’?:  Is it really called ‘Kallang Wave’? It is known as a transverse wave… It is a wave where the direction of travel is PERPENDICULAR to the direction of vibration. Transverse Waves:  Transverse Waves A transverse wave has got peaks and valleys at regular intervals. The peaks are called the ‘crest’ The valleys are called the ‘trough’ Is that all?:  Is that all? Apart from understanding the wave, the wave motion, we must also be able to read, analyze and even draw the waveform. We are also required to understand and interpret the following terms used. Eg: Amplitude Phase Wavelength Frequency Period Wave Speed NO! To Describe A Wave:  To Describe A Wave Amplitude of a transverse wave Maximum displacement from the rest position ½ the vertical distance between the crest and trough SI Unit (m) A A A A To Describe A Wave:  To Describe A Wave Two points on the wave are said to be in phase if They are moving in the same direction Have the same displacement from the rest position Eg. The points p, p’ and p” are in phase. To Describe A Wave:  To Describe A Wave Wavelength, Distance between 2 successive crests or troughs Shortest distance between any 2 points that are in phase SI Unit (m) To Describe A Wave:  To Describe A Wave Frequency, f Number of complete oscillations per unit time SI Unit (s-1) or Hz Period, T Time taken to produce a complete oscillation SI Unit (s) Relationship To Describe A Wave:  To Describe A Wave With the wavelength and frequency of a wave, we know how many waves and how far the series of waves will cover per unit time. This is known as wave speed – distance traveled by a wave per unit time. Recall speed = So for waves, speed v = distance covered in 1 wavelength time taken to cover 1 wavelength Recall f so speed of waves v = Speed equation for waves v = f (Unit : ms-1) Example:  Example Q. A fisherman notices that wave crests pass the bow of his anchored boat every 3.0s. He measures the distance between two successive crests to be 6.5m. How fast are the waves travelling? A. From the question, we know the period, T = 3.0s, and the wavelength is 6.5m. Therefore, wave speed, v = 6.5 / 3 = 2.2ms-1 (1 dp) Transverse Waves:  Transverse Waves Examples of transverse waves Water Waves Electromagnetic Waves Questions?:  Questions? Self Check What are the properties I learnt? What do each property tell me about the wave? How many properties do I need to draw a waveform? How many properties can I identify given the waveform? Name some transverse waves. Lesson 3:  Lesson 3 Lesson Objectives The phenomenon called ‘wavefront’ Introduction to Longitudinal Wave Lunch Time Prelude…:  Lunch Time Prelude… Using a pail or basin with a large surface area… Try tapping your finger on the calm water surface What do you notice? Do you see ‘circular’ waves being formed? What is this imaginary ‘circular’ line we see? Interesting Phenomenom:  Interesting Phenomenom That is a… wavefront - an imaginery line on a wave that joins all points which have the same phase of vibration. The other type of wave called…:  The other type of wave called… … Longitudinal Wave… What is a longitudinal wave? A wave where the direction of travel is parallel to the direction of vibration. How does it look like?:  How does it look like? Demonstration of a longitudinal wave? Slinky Coil On an Applet Longitudinal Waves:  Compression Places where air pressure is slightly higher than the surrounding air pressure. Rarefaction Places where air pressure is slightly lower than the surrounding air pressure. Longitudinal Waves Longitudinal Waves:  Longitudinal Waves Examples - Sound waves Longitudinal Waves:  Longitudinal Waves In your pairs now… How would you determine the wavelength, period, and frequency of a longitudinal wave? Is there an amplitude in this case? Example:  Example Q. A sound wave in air has a frequency of 262Hz and travels with a speed of 343m/s. How far apart are the wave compressions? A. Given f = 262 Hz and v = 343m/s, Distance between wave compression = wavelength = v / f = 1.3m (1 dp) Questions?:  Questions? Self Check What is a longitudinal wave? How do we determine the different properties of this wave? Can you list down some of the similarities and differences between the 2 types of waves? Lesson 4:  Lesson 4 Lesson Objectives Summarize what we have learnt so far To differentiate between a transverse and longitudinal wave To explain the stroboscope demonstration in terms of frequency and phase What we discussed so far?:  What we discussed so far? Rarefactions Compressions Troughs Crests General Wave Properties Types