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Topic 3 Waves
This lesson
• What is a wave?
• Longitudinal and transverse waves
• Amplitude, wavelength, frequency and period of a wave
• The relationship between frequency and period
• The wave equation
What is a wave?
YouTube - Water bubble in Space (zero gravity)
Waves
Waves can transfer energy and information without a net motion of the medium through which they travel.
They involve vibrations (oscillations) of some sort.
Waves
Waves can transfer energy and information without a net motion of the medium through which they travel.
They involve vibrations (oscillations) of some sort.
Can you do something very boring and traditional………
Can you copy this please?
Rays
Rays highlight the direction of energy transfer.
Transverse waves
The oscillations are perpendicular to the direction of energy transfer.
Direction of energy transfer
oscillation
Transverse waves
peak
trough
Transverse waves
• Water ripples
• Light
• On a rope/slinky
• Earthquake
Longitudinal waves
The oscillations are parallel to the direction of energy transfer.
Direction of energy transfer
oscillation
Longitudianl waves
compression
rarefraction
Longitudinal waves
• Sound
• Slinky
• Earthquake
Wave measurements
Amplitude - A
The maximum displacement from the mean position.
amplitude
Period - T
The time taken (in seconds) for one complete oscillation. It is also the time taken for a complete wave to pass a given point.
One complete wave
Frequency - f
The number of oscillations in one second. Measured in Hertz.
50 Hz = 50 vibrations/waves/oscillations in one second.
Period and frequency
Period and frequency are reciprocals of each other
f = 1/T T = 1/f
Wavelength - λ
The length of one complete wave.
wavelength
Wave speed - v
The speed at which the wave fronts pass a stationary observer.
330 m.s-1
YouTube - Bill Nye the Science Guy - 51: Waves 1/3
The Wave Equation
The time taken for one complete oscillation is the period T. In this time, the wave will have moved one wavelength λ.
The speed of the wave therefore is distance/time
v = λ/T = fλv
λf x
The Wave Equation
The time taken for one complete oscillation is the period T. In this time, the wave will have moved one wavelength λ.
The speed of the wave therefore is distance/time
v = fλv
λf xCan you copy this part please?
1) A water wave has a frequency of 2Hz and a wavelength of 0.3m. How fast is it moving?
2) A water wave travels through a pond with a speed of 1m/s and a frequency of 5Hz. What is the wavelength of the waves?
3) The speed of sound is 330m/s (in air). When Dave hears this sound his ear vibrates 660 times a second. What was the wavelength of the sound?
4) Purple light has a wavelength of around 6x10-7m and a frequency of 5x1014Hz. What is the speed of purple light?
Some example wave equation questions
0.2m
0.5m
0.6m/s
3x108m/s
Wave equation questions
vλf x
Let’s try some questions!
Yay!!
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