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This comprehensive grade 12 physics module delves into the fascinating world of waves, covering their properties, superposition, interference, and interactions with boundaries. It explores both mechanical and electromagnetic waves, providing examples and illustrations to enhance understanding. The module also includes practical applications of wave phenomena, such as sound waves and light waves, and encourages students to apply mathematical formulas to calculate wave characteristics.
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GR 12 PHYSICS U4 TITLE
GR 12 PHYS M3 TITLE
GR 12 PHYS M3 ACKNOWLEDGEMENT
Flexible Open and Distance Education Papua New Guinea
Published in 2016 @ Copyright 2016, Department of Education Papua New Guinea
All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means electronic, mechanical, photocopying, recording or any other form of reproduction by any process is allowed without the prior permission of the publisher.
Printed by the Flexible, Open and Distance Education ISBN 978-9980-89-561- National Library Services of Papua New Guinea
Acknowledgements
We acknowledge the contribution of all Lower and Upper Secondary Teachers who in one way or another helped to develop this Course.
Special thanks are given to the staff of the Science Department- FODE who played active role in coordinating writing workshops, outsourcing of module writing and editing processes involving selected teachers in NCD.
We also acknowledge the professional guidance and services provided through- out the processes of writing by the members of:
Science Subject Review Committee-FODE Academic Advisory Committee-FODE Science Department- CDAD
This book was developed with the invaluable support and co-funding of the GO- PNG and World Bank.
Principal-FODE
.
GR 12 PHYS M3 INTRODUCTION
Introduction
Waves are everywhere and can be studied in terms of its forms and its method of energy transfer. But firstly, what is a wave? In simple terms, a wave is a disturbance or a vibration that transfers energy from one point to another. The transfer of energy is achieved through a medium or in some cases through vacuum (empty space). The disturbances which transfer the energy in the direction of the wave motion, travels without transferring matter. In other words, matter is not carried with the wave.
Some waves must travel through a substance known as the matter medium. It can be solid, liquid or gaseous. Sound, ocean and seismic waves are some waves that travel through a medium. As the wave travel through the medium, the particles of the medium vibrate perpendicular or parallel to the direction of the wave motion. Waves that travel through a medium are called mechanical waves.
Not all waves need a medium to travel through. Some waves are able to travel through a vacuum through the vibrations of an electric and magnetic field. Visible light, infrared rays, microwaves and radio waves are examples of waves that travel through a vacuum. Waves that do not travel through a medium or travel in vacuum are called electromagnetic waves. Note that electromagnetic waves can also travel through a medium.
There are two main types of mechanical waves. One is transverse wave and other is longitudinal wave.
Transverse waves are types of waves in which the movement of the particles of the medium is at right angle to the direction of the of the wave motion resulting in the wave having high and low energy points. The high energy point in the transverse wave is termed as the crest and the low energy point is termed as trough.
Longitudinal waves are waves in which the movement of the medium is parallel to the direction of the movement of the waves.
Waves are very important to both humans and animals. Most of our everyday activities depend on it. The transmission of information (communication) is in the form of waves. For instance you are able to listen to your audio music tracks and even watch videos on TV because of waves. Cooking, talking and seeing is also made possible because of waves.
Animals also use wave motion for body waste removal and movement (navigation) through their surroundings. For instance eels and snakes use transverse body waves to push against the water or ground to help them move and earthworms use longitudinal waves for their movement. Bats and hammerhead sharks use waves to navigate in the night.
GR 12 PHYS M4 OUTCOMES
After going through this module, you are expected to:
define wave. differentiate wave types. generate waves using ropes and springs. describe the difference between transverse and longitudinal waves in terms of particle motion. differentiate mechanical and electromagnetic waves. give examples of transverse and longitudinal waves. apply mathematical formulae in determining wave properties which include amplitude, wavelength, period and frequency. describe relationship between frequency and period from
f
draw wave diagrams from given parameters. demonstrate that waves are in phase or out of phase with respect to a reference wave. describe when two waves interfering constructively or destructively when they come together. apply mathematical formulae to calculate unknown quantities of a given wave using the wave equation: v f f
explain what light is in terms of waves.
Snell’s Law: orn sini n sinr sini
sinr n
n 1 2 2
demonstrate an understanding of practical applications of i) total internal reflection in periscopes, prisms, optic fibres and endoscope just to name a few. ii) effect of refraction; determining real depths and apparent depths of objects underwater. research and recognize that sound energy can be transmitted by waves through solid, liquid and gases.
GR 12 PHYS M3 WAVES
12.3.1 Properties of Waves
We all have observed waves in our everyday lives in many contexts. We watched water waves propagated (created) away from boats or raindrops into still pools. We often listen to sound waves (music) generated by waves created on stretched guitar strings. We are reading the words in this module by means of light, an electromagnetic wave.
To understand more about waves, we can create our own wave in the laboratory by carrying out simple activities. Waves can be propagated in the laboratory or even outdoors from simple equipment like a rope or a spring. A dish of water from the kitchen and a pebble can also be used to generate waves from which the properties of waves can also be observed.
Activity 1: Wave propagation and energy transfer.
