NEW MODULE: WAVES

By the end of the lesson you should be able to explain/know: The difference between longitudinal and transverse waves How to describe fully a wave What amplitude, frequency, wave speed and wavelength mean. They need to copy down these lesson objectives At the end of the lesson, there is another slide which has the same thing on but is phrased in terms of lesson outcomes – so they can compare and think about whether they have understood.

Medium A medium is a substance or material that carries the wave. The wave medium is not the wave and it doesn't make the wave; it merely carries or transports the wave from its source to other locations. 

Medium cont… In the case of our slinky wave, the medium through that the wave travels is the slinky coils. In the case of a water wave in the ocean, the medium through which the wave travels is the ocean water. In the case of a sound wave moving from the church choir to the pews, the medium through which the sound wave travels is the air in the room. And in the case of the stadium wave, the medium through which the stadium wave travels is the fans that are in the stadium.

What are waves? transverse longitudinal Waves transfer energy They can be transverse or longitudinal: transverse longitudinal The motion of the wave is at a right angle to the direction of the wave The motion of the wave is in the same direction as the wave e.g. sound waves e.g. light waves

What are waves? They always do 3 things: reflect refract diffract

Longitudinal Waves

Make a longitudinal wave using a spring between two people like this : LONGITUDINAL WAVES Make a longitudinal wave using a spring between two people like this : Label compression and rarefaction – stretching and squashing of the wave – higher and lower frequency What type of energy is the wave transferring? In which direction is the energy moving? In which direction is each part of the spring moving? [put a marker on the spring to help you see] kinetic

A compression is a region in a longitudinal wave where the particles are closest together. A rarefaction is a region in a longitudinal wave where the particles are furthest apart.

When you speak to someone, the air vibrates as a longitudinal wave : LONGITUDINAL WAVES You should have noticed that each part of the wave moves in the same direction as the direction the energy is moving in: particle movement energy movement When you speak to someone, the air vibrates as a longitudinal wave :

Transverse Waves

TRANSVERSE WAVES kinetic What type of energy is the wave transferring? In which direction is the energy moving? In which direction is each part of the rope moving? [put a marker on the rope to help you see] kinetic

Transverse Waves Each part of the wave moves at right angles [90º] to the direction the energy is moving in: Particle Movement Energy Movement

Measuring Waves What sort of waves are these? transverse or longitudinal? a wave in the sea? a wave in some string? A sound wave? A wave in a slinky spring? A light wave?

Describing Waves

Drawing a wave

Amplitude Amplitude: is the maximum disturbance caused by a wave (the height of a peak). This is usually measured in metres. Or: The height of a wave from its middle to its peak

Wavelength Wavelength: the distance between any two peaks. This is usually measured in metres. Or The distance from one point on a wave to the same point on the next wave

Frequency

Frequency Frequency refers to how many waves are made per time interval, measured in Hertz (Hz) This is usually described as how many waves are made per second, or as cycles per second.

High or Low Frequency?

Animation to demonstrate wavelength, amplitude and frequency

Wave Speed

speed = frequency x wavelength Speed of waves The speed of a wave is: speed = frequency x wavelength Speed is measured in metres per second (m/s) Frequency is measured in _____ Wavelength is measured in ______ If a wave has a wavelength of 2 metres and a frequency of 5 Hz, what is its speed? Hz m

 Energy and Waves : A Question The photograph shows waves travelling across the surface of a pond. 1m  1) Is this an example of a transverse or longitudinal wave? transverse