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Transcript
The Energy of Waves Waves General and Electromagnetic Nature of Waves Waves are disturbances that transfer energy from place to place. Energy can be carried away from its source by a wave, but the medium does not move with the energy. Wave Travel As waves move through media (such as a solid, liquid or gases) it performs work by transferring energy from one particle (atom) to another. Sound waves transfer energy by vibration of particles in a medium. Sound Waves Require a medium to travel – they vibrate particles. Waves that require a medium are called mechanical waves. Space is not a media (void of Matter)– therefore we cannot hear the explosion of a super nova – we can only see it. Electromagnetic Waves An Electromagnetic Wave is a wave that can travel through empty space or matter and is produced by charged particles that are in motion. Forces All Matter (Atoms - Protons & Electrons) exert positive and negative charges creating an Electrical Field. Thus - this Electric Field (E) exerts a force on all other charged particles that are in a field. Forces The electromagnetic wave is made of two parts—an electric field and a magnetic field. These fields are force fields. A force field enables an object to exert forces on other objects, even though they are not touching. Forces - Magnetic Just as gravitational field exerts a force on a mass, a magnetic field exerts a force on another magnet and on magnetic materials. Magnetic fields cause other magnets to line up along the direction of the magnetic field Earthquakes 3 Types of Mechanical Waves Primary waves (P Waves) Cause particles in rocks to move back and forth in the same direction that the wave is traveling. 3 Types of Mechanical Waves Secondary Waves (S – Waves) Causes particles in rocks to move at right angles to the direction of the wave travel. 3 Types of Mechanical Waves Surface Waves Causes rock particles in a backward, rolling motion and side-to-side, swaying motion. Waves Waves carry energy & information WAVES DO NOT CARRY THE MEDIUM!!! Wave Energy can provide information such as: Sound Color Pictures Radio waves – tv Microwave – cell phones Wavelength ( )Lambda: The length of one complete cycle of a wave is from crest to crest or trough to trough. Amplitude How high the wave rises above, or falls below, the normal level is called the wave’s amplitude. The amplitude of a transverse wave is onehalf the distance between a crest and a trough Higher the wave – the greater the energy. Frequency How many waves pass in 1 sec. The faster the vibration is, the higher the frequency is of the wave that is produced. Measured Unit in hertz (Hz) How fast the wave can transfer energy. How fast the wave can transfer energy. v=fx v = speed (velocity) Units=m/s f = frequency Units=Hz = wavelength Units=m Wave Speed Longitudinal Waves Also called Compressional Waves requires a Media Wave and energy are in same direction Ex: Slinky The compression will move along the slinky forward and then back. Sound Longitudinal Wave Parts Compression-The condensed portion Rarefaction-The separated part of the wave. Wavelength-distance from compression to compression Do not require a Medium Visible Light does not require media. They are Electromagnetic Waves. Examples: microwaves, X-Rays, TV and radio waves. Natural Waves: Even though electromagnetic waves do not require a media they can travel through space, air, water, and glass. Electromagnetic Waves Sun light travels through space, air and water to warm our planet and sustain life. Electromagnetic waves travels fastest through space. the speed of light = 299 792 458 m / s usually stated as 300, 000 km/s or 983,571,056 feet per second Electromagnetic Waves Waves in the electromagnetic spectrum vary in size from very long radio waves the size of buildings, to very short gamma-rays smaller than the size of the nucleus of an atom. Electromagnetic Wave All electromagnetic radiation has fundamental properties and behaves in predictable ways according to the basics of wave theory. Electromagnetic radiation consists of an electrical field (E) which varies in magnitude in a direction perpendicular to the direction in which the radiation is traveling, and a magnetic field (M) oriented at right angles to the electrical field. Both fields travel at the speed of light (c). Electromagnetic Radiation Transverse Waves Wave and energy move perpendicular to each other. (90 degrees) The wave travels to the right as the oscillation points move up and down. Transverse Waves Energy moves left to right as waves moves up & down Ex: water waves A Rope that is moved up and down Light Transverse Waves TRANSVERSE WAVES!!!! All travel at the same speed The difference is in the frequency and the wavelength. If one goes up, the other goes down. Parts of A Transverse Wave Crests: high point of the wave Troughs: low point of the wave Parts of the EM Spectrum Radio WavesLongest wavelength, lowest energy, lowest frequency. Used for TV’s, Radios and Cell Phones Example: Radio Waves - Echolocation Radar: RAdio Detecting and Ranging Radar first used In WWII Echolocation is used by bats, dolphins and many whales Microwaves A form of radio waves-some books place them separately and some put them in with radio. They are the highest frequency (most energy) of the radio waves. Infrared (IR) Heat Used to find people in the woods. Infrared film detects how hot something is. Used to detect cancer Beneath red Visible Light ROY G. BIV-colors of visible light. Sunlight emits UV along with other rays. Vitamin D Too much harmful. Mostly filtered by ozone. Red is longest wavelength Visible Light Ultraviolet Radiation Main source is sunlight Helps your body produce vitamin D Overexposure = burns and skin cancer Sunscreen helps to block Beyond violet X-rays and Gamma Rays X-rays-See bones. High Energy Use lead to block! Gamma rays-highest energy Used to treat cancer Generated by radioactive atoms Wave Interactions Interaction -Waves run into other objects or another wave Interaction can increase or decrease wave energy Interaction can change the properties of the wave Interaction can change the direction Reflection A wave bouncing off of a surface Mirror Wave hitting a wall Incident wave – moving to surface Reflected wave – moving away from surface Reflection Reflection Refraction Bending of wave as it changes speed Speed changes from on medium to another Air to water Water to oil Refraction Refraction Diffraction Bending of a wave when it comes into contact with the edge of another object Light bending around a door Diffraction – Sound Waves Interference The result of two or more waves overlapping each other. When sound waves from several instruments combine the wave produces a higher amplitude thus a louder sound Interference The effect of 2 or more waves interacting Can be constructive or destructive Constructive Interference Wave crest come together at the same location. Waves join together to make a larger wave. Constructive Waves Increased Amplitude Destructive Interference The crest of one wave meets the trough of another wave Crest and trough subtract from each other to make a smaller wave Sometimes the interference cancels both waves Destructive Wave Decreased Amplitude Standing Wave Is a wave that forms a stationary pattern in which portions of the wave are at the rest position due to total destructive interference and other portions have a large amplitude due to constructive interference. Standing Wave Resonance All objects have a frequency or set of frequencies with which they naturally resonate when struck, plucked, strummed or somehow disturbed. Each of the natural frequencies at which an object vibrates is associated with a standing wave pattern. When an object is forced into resonance vibrations at one of its natural frequencies, it vibrates in a manner such that a standing wave is formed within the object. So the natural frequencies of an object are merely the harmonic frequencies at which standing wave patterns are established within the object. Resonance Doppler Sound Change in frequency and pitch of a sound that is caused by either the movement of the source or the listener Ambulance Race car Effect