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This review explains the difference between transverse and longitudinal waves, discussing topics such as wave transfer, wave parts, wavelength, amplitude, frequency, wave speed, reflection, and refraction.
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The way they move Review: Energy What’s the difference between a transverse and longitudinal wave? What do waves transfer? What are the high and low points of a transverse wave called? What are the parts of a longitudinal wave where the particles are spread out and close together? Crest and Trough Compression and Rarefaction
First thing’s first… • Which of these show ONE full wave? One wave has one crest and one trough
Wavelength Distance • What is length a measure of? • So what do you think a wave length is? • The distance between two waves WAVELENGTH WAVELENGTH
Measuring Wavelength • Does this tell us the distance between the two waves? • Why not? You have to measure the distance between two comparable points! (crest to crest, trough to trough, etc.)
Amplitude • The distance between the crest or trough and the wave’s resting position. • Where’s the crest? Trough? Crest Amplitude Resting Position Amplitude Trough
What does amplitude tell us about a wave? • Which of these waves would cause more damage if it hit the shore? • Which has the larger amplitude? • Which wave has more energy? THAT’S AMPLITUDE!
We’ve been looking at transverse waves…What about longitudinal? • We can relate all of the parts of a transverse wave to a longitudinal one!
We’ll start with wavelength… The distance from crest to crest or trough to trough • In a transverse wave: • But there aren’t any crests or troughs in a longitudinal wave! WAVELENGTH WAVELENGTH
So we look at the compressions and rarefactions! • Compressions = Crests • Rarefactions = Troughs • Now we can find the wavelength • Compression to compression • Rarefaction to rarefaction
On to amplitude… The distance from crest or trough to the wave's resting point • In a transverse wave: • We now know that compressions and rarefactions are like the crests and troughs, but it’s hard to find a longitudinal wave’s resting point.
Amplitude • For the amplitude of a longitudinal wave, we look at how compressed or how rarefied the spring or particles are. • The more compressed or rarefied it is, the higher the amplitude and vice versa.
Frequency • If your friend comes over to your house “frequently”, how often do they come over? • Can you take a guess as to what the “frequency” of a wave is? • The frequency of a wave tells us the number of waves that are produced in a certain amount of time.
We need to know how many waves are being produced in 10 seconds. • How can you find the frequency of this wave? • Step 1: pick a point. • Step 2: count the waves that pass that point in 10 seconds.
What about Energy? Waves with _________________ frequency have more energy. a higher Which wave did you have to put more energy into to create?
What is the unit for frequency? • Frequency is measured in Hertz (Hz). • If one full wave passes a point every second, it has a frequency of 1 Hz. • 1 wave per second (1 wave/1 sec.) • What is the frequency if three waves pass a point every second? • 3 Hz. (3 waves/1 second) • What is the frequency if six waves pass a point every three seconds? • 2 Hz. (6 waves/3 seconds)
Wave Speed • There are two ways to calculate wave speed. • Option 1: time how long a wave takes to get from point A to point B. A B
Wave speed = wavelength x frequency • Option 2: Use the following formula Wave Speed = 8 meters/second Wavelength – 2 meters Frequency – 4 Hz. (4 waves pass every second)
Wave speed is affected by several factors • The type of wave • Example: electromagnetic waves always travel at the same speed in a vacuum (300,000 km/s – the speed of light) • The medium the wave is moving through • If you start two waves in a pan, one with water and one with corn syrup, which will reach the other side of the pan first? • Another example is popping your knuckles underwater as opposed to above water.
Reflection • Law of Reflection • The angle of incidence equals the angle of reflection
Image position • You think in straight lines! • The image is located behind the mirror.
Refraction • Sudden change in direction of a wave as it changes speed. • It must enter obliquely to change direction! • Which direction does it bend as it slows?
Refraction • In both cases the speed of the wave has decreased. This is indicated by the decrease in wavelength!
Refraction • In which medium does light travel faster? (glass rod appears bent)
Refraction • In simple terms, refraction is caused when a wave moves from one type of medium to another that has a different density. This makes objects between them look different.