Waves

A wave is a rhythmic disturbance that carries energy through matter or space.

Water waves, sound waves, and the waves that travel down a rope or spring are types of mechanical waves. Mechanical waves require a medium.

A wave pulse is a single bump or disturbance that travels through a medium. If the disturbance is continuous, a continuous wave is generated.

It is important to distinguish between the motion of the wave and the motion of the individual particles in the wave. In general, waves travel from place to place, but the particles in a wave oscillate back and forth about one location.

For example, a "wave" at a ballgame travels around the stadium, but the individual people making up the wave simply stand up and sit down.

Waves transmit ENERGY but not MATTER.

Transverse Waves• The medium (the material the energy/wave travels in) and the

energy travel perpendicular to each other.• The crest/troughs are the high/low points along the medium.• The amplitude refers to the energy that the wave has. Larger

amplitude= more energy.• The wavelength can be determined by measuring the distance

from ANY point on the wave, and the next point just like it. For example, crest to crest or trough to trough.

wavelength

Compressional/Longitudinal Wave• The medium and the energy travel parallel to each other. The medium travels back

and forth and really goes no where ultimately. But the energy does travel horizontally as well and does go somewhere.

• The dense regions are referred to as compressions and the less dense regions, expansions, are more often referred to as rarefactions.

• The wavelength can be measured in the same way, from any point to the next point just like it. For example, from the start of one compression to the start of the next compression.

• Amplitude in a compressional wave can be determined by how dense the compressions are. The more dense the more energy or amplitude.

Examples of Compressional and Transverse Waves

Sound Wave on a Rope

Example of Combination Waves

Surface Waves& Seismic

(Earthquake) Waves

Calculating the Velocity of a wave

v=λf

v- velocity (m/s)λ- wavelength (m)f- frequency (Hz= 1/s)

v= Δd/ Δt

v- velocity (m/s)Δd- distance wave travels (m)Δt- time (s)

Period vs FrequencyThe PERIOD is defined as the number of seconds it takes to complete just one wave cycle. It should be measured in seconds. If not, convert with a smile on your face.

The FREQUENCY is defined as the numbers of wave cycles that occur in just one second. The unit would be cycles/s. However, cycles isn’t technically a unit so the real unit is 1/s which also happens to be the same thing as Hertz. Hz=1/s

The two words are inverse or opposites of each other. So,

T= 1/f and f=1/T

Waves at BoundariesWhen a wave hits a boundary, a portion of the energy (wave) will be transmitted to the new medium and a portion will be reflected. The more dense the boundary, the more reflection you will get.

Picture “a” shows an erect incident wave headed toward a very dense boundary. Picture “b” shows the inverted reflected wave….almost 100% reflection. Remember, the more dense the boundary, the more reflection you will get.

Wave Hitting a Less Dense Medium

In this case, we have a more dense spring connected to less dense spring. Notice in picture “b” the reflected wave is still erect.

BIG IDEA: When an incident wave hits a boundary that is more dense than the medium it is in, it will reflect with opposite amplitude. When an incident wave hits a boundary that is less dense than the medium it is in, it will reflect with the same amplitude.

Law of ReflectionThe angle of incidence = the angle of reflection.

Superposition of WavesSuppose a pulse traveling down a spring meets a reflected pulse coming back. In this case, two waves exist in the same place in the medium at the same time. Each wave affects the medium independently. The displacement of a medium caused by two or more waves is the algebraic sum of the displacements caused by the individual waves. This is calledthe principle of superposition. In other words, two or more waves can combine to form a new wave. If the waves are in opposite directions, they can cancel or form a new wave of less or greater amplitude. The result of the superposition of two or more waves is called interference.

Destructive InterferenceThe superposition of waves with opposite amplitudes

causes destructive interference.

When the pulses meet and are in the same location, the displacement is zero. Point N, which doesn’t move at all, is

called a node.

Constructive InterferenceConstructive interference occurs when

the wave displacements are in the same direction. The result is a wave

that has an amplitude larger than any of the individual waves. The figure to

the right shows the constructiveinterference of two equal pulses. A

larger pulse appears at point A when the two waves meet. Point A has the largest displacement and is called the

antinode.

Calculating the New Amplitude

Assume left wave to have amplitude of +3 units, and right wave to have -3 units. What is the amplitude of new wave?

Assume left wave to have amplitude of +5 units, and right wave to have -2 units. What is the amplitude of new wave?

Assume left wave to have amplitude of +3 units, and right wave to have +3 units. What is the amplitude of new wave?

0, 6, 3

Standing Waves

are created by continuous interference.

There is a name for these things:

There are calculations for these things:

RefractionThe change in the direction of waves at the boundary between two different media is known as refraction. It is caused by the wave changing speeds as it enters a different medium.

Bends which direction?If the wave slows down in the new medium, it will bend toward the normal. If the wave speeds up in the new medium, it will bend away from the normal.

FST = Fast to Slow, Towards Normal

SFA = Slow to Fast, Away From Normal

Diffraction

Polarization….what does that mean?

A light wave that is vibrating in more than one plane is referred to as unpolarized light. Light emitted by the sun, by a lamp in the classroom, or by a candle flame is unpolarized light. Such light waves are created by electric charges that vibrate in a variety of directions, thus creating an electromagnetic wave that vibrates in a variety of directions. This concept of unpolarized light is rather difficult to visualize. In general, it is helpful to picture unpolarized light as a wave that has an average of half its vibrations in a horizontal plane and half of its vibrations in a vertical plane.It is possible to transform unpolarized light into polarized light. Polarized light waves are light waves in which the vibrations occur in a single plane. The process of transforming unpolarized light into polarized light is known as polarization. There are a variety of methods of polarizing light.

For more info, check out http://www.physicsclassroom.com/class/light/Lesson-1/Polarization

Comparison between waves

Is there anything that may need to be clarified in this question?