Transverse Waves and Pulses Teacher Guide Series Overview
There are six lessons in this series in which we investigate transverse pulses and waves moving through a spring or string. During these lessons we identify characteristics of both transverse pulse and transverse waves, explain and analyse wave motion and explore the wave properties of refraction, reflection and interference.
Curriculum Links
This series of lessons links to the core knowledge area of Waves, Sound and Light. We have chosen to address the themes transverse pulses on a string or spring and transverse waves. We have shown that waves can be found in many different contexts but have focused on pulses and waves moving through a slinky spring. In this series we have addressed Assessment Standards related to: • Learning Outcome 1: Scientific Inquiry and Problem-solving Skills • Learning Outcome 2: Constructing and Applying Scientific Knowledge
E Educational Approach
We have chosen to investigate both transverse pulses and transverse waves in this series because they are so closely related. We start by investigating pulses and then apply what we have discovered to waves. In this series we have aimed to show clear demonstrations of both transverse pulses and transverse waves. We have used special slow motion sequences of these demonstrations to analyse the characteristics, motion and properties of pulses and waves. The analysis of real images helps to develop the important concepts through inquiry. This series is also linked to the theme of motion. We apply the skills of graphing to analyse the graphs of wave motion. In these graphs we have analysed both the motion of the particle and the motion of the pulse or wave moving through the medium. As you watch each lesson, make a note of materials and other resources you might need to bring to the class. For example, you may need slinkies of different densities to demonstrate refraction.
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Physical Sciences Grade 10
Teacher Guide
Transverse Waves and Pulses Teacher Guide Series at a Glance Lesson Title
Lesson Outcomes
Lesson 1 An Introduction to Pulses and Waves
• Describe what a transverse pulse is • Explain the relationship between transverse pulses and transverse waves
Lesson 2 Wave Motion
• Describe the motion of a pulse through a medium • Explain the relationship between wave speed and frequency • Calculate the speed of a transverse wave
Lesson 3 Graphing Wave Motion
• Describe the motion of particles in a transverse wave • Draw motion graphs to represent the motion of a single particle
Lesson 4 Properties of Transverse Pulses
• Describe and explain the refraction of a transverse pulse at a boundary • Describe and explain the reflection of a transverse pulse at different boundaries
Lesson 5 Superposition
• Predict and explain what happens when two pulses meet by applying the principle of superposition
Lesson 6 Standing Waves
• Explain how standing waves form • Describe the relationship between a standing wave pattern and the boundaries of the wave
By the end of this lesson, the learner should be able to:
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Physical Sciences Grade 10
Teacher Guide
Transverse Waves and Pulses Teacher Guide G
Teaching Guidelines
Lesson 1: An Introduction to Pulses and Waves
In this lesson we begin by looking at different waves in every day contexts. We show a pulse moving through a slinky spring and use these images to build a definition of the term ‘pulse’. We have inserted a pause so that your learners can use their observations to build their own definition and then compare it to ours. We use this same method to build a definition of a wave. The crucial point of this lesson, which is carried through the whole series, is that there are two different types of motion taking place in a pulse or wave – the motion of the particles and the motion of the disturbance through the medium. We show these two different motions by attaching a ball to a spring and by using animations of pulses and waves. We also define the terms amplitude, pulse length and wavelength in this lesson.
Task assesses LO 2 AS 1 and LO 2 AS 2
Learners need to recall what is meant by the terms transverse wave, transverse pulse, amplitude and wavelength. We suggest that you get learners to draw their diagrams accurately, using a scale of 1cm: 1cm. They may find it easier to draw on squared paper or on graph paper.
Lesson 2: Wave Motion
The focus of Lesson 2 is on investigating relationships between wavelength, period, frequency and velocity of the wave. Your learners will have the opportunity to use these relationships to solve problems during the lesson and in the task given at the end of the lesson.
Task assesses LO 1 AS 3; LO 2 AS 1 and LO 2 AS 2
For this task learners need to do simple calculations using the wave equation. They will need to practise similar types of problems for homework. We suggest that you give learners a short class test (15 minutes) before watching the next video lesson, to ensure that learners have a clear grasp of all the terminology and the relationships that exist between these terms.
Lesson 3: Graphing Wave Motion
In preparation for this lesson we suggest that you revise the concepts of motion graphs. Learners need to recall that the gradient of the position versus time graph at a certain time gives the velocity at that time and that the gradient of the velocity versus time graph at a certain time gives the acceleration at that time. These concepts will be used when graphing the motion of a single particle of a medium which has been disturbed by a transverse wave and the motion of the disturbance as it moves through the medium. We start by examining the motion of a particle in the medium. This is possibly the most difficult concept in this series for Grade 10 learners to grasp. We suggest that you pause the video often and take time to make sure learners are on track and understand the concept. To actually monitor the motion of a single particle is difficult. Instead we show that the motion of a pendulum bob is exactly the same as the motion of a particle in a medium that has been disturbed by a transverse pulse or wave. We then use a motion sensor to collect data about the position of the bob during a certain time interval and from this data a position versus time graph is displayed on a laptop screen. Learners need to be given graph paper to sketch this graph for themselves. This will help them follow the analysis of the graph shown on the video. They will then be able to sketch a velocity versus time graph of the particle below the first graph. We have inserted a pause at this point and suggest that you get your learners to draw the acceleration versus time graph by themselves. They can then check their answers with those shown in the video.
Task assesses LO 1 AS 2; LO 1 AS 3 and LO 1 AS 4
Even if the learners have found it difficult to plot the motion of the particle they should find this task much easier. The wave moves through the medium at a constant velocity and so the acceleration is also constant but equal to 0m.s-2. Learners need to apply this knowledge when drawing both the velocity versus time and the acceleration versus time graphs.
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Physical Sciences Grade 10
Teacher Guide
Transverse Waves and Pulses Teacher Guide Lesson 4: Properties of Transverse Pulses
In Lesson 4 we focus on the behaviour of pulses at a boundary. We start by investigating what happens when two different springs are joined together. We observe refraction and then use the Law of Conservation of Energy to explain why the velocity of the wave changes when the medium changes. This will give your learners the chance to revise concepts they have learnt in the theme of gravity and mechanical energy. We also investigate the reflection of a pulse from a fixed end and from a free end. The use of slow motion video sequences and animation will help your learners analyse what happens in each of these situations.
Task assesses LO 1 AS 2; LO 1 AS 3 and LO 2 AS 2
Learners need to interpret velocity versus time graphs in order to identify where reflection and refraction are taking place.
Lesson 5: Superposition
In this lesson we investigate what happens when two half pulses meet in the same part of the medium. This lesson clearly shows both destructive and constructive interference. We use this evidence to introduce the principle of superposition. Although this statement is quite long we break it down and apply it to an example.
Task assesses LO 1 AS 2; LO 1 AS 3; LO 2 AS 1 and LO 2 AS 3
The task in this lesson will give learners the chance to apply the principle of superposition to a simple example. Learners need to draw diagrams to identify types of interference.
Lesson 6: Standing Waves
In the final lesson of the series we show what happens when two waves interfere in a rubber chord that has a fixed end and a free end. We examine the standing wave pattern and show how it changes as the frequency of the vibrator changes. It is important to note that the frequencies are quantised.
Task assesses LO 2 AS 1; LO 2 AS 2 and LO 2 AS 3
Learners need to explain why an anti-node forms at the free end of a standing wave. They need to recall that reflection from a free end results in the reflected pulse moving back along the spring without being inverted.
