WAVES: Waves transfer energy from one point to another without transferring matter.

Transverse waves are wave in which the vibrations of the particles or medium in which the wave travels are at right anglesor perpendicular to the direction in which the wave travels

The distance between two successive crests or two successive troughs is thewavelength for a transverse wave.The height of the crest from the undisturbed water position or the depth of the trough from the undisturbed water position is theamplitudeof the wave

Longitudinal wavesare waves in which the vibrations of the particles or medium in which the wave travels are in the same direction as to that in which the wave travels.

This diagram above shows the side view of a sound wave. A soundwave is a longitudinal wave. It is made up of regions where the air molecules are close together and have a higher particle density known ascompressionsand of regions where the air molecules are farther apart and have a low particle density calledrarefactions. In a sound wave the region of compression is at a slightly higher pressure due to the air molecules being pushed together whereas the region of rarefaction is at a slightly lower pressure as the air molecules are farther apart.

The wavelength of a longitudinal waveis the distance between successive compressions or the distance between successive rarefactions.Theamplitudeis the maximum distance the vibrating particle travels from its undisturbed distance.

The frequency of a wave is a measure of the number of waves made by a source each second, or the number of waves that pass through a particular point in the medium each second. Frequency is measured in units called Hertz (Hz) which is the number of number of wave cycles per second.

Note: the speed of a wave does not depend on the frequency or the wavelength. As the frequency increases the wavelength decrease so from the wave equation it can be determined that the overall wave speed will remain the same.

When waves strike a material boundary i.e. go from one medium to another the following may happen:

Reflection / The wave can bounce back e.g. light striking a mirror
When waves undergo reflection the angle the incoming waves make with the surface is equal to the angle of the reflected waves. This is theLaw of Reflectionand can be written as;
The angle of incidence = the angle of reflection
Refraction: / The wave can change speed and direction e.g. light travelling from air into water The speed at which a wave travels is dependent upon the medium in which it travels along or through. The speed of a wave changes when a wave moves from one medium to another. This change in wave speed is accompanied by a change in wavelength and change in direction. It is this change of direction or bending of the wave as it passes from one medium to another that is called refraction.
Absorption: / The wave can give up its energy e.g. microwaves are absorbed by food in a microwave oven.

Further studying:

  • Pitch is a term used to describe how high or low a note a being played by a musical instrument or sung seems to be.The pitch of a note depends on the frequency of the source of the sound
  • A high frequency produces a high pitched note and a low frequency produces a low pitched note.
  • Loudness depends on the amplitude of the sound wave.The larger the amplitude the more energy the sound wave contains therefore the louder the sound.

PRACTICE WAVE Problems:

1. How many complete waves are shown in the diagram?

2. If the distance from point A to point B in the diagram is 60 cm, then the wavelength is ____.

3. What is the frequency of a wave that has a speed of 0.4 m/s and a wavelength of 0.020 meter?

4. A pirate ship is trying to locate a treasure lost on the floor of the ocean. They use a sonar device to locate it. The sound wave they sent out took 4 seconds to travel from sonar device to the treasure and back, what is the depth of the sunken treasure?

(Hint: the speed of the sound wave is 1530m/s )

5. The main factor which effects the speed of a sound wave is the ____.

6. As a wave travels into a medium in which its speed increases, its wavelength ____.

7. A vibrating object with a frequency of 200 Hz produces sound which travels through air at 360 m/s. The number of meters separating the adjacent compressions in the sound wave ( the wavelength) is ____.

8.A girl moves away from a source of sound at a constant speed. Compared to the frequency of the sound wave produced by the source, the frequency of the sound wave heard by the girl is ____.

Fill in this table: Don’t forget units!

Time (Secs) Waves / Wavelength (m) / Frequency (Hz) / Speed 1
d/t / Speed 2
V=λf
4 s / 8m
5 s / .5m / 25Hz

9. Why can’t sound travel in space?

10. How can you tell how far away a lightening strike is when you see the lightening and then hear the thunder?