Cambridge CIE IGCSE Physics Waves PDF

Head to www.savemyexams.com for more awesome resources Cambridge (CIE) IGCSE Physics Your notes General Properties of Waves Contents Features of Waves The Wave Equation Transverse & Longitudinal Waves Wave Behaviour...

Head to www.savemyexams.com for more awesome resources Cambridge (CIE) IGCSE Physics Your notes General Properties of Waves Contents Features of Waves The Wave Equation Transverse & Longitudinal Waves Wave Behaviour Ripple Tank Page 1 of 31 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Features of Waves Your notes Waves & energy transfer Waves transfer energy without transferring matter For sound waves, this means it is the wave and not the air molecules (the matter) itself that travels Objects floating on water provide evidence that waves only transfer energy and not matter It is possible to see objects on the surface of the water bob up and down but not change their position This is because the wave and not the water (the matter) itself that travels Waves are described as oscillations or vibrations about a fixed point For example, ripples cause particles of water to oscillate up and down Sound waves cause particles of air to vibrate back and forth Worked Example The diagram below shows a toy duck bobbing up and down on top of the surface of some water, as waves pass it underneath. Use this image Explain how the toy duck demonstrates that waves do not transfer matter. Page 2 of 31 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Answer: Your notes The plastic duck moves up and down but does not travel with the wave along the surface of the water The water waves transfer energy, but the water particles do not move This means when a wave travels between two points, no matter travels with it, the points on the wave vibrate back and forth about fixed positions Objects floating on the water bob up and down when waves pass under them, demonstrating that there is no movement of matter in the direction of the wave, only energy Examiner Tips and Tricks There is a key distinction between the particles (or oscillations) of a wave, and the wave itself. The motion of the wave causes the particles to move. The particles themselves are not the wave. Wave motion Wave motion can be illustrated by: vibrations in ropes and springs experiments using water waves Wave vibrations Page 3 of 31 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Use this image Waves can be shown through vibrations in ropes or springs Properties of waves can be observed using water waves in a ripple tank Properties include frequency, wavelength and wave speed as explained in the next section Wave motion in a ripple tank Page 4 of 31 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Use this image Wave motion of water waves may be demonstrated using a ripple tank Features of a Wave When describing wave motion, there are several terms which are important to know, including: Wavefront Wavelength Frequency Page 5 of 31 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Crest (peak) Trough Your notes Amplitude Wave speed Wavefront Wavefronts are a useful way of picturing waves from above: each wavefront is used to represent a single wave The image below illustrates how wavefronts are visualised: The arrow shows the direction the wave is moving and is sometimes called a ray The space between each wavefront represents the wavelength When the wavefronts are close together, this represents a wave with a short wavelength When the wavefronts are far apart, this represents a wave with a long wavelength Wavefronts are viewed from above Page 6 of 31 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Use this image Diagram showing a wave moving to the right, drawn as a series of wavefronts Your notes Wavelength Wavelength is defined as: The distance from one point on the wave to the same point on the next wave In a transverse wave: The wavelength can be measured from one peak to the next peak In a longitudinal wave The wavelength can be measured from the centre of one compression to the centre of the next The wavelength is given the symbol λ (lambda) and is measured in metres (m) The distance along a wave is typically put on the x-axis of a wave diagram Wavelength and amplitude of a transverse wave Use this image Diagram showing the amplitude and wavelength of a wave Frequency Frequency is defined as: Page 7 of 31 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources The number of waves passing a point in a second Frequency is given by the symbol f and is measured in Hertz (Hz) Your notes Crests & troughs A crest, or a peak, is defined as: The highest point on a wave above the equilibrium, or rest position A trough is defined as The lowest point on a wave below the equilibrium, or rest, position Wave crests and troughs Use this image Diagram showing a crest and a trough on a transverse wave Amplitude Page 8 of 31 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Amplitude is defined as: The distance from the undisturbed position to the peak or trough of a wave Your notes It is given the symbol A and is measured in metres (m) Amplitude is the maximum or minimum displacement from the undisturbed position Wave speed Wave speed is the speed at which energy is transferred through a medium Wave speed is defined as: The distance travelled by a wave each second The equation used to calculate wave speed is explained in The wave equation Worked Example Small water waves are created in a ripple tank by a wooden bar. The wooden bar vibrates up and down hitting the surface of the water. The diagram below shows a cross-section of the ripple tank and water. Use this image Identify the letter which shows: a) The amplitude of a water wave. b) The wavelength of the water wave. Page 9 of 31 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Answer: Your notes Part (a) Step 1: Recall the definition of amplitude Amplitude = The distance from the undisturbed position to the peak or trough of a wave Step 2: Mark the undisturbed position on the wave