of Waves Wave Terms Transverse Longitudinal Frequency Period Speed f = 1/T Speed, v = fl Examples Transverse Vs Longitudinal Waves:  Transverse Vs Longitudinal Waves Similarities Created by a source of vibration or oscillation The spreading of disturbance from one point to another Differences Different direction of travel Stroboscope and its Frequency (Optional):  Stroboscope and its Frequency (Optional) In our demonstration, we shone the stroboscope on the ceiling fan, and noticed 3 different situations. In the 1st case, with a suitable frequency on the stroboscope, the fan blade appears to be stationary. In the 2nd case, by lowering the frequency of the stroboscope, the fan now appears to be turning anticlockwise (forward). Lastly, by increasing the frequency of the stroboscope, the fan blade appears to be turning clockwise (backwards). What actually happened? Case 1: Stationary:  Case 1: Stationary Let us label the blades I, II and III respectively. The blade appear stationary as the stroboscope flashes at an interval whereby the fan rotates 120o. In the diagrams below, it shows the 3 possible position when we saw the fan as stationary. I II III II III I III I II Case 1: Fan appears faster:  Case 1: Fan appears faster In this case, the stroboscope flashes at an interval slower then the rotating fan Hence instead of capturing the image of the fan as stationary, the image appears to be moving forward. Note the angle each blade has rotated… I II III II III I I II III Case 3: Fan appears slower :  Case 3: Fan appears slower In this case, the stroboscope flashes at an interval faster then the rotating fan Hence instead of capturing the image of the fan as stationary, the image appears to be moving backwards. Note the angle each blade has rotated… I II III I II III I II III What does it mean?:  What does it mean? When 2 points are in phase, they appear to be in ‘sync’ (do not use this in test or exams) Similarly, the idea is like soldiers marching. Questions?:  Questions? Self Check Make a comparison between the transverse and longitudinal wave? What can you infer from the stroboscope regarding the term ‘phase’? Lesson 5:  Lesson 5 Lesson Objectives To observe the production of different waves pattern Understand what happens when the speed of a wave reduces To see and understand what happens when waves are reflected To see and understand what happens when waves are refracted Wave production:  Wave production In this lesson, we shall make use of plane waves for our demonstration… Recall… A circular dipper produces So a straight dipper produces Wave Production:  Wave Production In addition, a possible setup we can use… A Ripple Tank What happens when…:  What happens when… Waves goes from deep water to shallow water? Frequency remains unchanged as it is determined by the source What about the wave speed? And the wavelength? What do you think will happen if waves goes from shallow to deep water then? Shallow Water What happens when…:  What happens when… A straight barrier is placed at an angle along the incoming waves? The incoming water waves is reflected. What happens when…:  What happens when… A piece of glass block is submerged at an angle to the incoming water waves? As water enters a shallow region, the speed and wavelength reduces. Since the wave enters at an angle, the resultant wave appears refracted. Questions?:  Questions? Self Check Can you explain the ‘piling-up’ effect, as in how the tsunami rose to such great heights? Did the wavelength change during reflection or refraction of water waves? Lesson 6:  Lesson 6 Lesson Objectives Introduction to Electromagnetic Waves for Peer Teaching Electromagnetic Waves:  All these waves Radio Waves Microwaves Infra-red Visible Light Ultra-violet X-rays Gamma Rays …are part of the EM Spectrum. Electromagnetic Waves Electromagnetic Waves:  But how are the waves ordered? Electromagnetic Waves Increasing Wavelength Increasing Frequency Increasing Energy Electromagnetic Waves:  Electromagnetic Waves What do EM waves have in common? They are all transverse waves. They all travel at a speed of 3 x 108 ms-1 in vacuo. They are all electromagnetic radiation, which can be used to transfer energy. Do not need a medium to propagate. They obey the laws of reflection and refraction. They can be emitted and absorbed by matter. Their frequencies do not change when they enter from one medium to another. The wave equation v=fl is applicable to all these waves. * They carry no charge. EM Waves in Action:  EM Waves in Action

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