EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 3-1

Properties of WavesEdexcel IGCSE Physics pages 91 to 98

June 17th 2012

Content applying to Triple Science only is shown in red type on the next slide and is indicated on

subsequent slides by ‘TRIPLE ONLY’

Edexcel SpecificationSection 3: Wavesb) Properties of Wavesunderstand the difference between longitudinal and transverse waves and describe experiments to show longitudinal and transverse waves in, for example, ropes, springs and waterdefine amplitude, frequency, wavelength and period of a waveunderstand that waves transfer energy and information without transferring matterknow and use the relationship: wave speed = frequency × wavelength v = f × λuse the relationship: frequency = 1 / time period f = 1 / Tuse the above relationships in different contexts including sound waves and electromagnetic wavesunderstand that waves can be diffracted when they pass an edgeunderstand that waves can be diffracted through gaps,and that the extent of diffraction depends on the wavelength and the physical dimension of the gap.

Red type: Triple Science Only

Waves A wave is a means of transferring energy and information from one point to another without there being any transfer of matter between the two points.

Transverse Waves

Transverse waves are waves where the direction of vibrations is at 90° to the direction in which the wave travels.

example: water waves

wave direction

vibrations

TRANSVERSE WAVE

Longitudinal WavesLongitudinal waves are waves where the vibrations of the particles are along the direction in which the wave travels.

example: sound waves

wave direction

vibrations

LONGITUDINAL WAVE

longitudinal wave in slinky

Describing Waves1. Amplitude (A)

Amplitude is the maximum movement of the particles that make up a wave from their rest position.

amplitude

amplitude

The amplitude is the height of a crest OR the depth of a trough

rest position

2. Wavelength (λ)

Wavelength is the distance between one wave peak and the next wave peak along the path of a wave.

Wavelength is measured in metres.

Wavelength is also the distance between the bottom of one trough to the next.

wavelength

wavelength

3. Frequency (f )

Frequency is the number of wave peaks that pass a point in one second.

Frequency is measured in hertz (Hz)

1 Hz = 1 peak per second

2 Hz = 2 peaks per second and so on….

1 kilohertz (1kHz) = 1 000 Hz

1 megahertz (1MHz) = 1 000 000 Hz

1 gigahertz (1GHz) = 1 000 000 000 Hz

1 terahertz (1THz) = 1 000 000 000 000 Hz

4. Time period (T )

Time period is the time taken for a source to produce one wave.

time period = 1

frequency

and:

frequency = 1

time period

T = 1 / f

f = 1 / T

Question 1

Calculate the frequency of a wave of time period 8.0 seconds.

f = 1 / T = 1 / 8

frequency = 0.125 hertz

Question 2

Calculate the time period of a wave of frequency 50Hz.

T = 1 / f= 1 / 50

time period = 0.020 second

The wave equation

speed = frequency x wavelengthv = f x λ

speed in metres per second (m/s) wavelength in metres (m)frequency in hertz (Hz)

also: f = v ÷ λ and: λ = v ÷ f

vλf

Question 1

Calculate the speed of a water wave of wavelength 3m and frequency 6Hz.

v = f x λ

= 6Hz x 3m

speed = 18 m/s

Question 2

Calculate the frequency of a wave in water of wavelength 2.0m if its speed is 16m/s.

v = f x λ

becomes:f = v ÷ λ = 16 m/s ÷ 2m

frequency = 8 Hz

Question 3

Calculate the wavelength of a sound wave in water of frequency 300Hz if its speed is 1500m/s.

v = f x λ

becomes:

λ = v ÷ f

= 1500 m/s ÷ 300 Hz

wavelength = 5 metres

Question 4

Calculate the speed of a wave that has a wavelength of 30m and time period 0.04s.

f = 1 / T = 1 / 0.04s

f = 25 hertz

v = f x λ

= 25Hz x 30m

speed = 750 m/s

Complete:

v f λ15 Hz 4 m

330 m/s 2 m

300 000 000 m/s 1 500 m

300 000 km/s 100 MHz

Answers

3 m

200 000 Hz

165 Hz

60 m/s

DiffractionDiffraction occurs when waves spread out after passing through a gap or round an obstacle.

Sea wave diffraction

TRIPLE ONLY

Diffraction becomes more significant when the size of the gap or obstacle is reduced compared with the wavelength of the wave.

TRIPLE ONLY

Choose appropriate words to fill in the gaps below:

A wave transfers _______ without the movement of _______ from one place to another.

In a __________ wave the particle ____________ are perpendicular to the direction of wave travel.

Frequency is equal to the number of waves produced by a source in one _________. Time period is equal to the ___________ of the frequency.

The speed of a wave in m/s is equal to its __________ in metres multiplied by its __________ in hertz.

wavelength

vibrations

reciprocal

transverse

energy

second

WORD SELECTION:

matter

frequency

reciprocaltransverse energyfrequency

wavelengthvibrationssecond matter

Online SimulationsSimple demonstration of longitudinal & transverse waves - Freezeway.com Wave lab - shows simple transverse & longitudinal waves with reflection causing a stationary wave - by eChalk Wave Effects - PhET - Make waves with a dripping faucet, audio speaker, or laser! Add a second source or a pair of slits to create an interference pattern. Also shows diffraction. Virtual Ripple Tank - falstad Fifty-Fifty Game on Wave Types - by KT - Microsoft WORD Simple transverse wave - netfirms Simple longitudinal wave - netfirms Simple wave comparision - amplitude, wavelength - 7stones Fifty-Fifty Game on Wave Types - by KT - Microsoft WORD Wave on a String - PhET - Watch a string vibrate in slow motion. Wiggle the end of the string and make waves, or adjust the frequency and amplitude of an oscillator. Adjust the damping and tension. The end can be fixed, loose, or open. Vend diagram quiz comparing light and sound waves - eChalk BBC AQA GCSE Bitesize Revision: What are waves Amplitude, wavelength and frequency Wave speed

Properties of WavesNotes questions from pages 91 to 98

1. (a) What is a wave? (b) Explain the difference between a transverse and longitudinal wave (see pages 91 and 92)

2. Define what is meant by (a) amplitude; (b) wavelength; (c) frequency and (d) time period. (see pages 92 and 93)

3. (a) State the wave equation. (b) Calculate the wavelength of a radio wave of frequency 10MHz, speed 300 000km/s.(see pages 93 and 94)

4. (a) What is wave diffraction? (b) Draw diagrams showing how diffraction is affected by the wavelength of a wave. (see page 97)

5. Answer the questions on page 98.6. Verify that you can do all of the items listed in the end of chapter

checklist on page 98.

TRIPLE ONLY

Properties of WavesNotes questions from pages 91 to 98

1. (a) What is a wave? (b) Explain the difference between a transverse and longitudinal wave (see pages 91 and 92)

2. Define what is meant by (a) amplitude; (b) wavelength; (c) frequency and (d) time period. (see pages 92 and 93)

3. (a) State the wave equation. (b) Calculate the wavelength of a radio wave of frequency 10MHz, speed 300 000km/s. (see pages 93 and 94)

4. Answer questions 1, 3 and 4 on page 98

DOUBLE ONLY