This is the centre of the wave Use this image Step 3: Identify the arrow between the undisturbed position and a peak The amplitude is shown by arrow D Part (b) Step 1: Recall the definition of wavelength Wavelength = The distance from one point on the wave to the same point on the next wave Step 2: Draw lines on each horizontal arrow This helps to identify the points on the wave the arrows are referring to Use this image Step 3: Identify the arrow between two of the same points on the wave Page 10 of 31 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources The wavelength is shown by arrow C Your notes Page 11 of 31 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources The Wave Equation Your notes The wave equation The equation used to calculate wave speed is: v=f ×λ Where: v = wave speed, measured in metres per second (m/s) f = wave frequency, measured in hertz (Hz) λ = wavelength, measured in metres (m) Wave speed is defined as: The distance travelled by a wave each second Wave speed is the speed at which energy is transferred through a medium Transverse and longitudinal waves both obey the wave equation Wave speed formula triangle Page 12 of 31 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes For more information on how to use a formula triangle refer to the revision note on speed & velocity Worked Example A wave in a pond has a speed of 0.15 m/s and a time period of 2 seconds. Calculate: a) The frequency of the wave b) The wavelength of the wave Answer: Part (a) Step 1: List the known quantities Page 13 of 31 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Time period, T = 2 s Step 2: State the equation relating time period and frequency Your notes 1 T= f Step 3: Rearrange for frequency, f, and calculate the answer 1 1 f = = T 2 Frequency, f = 0.5 Hz Part (b) Step 1: List the known quantities Wave speed, v = 0.15 m/s Frequency, f = 0.5 Hz Step 2: Write out the wave speed equation v=f ×λ Step 3: Rearrange the equation to calculate the wavelength v λ= f Step 4: Use the frequency you calculated in part (a) and put the values into the equation 0. 15 λ= 0.5 Wavelength, λ = 0.30 m Examiner Tips and Tricks When stating equations make sure you use the right letters. For example, use λ for wavelength, not L or W If you can’t remember the correct letters, then just state the word equations Be careful with units: wavelength is usually measured in metres and speed in m/s, but if the wavelength is given in cm you might have to provide the speed in cm/s Page 14 of 31 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Likewise, watch out for the frequency given in kHz: 1 kHz = 1000 Hz Your notes Page 15 of 31 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Transverse & Longitudinal Waves Your notes Transverse waves Waves can exist as one of two types: Transverse Longitudinal Transverse waves Transverse waves are defined as: Waves where the direction of vibration is at right angles to the direction of propagation For a transverse wave: The energy transfer is perpendicular to the wave motion They can move in solids, and on the surface of liquids but not in liquids or gases They can move in a vacuum Transverse wave motion Transverse waves can be seen in a rope when it is moved quickly up and down Page 16 of 31 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Examples of waves that can be modelled as transverse are: Electromagnetic waves (such as radiowaves, visible light, X-rays etc) Your notes Ripples on the surface of water Seismic S-waves (secondary earthquake waves) Longitudinal waves Longitudinal waves are defined as: Waves where the direction of vibration is parallel to the direction of propagation For a longitudinal wave: The energy transfer is in the same direction as the wave motion They can move in solids, liquids and gases They can not move in a vacuum (since there are no particles) The key features of a longitudinal wave are where the points are: Close together, called compressions Spaced apart, called rarefactions Longitudinal wave motion Longitudinal waves can be seen in a slinky spring when it is moved quickly backwards and forwards Examples of waves that can be modelled as longitudinal waves are: Sound waves Page 17 of 31 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Seismic P-waves (primary earthquake waves) Difference between transverse and longitudinal waves Your notes Comparing transverse and longitudinal waves Property Transverse waves Longitudinal waves Structure Peaks and troughs Compressions and rarefactions Vibration Right angles to the direction of energy Parallel to the direction of energy transfer transfer Vacuum Only electromagnetic waves can travel in a Cannot travel in a vacuum vacuum Material Can move in solids and the surfaces of Can move in solids, liquids and gases liquids Density A constant density The density of the wave changes Pressure Has a constant pressure Pressure in the wave changes Speed of Depends on the material the wave is Depends on the material the wave is wave travelling in travelling in Examiner Tips and Tricks The key difference between transverse and longitudinal waves is the direction of the vibrations with respect to the direction of the wave itself. For transverse waves, these are perpendicular to each other, whilst for longitudinal waves, these are parallel. Page 18 of 31 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Wave Behaviour Your notes Reflection, refraction & diffraction All waves, whether transverse or longitudinal, can undergo: reflection at a plane surface refraction due to a change of speed diffraction through a narrow gap In optics, a transparent material is called a medium When referring to more than one medium these are called media Angles of light are measured from an imaginary line called the normal The normal is always drawn perpendicular to the boundary between two media Reflection Reflection occurs when: A wave hits a boundary between two media at a plane surface and does not pass through, but instead stays in the original medium An example of