On October 23rd, 2014, we updated our
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Recall…… ENERGY is the ability to push something and make it move
ENERGY can be transferred in two ways…
Transferring some matter
Using a WAVE
Types of Wave
need a medium
don’t need a medium
Waves travel in two different ways.
Transverse waves are when the displacement is at right angles to the direction of the wave… Longitudinal waves are when the displacement is parallel to the direction of the wave…
Some definitions… Amplitude (A) Wavelength ( ) distance from equilibrium to crest this is the distance between two corresponding points (crest to crest) Displacement (x) distance from equilibrium to to any point x A A Crest Trough
this is the time for one wave to pass a point. It is measured in seconds (s)
this is how many waves pass a point every second. It is measured in Hertz (Hz)
If 20 waves pass you in one minute, what is the period of the wave? 20 waves = 60 s 1 wave =3 s T= 3s Calculate the frequency of the wave.
Wave Equation λ
Nb speed isn’t frequency……………
The frequency of a wave is the number of waves passing in one second.
(or the number of times a part of the wave wiggles in one second)
The speed of a wave is the distance it travels in one second
Data Studio Sound Simulator
link to phet sound
How does ultrasound work? Ultrasonic waves are partly reflected at the boundary as they pass from one medium to another. The time taken for these reflections can be used to measure the depth of the reflecting surface. This information is used to build up a picture of the object. Ultrasound is the region of sound above 20,000Hz – it can’t be heard by humans. It can be used in pre-natal scanning:
Other uses of ultrasound 1) Echo sounding The ultrasound is reflected from the sea floor. 2) Breaking down kidney stones Ultrasonic waves break kidney stones into much smaller pieces 3) Cleaning (including teeth) Ultrasound causes dirt to vibrate off without damaging the object
SOUND Sound is produced by things vibrating. Sound travels in longitudinal waves through the air (or other medium)
You can hear sound in the range of approximately 20 Hz to 20,000 Hz .
We hear high frequency waves as high pitch
We hear large amplitude waves as loud
compression rarefaction wavelength
Drawing a Sound Wave
Sound can be analysed by an oscilloscope or a computer.
It draws a graph of the wave.
link to data studio
pressure position This is a snapshot of the whole wave at one time
pressure time This is a movie of the pressure at one place microphone
High frequency Low frequency
Reflection Pulses fixed end
Reflection of Pulses free end
Refraction of Pulses fast to slow
Refraction of Pulses slow to fast
Reflection of Waves
DEEP SHALLOW SHALLOW DEEP
Gradual Wave Refraction
K:PHYSICSPOWER POINT & VIDEOS1 Light & WavesSound
link to refraction of pulses
Diffraction When waves pass through a narrow gap they spread out or……… Diffract . The amount of diffraction depends on the size of the gap compared with the size of the wavelength Link to Diffraction animation The smaller the gap, the more diffraction The bigger the wavelength, the more diffraction
Why can you pick up radio signals better than TV? TV waves are high frequency, short wavelength.
Radio waves are low frequency, long wavelength. Long wavelengths diffract more
link to ripple tank
ripple tank + path diff
Interference of Light When light shines through a double slit interference occurs:
in phase This produces a big wave (constructive interference) when the path difference is the waves arrive
when the path difference is the waves arrive out of phase This produces no wave (destructive interference)
We will look at interference of sound waves
LINK TO phet sound
Recall the definition of path difference .
Recall the definition of constructive interference and destructive interference .
Explain what causes the loud and quiet spots.
This is what you see in the ripple tank
K:PHYSICSPOWER POINT & VIDEOS1 Light & WavesSoundwave-interference
And this is why…. http:// www.schulphysik.de/suren/Applets.html