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# Sound and Waves Introduction - PowerPoint PPT Presentation

Sound and Waves Introduction. Physical Science. Mechanical Wave. Mechanical waves require a medium Examples: shaking a rope or string, ocean tides, slinky and spring, diffusion of heat, etc. Waves carry energy from one location to another. Types of Mechanical Waves. Three types

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### Sound and Waves Introduction

Physical Science

• Mechanical waves require a medium

• Examples: shaking a rope or string, ocean tides, slinky and spring, diffusion of heat, etc.

• Waves carry energy from one location to another

• Three types

• Transverse Waves

• Longitudinal Waves

• Surface Waves

• Particles vibrate perpendicular of the direction the wave travels.

• Trough is the lowest point and crest is the highest point.

• Examples: A shaken string; electromagnetic radiation, radio waves, cell phone signals; AC current; etc.

• Particles vibrate in the direction of propagation!

• Experiences compression: the area where the particles are most close together and rarefaction: the area where the particles are most distance from one another.

• Examples: Sound waves, can be made on slinky, air cannons, etc.

• A surface wave travels along a surface that separates two medium.

• Period (T) – The time required to complete one cycle for a wave. Units are in seconds.

• Frequency (f) – The number of complete cycles in a give time. Units of f are in Hertz (Hz). AKA inverse seconds 1/s

• This means T=1/f and f=1/T

• Wavelength (λ) is the distance between crest or toughs for transverse waves and the distance between compressions or rarefactions for longitudinal.

• Lambda is how your pronounce λ

• Wave length units are meters

• Wave speed is equal to wave length times frequency that is V= λ x f

• or if you hate λwave speed = frequency x wave length

• Wave speed has units of meters per second (m/s)

• The speed of light is always c however!

• This is how “big” the wave is or rather how large the displacement of the wave is from the origin.

• So very many properties.

• Reflection, Refraction, diffraction, interference, standing waves

• Reflection occurs when a wave bounces off a surface/barrier it is on able to pass through.

• The speed and frequency of the wave does not change during a reflection.

• Refraction occurs when the wave enters a new medium at an angle and changes direction.

• Wave speed does change upon entering a new medium

• This is how rainbows are created and how ocean waves change direction.

• Diffraction is the bending of a wave through or around an obstacle.

• This is an important property of light and is often used in quantum mechanics.

• This is an extremely important property of waves!

• There are two types: constructive and destructive

• Constructive and destructive interference are both examples of the superposition.

• Superposition is how sound canceling headphones work, amplifiers, musical instruments (via the formation of standing waves

• There is no music without superposition!

• Two like waves combine to have there amplitudes add forming an over all larger amplitude wave.

• For sound, this makes the sound louder!

• Two waves combine to make a smaller amplitude wave.

• This makes sound more quite and is how sound canceling head phones work!

• Standing waves only form if multiple half of wavelengths fit into the length of a vibrating cord or string.

• They have nodes and antinodes

• Nodes are at a location of zero displacement

• Antinodes are at the highest points of the wave

• Sound, is again, a longitudinal wave!

• Sound travels at about 343 m/s at room temperature

• The louder a sound is the higher its intensity

• Larger intensities mean higher decibels

• A rock concert is often at the threshold of pain and you will lose hearing with out protection

• A pitch is the frequency of sound as you perceive it.

• High frequencies yield a high pitch and low frequencies a low pitch

• Middle C has a frequency of 261 Hz, while an F# has a frequency of about 370 Hz. Well for first harmonics anyways.

• The Doppler effect is the change in frequency of a sound caused by the motion of the listener and/or source.

• This effect also affects light from distance stars and is known as red/blue shifted light.

• AKA light and much more!

• Electromagnetic waves are created from accelerating electrons.

• Electromagnetic waves can travel through a vacuum and matter. This means an electromagnetic wave require no medium to travel!

• All electromagnetic waves travel at c, the speed of light in a vacuum.

• Also, Electromagnetic is often abbreviated as EM.

• Electromagnetic waves can vary in wavelength and frequency

• Again v = f x λ

• However, v = c for EM waves unless otherwise stated.

• EM waves behave very peculiar, they behave both like waves and particles.

• This is known as wave particle duality and was discovered by Albert Einstein during his studying of the photoelectric effect.

• EM energy is carried by little particles called photons and a photons energy is dependent on a waves frequency.

• EM waves come in all sorts of variety and are not just limited to visible light.

• Includes both FM (frequency modulated) and AM (amplitude modulated) wavelength

• Also includes: TV’s

• Includes microwaves (hopefully obviously)

• Microwaves work by hitting the dipole moments in fats and water stored in food producing thermal energy

• Infrared is the wave length of light are bodies give off and most objects produce.

• Infrared light is also used in TV remotes

• Some infrared light can be seen by your cell phones camera!

• This is the ROY G. BIV we see from a rainbow and is the light we can see.

• This is the invisible light produced by the sun responsible for sun burns!

• It can kill a large amount of germs and bacteria and is often used for medical sterilization

• X rays have very short wave lengths and have a high energy

• They can penetrate a large amount of matter and are often used in medical applications

• The highest frequency waves possible.

• These waves can slice through cell membranes and damage your DNA possibly causing cancer

• It is also used to treat cancer however, by destroying the cancer cells!

• If theres time