reflection Page 19 of 31 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes An identical image of the tree is seen in the water due to reflection Refraction When waves enter a different medium, their speed can change This effect is called refraction and it occurs when: A wave passes a boundary between two different transparent media and undergoes a change in speed When a wave refracts, as well as a change in speed, the wave also undergoes: A change in wavelength (but frequency stays the same) A change in direction An example of refraction Page 20 of 31 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Waves can change direction when moving between materials with different densities The direction of the incident and refracted rays are also taken from the normal line If the waves slow down, they will bunch together, causing the wavelength to decrease The waves will also start to turn slightly towards the normal If the waves speed up then they will spread out, causing the wavelength to increase The waves will also turn slightly away from the normal Diffraction When waves pass through a narrow gap, the waves spread out This effect is called diffraction Waves diffracting through a narrow gap Page 21 of 31 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Diffraction: when a wave passes through a narrow gap, it spreads out Examiner Tips and Tricks When drawing waves being reflected take care to: Make sure that the angle of incidence is equal to the angle of reflection Keep the wavelength of the waves the same Similarly, when waves are diffracted the wavelength remains constant. Refraction is the only wave effect in which the wavelength changes. Remember: Refraction is the name given to the change in the speed of a wave when it passes from one medium to another. The change in direction is a consequence of this. Factors affecting diffraction Extended tier only The extent of diffraction depends on the width of the gap compared with the wavelength of the waves Diffraction is the most prominent when the width of the slit is approximately equal to the wavelength Page 22 of 31 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources As the gap gets bigger, the effect gradually gets less pronounced until, in the case that the gap is very much larger than the wavelength, the waves no longer spread out at all Effect of gap size on diffraction Your notes The size of the gap (compared to the wavelength) affects how much the waves spread out Diffraction can also occur when waves curve around an edge or barrier The waves spread out to fill the gap behind the object The extent of this diffraction also depends upon the wavelength of the waves The greater the wavelength then the greater the diffraction Effect of wavelength on diffraction around an edge Page 23 of 31 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes When a wave goes past the edge of a barrier, the waves can curve around it. Shorter wavelengths undergo less diffraction than longer wavelengths Page 24 of 31 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Ripple Tank Your notes Investigating waves with a ripple tank Ripple tanks are commonly used in experiments to demonstrate the following properties of water waves: Reflection at a plane surface Refraction due to a change in speed caused by a change in depth Diffraction due to a gap Diffraction due to an edge Ripple tank experimental set-up Page 25 of 31 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Reflection, refraction and diffraction can be demonstrated using a ripple tank Wavefronts from the transverse water surface waves can be viewed and analysed on the screen illuminated to show below the tank Investigating Reflection Wavefronts are reflected off a metal bar (plane surface) placed in the water of the ripple tank When the bar is placed at an angle to the wavefronts of the waves generated by the paddle reflect according to the Law of reflection Page 26 of 31 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Diagram of reflected wavefronts in a ripple tank Your notes Incident wavefronts are reflected at 90 degrees against a barrier Reflected wavefronts in a ripple tank Page 27 of 31 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Wavefronts of incident and reflected waves form right angles to each other Investigating refraction Refraction can be shown by placing a glass block in the tank The glass block should sit below the surface of the water and cover only some of the tank floor The depth of water becomes shallower where the glass block is placed Since speed depends on depth, the ripples slow down when travelling over the block The water surface waves slow down when passing from deep to shallow water in the ripple tank Refracted wavefronts in a ripple tank Page 28 of 31 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes When water waves travel from deep areas to shallow areas they slow down Investigating diffraction Diffraction can be shown in a ripple tank by placing small barriers with a gap or an edge in the tank The amount of Diffraction that occurs can be changed by changing the wavelength of the waves compared to the gap size Changing the gap size for diffraction in a ripple tank Page 29 of 31 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes When the gap size is bigger than the wavelength less diffraction occurs and the waves spread out less after passing through Changing the wavelength of waves in the ripple tank The motor creates the up-and-down movement of the paddle The frequency of the motor affects the wavelength of the waves generated by the paddle The diagram below shows how the wavelengths differ with frequency in a ripple tank The higher the frequency of the motor, the shorter the wavelength The lower the frequency of the motor, the longer the wavelength Wavelength and frequency of waves in a ripple tank Page 30 of 31 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Ripple tank patterns for low and high-frequency vibration Page 31 of 31 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers