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Physics Chapter 12 - Waves (Properties of Waves ((rest position - the…
Physics Chapter 12 - Waves
Properties of Waves
sound waves cause air particles to vibrate back and forth
ripples cause water particles to vibrate up and down
In longitudinal waves, the vibrations are parallel to the direction of wave travel. In transverse waves, the vibrations are at right angles to the direction of wave travel.
Mechanical waves cause oscillations of particles in a solid, liquid or gas and must have a medium to travel through. Electromagnetic waves cause oscillations in electrical and magnetic fields.
rest position - the undisturbed position of particles or fields when they are not vibrating
displacement - the distance that a certain point in the medium has moved from its rest position
peak - the highest point above the rest position
trough - the lowest point below the rest position
amplitude - the maximum displacement of a point of a wave from its rest position
wavelength - distance covered by a full cycle of the wave, usually measured from peak to peak, or trough to trough
time period - the time taken for a full cycle of the wave, usually measured from peak to peak, or trough to trough
frequency - the number of waves passing a point each second
Transverse and Longitudinal Waves
rarefaction's are regions of low pressure due to particles being spread further apart
In transverse waves, the vibrations are at right angles to the direction of wave travel.
Examples of transverse waves include:
ripples on the surface of water
vibrations in a guitar string
a Mexican wave in a sports stadium
electromagnetic waves - eg light waves, microwaves, radio waves
seismic S-waves
Compression's are regions of high pressure due to particles being close together
none of the particles are transported along a transverse wave. The particles move up and down as the wave is transmitted through the medium.
In longitudinal waves, the vibrations are parallel to the direction of wave travel.
Examples of longitudinal waves include:
sound waves
ultrasound waves
seismic P-waves
Reflection and Refraction
The law of reflection states that:
angle of incidence = angle of reflection
If a surface is rough, diffuse reflection happens. Instead of forming an image, the reflected light is scattered in all directions. This may cause a distorted image of the object, as occurs with rippling water, or no image at all. Each individual reflection still obeys the law of reflection, but the different parts of the rough surface are at different angles.
Set up a ray box, slit and lens so that a narrow ray of light is produced.
Place a 30 centimetre (cm) ruler near the middle of a piece of plain A3 paper. Draw a straight line parallel to its longer sides. Use a protractor to draw a second line at right angles to this line. Label this line with an ‘N’ for ‘normal’.
Place the longest side of a rectangular acrylic polymer block against the first line. With the normal near the middle of the block, carefully draw around the block without moving it.
Use the ray box to shine a ray of light at the point where the normal meets the block. This is the incident ray.
The angle between the normal and the incident ray is called the angle of incidence. Move the ray box or paper to change the angle of incidence. The aim is to see a clear ray reflected from the surface of the block and another clear ray leaving the opposite face of the block.
Using a pencil on the paper, mark the path of:
the incident ray with a cross
the reflected ray with a cross
the ray that leaves the block with two crosses - one near the block and the other further away
Remove the block. Join the crosses to show the paths of the light rays.
Repeat steps 2 to 7 for a rectangular glass block.
Measure the angle of incidence, angle of refraction and angle of reflection for each block.
Sound and Ultrasound
they are transverse waves
The frequency of a sound wave is related to the pitch that is heard:
high frequency sound waves are high pitched
low frequency sound waves are low pitched
The amplitude of a sound wave is related to the volume of the sound:
high amplitude sound waves are loud
low amplitude sound waves are quiet
Lenses
Black Body Radiation
