Waves are simply a way that energy is transferred from one place to another.
Whether they are mechanical waves such as waves in the ocean, a wave in a spring and sound waves, or electromagnetic waves, such as radio waves for x-rays, they all share similar features and properties. In these series of lessons, we discuss their features and importantly what happens when waves interact.
Start by watching this video which gives a broad overview of the study of waves and allows you to see how the various concepts are into related. It may also be useful to watch this video as a review exercise after you have studied all the key components involving wave physics.
Whether they are mechanical waves such as waves in the ocean, a wave in a spring and sound waves, or electromagnetic waves, such as radio waves for x-rays, they all share similar features and properties. In these series of lessons, we discuss their features and importantly what happens when waves interact.
Start by watching this video which gives a broad overview of the study of waves and allows you to see how the various concepts are into related. It may also be useful to watch this video as a review exercise after you have studied all the key components involving wave physics.
Transverse WavesTransverse Waves are waves where the particles that carry the wave in the medium, travel perpendicular to the direction of the wave. When viewed, as a still image, they take a sinusoidal shape. (There is a reason for this and will discussed in a future video)
As a result it has a characteristic 'top' of the wave, called the crest and a 'bottom' called the trough. The video reviews the basic features of a transverse wave and also examine the simple wave equation which determines the velocity of the wave |
|
Test your understanding
Interactive
The following animation, from pHET, allow you to play with the same animation in the video
The following animation, from pHET, allow you to play with the same animation in the video
To simplify things, start with no damping and have the wave 'leave the window' which avoids reflection issues and thus interference, which is discussed later.
- Click 'oscillate'. You will notice the the piston will have a regular period (time it taks for once cycle) and thus a regular frequency (number of cycles per second)
The green dots allow you to visualize that ALL particle do the same thing - undergoing periodic motion. The only difference is is that their phases is different - You should notice though that there are particle that are completely "in sync" (that is, they are in phase). They will be separated by a distance of one wavelength.
- Increase the frequency. What do you notice about the wavelength? What do you notice about the speed of the wave?
|
|
Longitudinal WavesLongitudinal waves are waves where the particles of the medium vibrate parallel to the direction of the wave. Instead of crests and troughs, they are marked by the presence of compressions and rarefactions.
In the following video you will see a demonstration and explanation of longitudinal waves using a slinky. Also demonstrated is how sound requires a medium. |
But wait, there's more...
And then there's an example of a torsional wave, where the medium rotates about a circle whose plane is perpendicular to the wave velocity
|
Some waves are more complex and cannot be described as either transverse or longitudinal waves. A good example is the surface wave. In the case to the left, the wave appears as a transverse wave, but unlike a transverse wave, the particles moved periodically in circles, the size of which is dependent on the depth to the surface.
|
Some problems to try
1) 3m/s 2) 1.33m 3) 0.67m 4) 2.91m 5) 0.0207- 20.7 m 6) 3m
- A wave in the ocean has a wavelength of 1.5 m and a period of 0.5 seconds. What is the wave speed?
- The speed of sound is 340 m/s. If a piano places middle C, 256 Hz, what is its corresponding wavelength?
- A wave in a pool is seen to travel at 1 m/s. If it hits the side at a rate of 1.5 per second, what is the wavelength?
- Radio station 103.1 has a frequency of 103.1 MHz, hence its number. What is the wavelength of the wave, given that its speed is 300,000,000 m/s?
- Sound waves travel in air at about 330 m/s. If the human ear is sensitive to frequencies from about 16 Hz to 16 kHz, to what range of wavelengths does this correspond? (HINT: work out λ for one frequency, then do the other)
- VHF television channels transmit at frequencies of the order of 100 MHz.
- What is the corresponding wavelength? (v = 300,000,000 m/s)
1) 3m/s 2) 1.33m 3) 0.67m 4) 2.91m 5) 0.0207- 20.7 m 6) 3m
Interactive
Let's summarise the two key wave types by playing with the animation
Let's summarise the two key wave types by playing with the animation