Aims:
Materials needed: Kitchen dish, water, pebble (50 g), small floater, ruler, stop watch
Procedure:
Results:
GR 12 PHYS M3 WAVES
Figure 1 : Wave propagation using a pebble dropped onto still water.
Conclusion: The pebble at the height of 10 cm possesses gravitational potential energy (G.P.E). When the pebble was released, the G.P.E changes to kinetic energy due to the motion of the released pebble. As the pebble hits the surface of the water, the kinetic energy from the falling pebble is transferred to the surface of the water. This creates the vibration on the water surface which generates the waves. The waves then transfer the energy through the ripples (wave forms) outwards from the point of disturbance. The small floater goes up and down in the wave but does not move in the direction of the wave. This indicates that the wave motions only transfer energy and not the particles of the medium (water). The matter particles only vibrate but go back to their equilibrium position.
Remember these: The source of a wave is a vibration or oscillation. Waves transfer energy from one point to another.
Surface of water Falling pebble
Leading wave forms as pebble strikes water surface
Leading wave move outward with the energy
Original point of disturbance (^) Leading wave
D
GR 12 PHYS M3 WAVES
Electromagnetic waves Electromagnetic (EM) waves are caused by varying electric and magnetic fields. As a results of the varying magnetic and electric fields a periodic change takes place creating the EM waves. Electromagnetic waves do not require any medium for its propagation and can travel through vacuum.
Figure 3 : Electric and magnetic fields of an electromagnetic wave.
Electromagnetic radiation is the transmission of energy in the form of waves having both an electric and a magnetic component. It is not possible for a wave with just one of these components to exist. The most familiar forms of electromagnetic radiation are radio waves and light waves. Less familiar forms are infrared radiation, ultraviolet light, X–rays, and gamma rays, all of which constitute the electromagnetic spectrum.
Properties:
Two main types of wave motion
A wave that travels in a vacuum or empty space without a medium is called an electromagnetic wave.
Changing electric field
Changing magnetic field
Direction of propagation
GR 12 PHYS M3 WAVES
The two main type of wave motion are the transverse and longitudinal waves. They can be described in relations to the motion of the:
Transverse wave
Activity 2: Energy transfer from a transverse wave propagated from a rope.
Aims:
Materials needed: Rope (5m), coloured ribbon
Procedure:
Results:
Figure 4 : Transverse waveform on a rope. Conclusion:
UP
DOWN Direction of wave motion
Ribbon
GR 12 PHYS M3 WAVES
A quick series of flips sends a succession of pulses toward the post. Obviously, the rope itself does not move forward and any particle in it undergoes only up-and-down motion thus the disturbance caused at one end is conveyed to the other by a transverse wave.
Figure 7: Vibration of a spring or a rope propagates a transverse wave.
All electromagnetic waves are transverse waves; they do not require a medium and can travel in a vacuum. Transverse waves are waves in which the particles of the medium move at right angle to the wave direction.
Longitudinal wave
Activity 3: Energy transfer from a longitudinal wave propagated from a spring (slinky).
Aims:
Apparatus needed: Spring (slinky), ribbon
Procedure:
Results:
Wavelength
GR 12 PHYS M3 WAVES
Figure 8 : A boy generating longitudinal waves using a slinky.
Conclusion: The back and forth (push and pull) motion of the spring creates a disturbance. This disturbance causes the coils of the spring to vibrate and generate a compression and expansion waveform. The kinetic energy from the push and pull motion of the hand is transferred from free end of the spring to the fixed end. When the spring is moving in its back and forth waveform, noticed that the ribbon only moves parallel to the motion of the wave but does not move to the fixed end of the spring. This indicates that the wave motions only transfers energy and not the matter (spring) particles. The matter particles only vibrate but go back to their equilibrium (rest) position.
It can be concluded from the three simple activities that the source of a wave is a vibrations or oscillation. The energy from the vibration creates a disturbance and the disturbance carries the energy from one place to another through a medium or without a medium at times. It is important to note that only energy is transferred by the wave and not matter in the medium.
In a longitudinal wave, the motion of the wave energy and particle motion are parallel to each other. This means that the particles of the medium vibrate back and forth in the same direction in which the wave travels and transfer energy.
Back and forth motion
Direction of wave motion
GR 12 PHYS M3 WAVES
Energy is passed along the air molecules by the lengthways vibration of the air molecules. Thus the air molecules only move to and fro or forwards and backwards in the direction of travel of the wave. The sound energy is transferred from one molecule to another and so it travels along the wave.
Other examples of longitudinal waves include tsunami waves, earthquake, P – waves, ultra sounds, vibrations in gas, internal water waves, and waves in slink.
Now check what you have just learnt by trying out the learning activity below.
Answer the following questions on the spaces provided.
For Questions 1 – 3, fill in the missing space with the correct word.
For Questions 4 – 8, write your answers on the spaces provided.
a) __________________________________________________________________ b) __________________________________________________________________
a) __________________________________________________________________ b) __________________________________________________________________ c) __________________________________________________________________
GR 12 PHYS M3 WAVES
Refer to the diagram below to answer Question 8.
(b) What part of the wave is labelled B? _____________________ (c) What type of wave is shown in the diagram? _____________________
Thank you for completing learning activity 1. Now check your work. Answers are at the end of the module.
A
B
Displacement
Velocity of propagation
