Waves-Unit 5

Doppler Effect

A change in sound frequency caused by motion of the sound source, motion of the listener, or both. Discovered by Austrian scientist Christian Doppler.

Mechanical Waves

One of 3 main types of waves, transverse, longitudinal and surface, made up of vibrating particles in a solid, liquid and gas. Example include water waves and sound waves.

How are waves measured?

A wave is measured by its frequency, wavelength and amplitude.

Longitudinal

All mechanical waves can be described as either transverse, longitudinal and surface, depending on the direction of their vibrations. In longitudinal waves, the particles vibrate in the same direction as the wave is traveling. Sound waves are longitudinal waves.

Transverse

All mechanical waves can be described as either transverse, longitudinal or surface, depending on the direction of their vibrations. Transverse waves are waves in which the particles vibrate at right angles to the direction the wave is traveling. Water waves are transverse waves.

Surface

All mechanical waves can be described as either transverse, longitudinal or surface. Surface wave is a wave that travels along a surface separating two media. An example of a surface wave is a ocean wave.

Draw Electromagnetic Spectrum With Wave Types

Electromagnetic waves are a form of energy waves that have both an electric and magnetic field. Electromagnetic waves are different from mechanical waves in that they can transmit energy and travel through a vacuum. Electromagnetic waves are classified according to their frequency. The different types of waves have different uses and functions in our everyday lives. The most important of these is visible light, which enables us to see. Radio Waves Radio waves have the longest wavelengths of all the electromagnetic waves. They range from around a foot long to several miles long. Radio waves are often used to transmit data and have been used for all sorts of applications including radio, satellites, radar, and computer networks. Microwaves Microwaves are shorter than radio waves with wavelengths measured in centimeters. We use microwaves to cook food, transmit information, and in radar that helps to predict the weather. Microwaves are useful in communication because they can penetrate clouds, smoke, and light rain. The universe is filled with cosmic microwave background radiation that scientists believe are clues to the origin of the universe they call the Big Bang. Infrared Between microwaves and visible light are infrared waves. Infrared waves are sometimes classified as "near" infrared and "far" infrared. Near infrared waves are the waves that are closer to visible light in wavelength. These are the infrared waves that are used in your TV remote to change channels. Far infrared waves are further away from visible light in wavelength. Far infrared waves are thermal and give off heat. Anything that gives off heat radiates infrared waves. This includes the human body! Visible light The visible light spectrum covers the wavelengths that can be seen by the human eye. This is the range of wavelengths from 390 to 700 nm which corresponds to the frequencies 430-790 THz. You can go here to learn more about the visible spectrum. Ultraviolet Ultraviolet waves have the next shortest wavelength after visible light. It is ultraviolet rays from the Sun that cause sunburns. We are protected from the Sun's ultraviolet rays by the ozone layer. Some insects, such as bumblebees, can see ultraviolet light. Ultraviolet light is used by powerful telescopes like the Hubble Space Telescope to see far away stars. X-rays X-rays have even shorter wavelengths than ultraviolet rays. At this point in the electromagnetic spectrum, scientists begin to think of these rays more as particles than waves. X-rays were discovered by German scientist Wilhelm Roentgen. They can penetrate soft tissue like skin and muscle and are used to take X-ray pictures of bones in medicine. Gamma rays As the wavelengths of electromagnetic waves get shorter, their energy increases. Gamma rays are the shortest waves in the spectrum and, as a result, have the most energy. Gamma rays are sometimes used in treating cancer and in taking detailed images for diagnostic medicine. Gamma rays are produced in high energy nuclear explosions and supernovas.

Speed

How fast a wave travels can be calculated using this formula: Speed= Wavelength x Frequency Example: One end of a rope is vibrated to produce a wave with a wavelength of 0.25 meters. The frequency of the wave is 3.0 hertz. What is the speed of the wave? Answer: Speed = .25m x 3.0 Hz = .75 m/s

Interference

If two or more waves meet they have an effect on each other called Interference. There are 2 different kinds of interference and depends on which parts of the waves coincide.

Primary Wave

P waves, also called compressional waves or primary waves, move through material by squeezing and stretching the material in the same direction as the wave is moving. S waves, also called shear waves or secondary waves, move materials at right angles to the wave direction.

Photon

Packets of electromagnetic energy. The greater the frequency of an electromagnetic wave, the more energy each of its photons has.

Secondary Wave

S waves, also called shear waves or secondary waves, move materials at right angles to the wave direction.

Wavelength

The distance between a point on one wave and the same point on the next, for example, between two troughs.

Pitch

The frequency of a sound as you perceive it. Pitch depends upon a wave's frequency. High frequency sounds have a high pitch and low frequency sounds have a low pitch.

Amplitude

The height from a particle's rest position to a peak. This becomes less as a wave moves away from its source and loses energy. The more energy a wave has, the greater is its amplitude.

Frequency

The number of complete waves that pass a point in one second measured in hertz (Hz).

Use Earthquake Waves to Explain Earth Layers

The structure of Earth's deep interior cannot be studied directly. But geologists use seismic (earthquake) waves to determine the depths of layers of molten and semi-molten material within Earth. Because different types of earthquake waves behave differently when they encounter material in different states (for example, molten, semi-molten, solid), seismic stations established around Earth detect and record the strengths of the different types of waves and the directions from which they came. Geologists use these records to establish the structure of Earth's interior. The two principal types of seismic waves are P-waves (pressure; goes through liquid and solid) and S-waves (shear or secondary; goes only through solid - not through liquid). The travel velocity of these two wave types is not the same (P-waves are faster than S-waves). Thus, if there is an earthquake somewhere, the first waves that arrive are P-waves. In essence, the gap in P-wave and S-wave arrival gives a first estimate of the distance to the earthquake.

Trough

Transverse waves create a regular pattern of high points called peaks and low points below the rest position called troughs.

Crest

Transverse waves create a regular pattern of high points of the wave above the rest position called crests and low points called troughs.

Electromagnetic Waves

Transverse waves made up of continually changing electric and magnetic fields. Like mechanical waves, electromagnetic waves can travel through most solids, liquids and gases. All electromagnetic waves are invisible, except for those that make up light. Examples include light waves and radio waves.

Waves

Waves carry energy.

Destructive Interference

When a peak meets a trough of the same size, they cancel each other out and the wave disappears.

Incident Wave

When a wave hits an obstacle, or passes from one substance (medium) to another, it can change in speed, direction, or shape. Before the change, the wave is called the incident wave.

Reflection

When an incident wave (before any changes happen) hits an obstacle, for example when a water wave hits a sea wall, it bounces back because it cannot pass through. This is called reflection. The wave is reflected back at an angle equal to its angle of approach.

Refraction

When an incident wave enters a new medium it changes speed. It is the bending of a wave as it enters a new medium at an angle because one side of the wave moves more slowly than the other side.

Diffraction

When an incident wave passes through a gap, it spreads out and bends. The smaller the gap compared to the wavelength of the wave, the more it is diffracted.

Constructive Interference

When two peaks of the same amplitude arrive in the same place at the same time, they combine to form a peak twice as large.