Waves, Sound, Light and the Electromagnetic Spectrum Notes

Wave Mechanical wave Medium Transverse wave Longitudinal wave Crest Trough Compression Rarefaction Wavelength Frequency Amplitude Wave speed formulas Reflection Refraction Sound Speed of sound Decibels Doppler effect Electromagnetic wave Electromagnetic spectrum Radio waves Infrared rays Visible light Ultraviolet rays X – rays Gamma & cosmic rays Color White light Laser Optical fibers Total internal reflection Vocabulary

A wave is a disturbance that transfers energy through matter or through space. Some kinds of waves move through a medium that may be solid, liquid, or gas. These waves are called mechanical waves. Light waves (and other electromagnetic waves) are unique in that they don’t require a medium. Waves

Medium – the matter through which a mechanical wave travels What causes waves?  Mechanical waves are produced when a source of energy causes a medium to vibrate.  Vibration - a back and forth or up and down motion. Waves

Two kinds of mechanical waves Transverse waves - waves that move the medium at right angles to the direction in which the waves travel. Like: Slinky waves Water waves Longitudinal waves – waves that move the medium parallel to the direction in which the waves travel. Like: Sound waves Some earthquake waves and Slinky waves

Transverse Waves The highest point on a transverse waves is called a crest while the lowest point if called a trough.

In longitudinal waves, the part where particles are closest together are called compressions while rarefactions are the places where particle are farthest apart. Longitudinal Waves

Wavelength is the distance between two corresponding (same) parts of a wave. Notice the wavelength of the: Wavelength Longitudinal wave Transverse wave

Frequency is the number of waves that pass a given point in a certain amount of time. Wave Frequency Transverse wavesLongitudinal waves

The amplitude of a wave is the maximum distance that the particles of the medium carrying the wave move away from their rest positions. Amplitude Transverse waves Longitudinal waves

The speed, wavelength, and frequency of a wave are related to one another by a mathematical formula: Speed = Wavelength X Frequency OR Frequency = Speed / Wavelength Wavelength = Speed / Frequency Wave Speed S WF

A reflection occurs when an object or a wave hits a surface through which it cannot pass, and it bounces back. Reflection Flat Surfaces Curved surfaces

Refraction occurs when a wave enters a new medium at an angle and one side of the wave changes speed before the other side, causing the wave to bend. Refraction

Sound is a disturbance that travels through a medium as a longitudinal wave. You can compare sound waves to slinky compression waves: Sound Waves

Although sound waves are longitudinal waves, we can compare them to transverse waves. In sound waves, the compressions compare to crests while the rarefactions compare to troughs. The amplitude is simply how compressed the particles of the medium are at the compressions.

The speed of sound depends upon the elasticity, density, and temperature of the medium the sound travels through. Greater elasticity – Sound is faster Greater density – Sound is slower Higher temperature – Sound is faster Speed of Sound

The loudness of different sounds is measured in units called decibels. However, pitch depends on the frequency of the sound wave. Measuring Sound

The Doppler Effect is the change in frequency of a wave as its source moves in relation to the observer. For example, when a police car with its siren on is coming toward you, the frequency seems higher, but when it passes and moves away it seems lower. The Doppler Effect

The Electromagnetic Spectrum

An electromagnetic wave consists of vibrating electric and magnetic fields that move through space at the speed of light. Electromagnetic waves are produced by the interactions of charged particles. Think of how magnets interact with each other – these are interactions between charged particles. Electromagnetic Wave

The electromagnetic spectrum consists of many types of electromagnetic waves that all move at the speed of light, but have different wavelengths and frequencies. Electromagnetic Spectrum

Radio waves are the electromagnetic waves with the longest wavelengths and the lowest frequencies. They include broadcast waves (for radio and television) and microwaves. Radio Waves

Infrared rays have more energy than radio waves and are often called heat rays. Lamps that give off infrared rays can keep food warm or warm up a cold room. Infrared Rays

Electromagnetic waves that you can see are called visible light. They make up a small part of the electromagnetic spectrum, but include all the colors you see. White light contains all colors. Visible Light

Ultraviolet rays have shorter wavelengths and higher frequencies than visible light, so they have more energy as well. In fact, they are used to kill bacteria on hospital equipment and foods. Ultraviolet Rays

X-rays have higher frequencies and shorter wavelengths than ultraviolet rays. Since they have more energy, they are able to penetrate most matter. We use x-rays to view broken bones or teeth. X-Rays

Gamma and Cosmic rays have the shortest wavelengths and the highest frequencies. Because of this they are the most penetrating of all electromagnetic waves. Gamma and Cosmic Rays

When light strikes an object, the light can be reflected, transmitted, or absorbed. The color of an object is the color of light it reflects. The shirt reflects red Because it is red. The Shorts reflect blue Because they are blue. Light and Color

When you shine white light (the light that includes all the visible colors) on a colored object, the object will appear to be the color of the light it reflects. All the other visible colors are absorbed. If the object reflects a warm color (red, orange, yellow) it will be cooler than an object which absorbs them. For example, if you shine light on a blue object, it will absorb the warm red light, and will be warmer than a red object which would reflect that light. Light and Color

LASER – Light Amplification by the Stimulated Emission of Radiation. A laser is a device that Produces a narrow beam of coherent light. In other words, laser light consists of light waves that all have The same wavelength, or color. The waves are coherent, or in step. Lasers

Lasers have many uses: Bar code readersLaser surgery Precision cuttingLaser Tag!! Lasers

Optical Fibers (fiber optics) are long thin strands of glass or plastic that can carry light for long distances without allowing the light to escape. Fiber Optic Cables

Optical fibers can carry a laser beam for long distances because the beam stays totally inside the fiber as it travels. This happens because the laser light has a large angle of incidence – total internal reflection. Fiber Optics