Waves & Sound I. Characteristics of Waves Waves Transverse waves Longitudinal waves Measuring waves

A. Waves Waves rhythmic disturbances that carry energy through matter or space Medium material through which a wave transfers energy solid, liquid, gas, or combination electromagnetic waves don’t need a medium (e.g. visible light)

B. Waves & Energy Waves Energy Carry energy Waves carry energy Waves are caused by vibrations Can do work Move objects Energy Waves carry energy Vibration is a transfer of energy As waves carry energy the particles in the medium move the direction of the motion determines the type of wave

Electromagnetic Waves C. Categories of Waves Mechanical Waves Must travel through a medium Cannot travel through a vacuum Examples: sound, ocean waves Electromagnetic Waves Does not require a medium Can be transferred through a vacuum Examples: light, UV rays, Visible light

D. Types of Waves Two Types: Longitudinal Transverse

D. Transverse Waves Transverse Waves medium vibrates perpendicular to the direction of wave motion Examples: water waves, electromagnetic waves

corresponds to the amount of energy carried by the wave B. Transverse Waves Wave Vocabulary corresponds to the amount of energy carried by the wave crests wavelength amplitude nodes troughs

E. Longitudinal Waves Longitudinal Waves (a.k.a. compressional waves) medium moves in the same direction as the wave’s motion Examples: sound waves, springs, slinky

E. Longitudinal Waves Wave Anatomy compression wavelength rarefaction Amount of compression corresponds to amount of energy ≈ AMPLITUDE

F. Measuring Waves Frequency ( f ) # of waves passing a point in 1 second SI unit: Hertz (Hz) 1 second shorter wavelength ⇒ higher frequency ⇒ higher energy

v = λ × f F. Measuring Waves Velocity ( v ) speed of a wave as it moves forward depends on wave type and medium v = λ × f v: velocity (m/s) λ: wavelength (m) f: frequency (Hz)

F. Measuring Waves Solid Liquid Molecules are close together so waves travel very quickly. Molecules are farther apart but can slide past one another so waves do not travel as fast. Gas Molecules are very far apart so a molecule has to travel far before it hits another molecule, so waves travel slowest in gases.

F. Measuring Waves EX: Find the velocity of a wave in a wave pool if its wavelength is 3.2 m and its frequency is 0.60 Hz.

F. Measuring Waves EX: An earthquake produces a wave that has a wavelength of 417 m and travels at 5000 m/s. What is its frequency?

Wave Interactions Wave Interaction When a wave meets an object or another wave. When a wave passes into another medium Examples: reflection, diffraction, refraction, interference, resonance

Reflection Reflection when a wave strikes an object and bounces off Normal Reflection when a wave strikes an object and bounces off incident beam reflected beam

Reflection When a wave bounces off a surface that it cannot pass through

Refraction Refraction bending of waves when passing from one medium to another caused by a change in speed slower ⇒ light bends toward the normal SLOWER FASTER faster ⇒ light bends away from the normal

Refraction The bending of a wave as it enters a new medium at an angle.

Refraction Refraction depends on… speed of light in the medium

Refraction Example: View explanation.

Diffraction The bending of a wave as it moves around an obstacle or passes through a narrow opening.

Diffraction Diffraction bending of waves around a barrier longer wavelengths (red) bend more - opposite of refraction

A. Speed of Sound 344 m/s in air at 20°C Depends on: Type of medium travels better through solids than through liquids can’t travel through a vacuum Temperature of medium travels faster at higher temperatures

converted to nerve impulses in cochlea B. Human Hearing sound wave vibrates ear drum amplified by bones converted to nerve impulses in cochlea

B. Human Hearing Pitch highness or lowness of a sound depends on frequency of sound wave human range: 20 - 20,000 Hz ultrasonic waves subsonic waves

B. Human Hearing Intensity volume of sound depends on energy (amplitude) of sound wave measured in decibels (dB)

B. Human Hearing DECIBEL SCALE 120 110 100 80 70 40 18 10

A. Electromagnetic Radiation transverse waves produced by the motion of electrically charged particles does not require a medium speed in a vacuum = 300,000 km/s

B. Electromagnetic Spectrum The full range of light

B. Electromagnetic (EM) Spectrum long λ low f low energy short λ high f high energy

C. Types of EM Radiation Rabbits Meet In Very Unusual Xciting Gardens

C. Types of EM Radiation Radio waves Lowest energy EM radiation FM - frequency modulation AM - amplitude modulation Microwaves penetrate food and vibrate water & fat molecules to produce thermal energy

C. Types of EM Radiation Infrared Radiation (IR) slightly lower energy than visible light can raise the thermal energy of objects thermogram - image made by detecting IR radiation

C. Types of EM Radiation Visible Light small part of the spectrum we can see ROY G. BIV - colors in order of increasing energy R O Y G. B I V red orange yellow green blue indigo violet

C. Types of EM Radiation Ultraviolet Radiation (UV) slightly higher energy than visible light Types: UVA - tanning, wrinkles UVB - sunburn, cancer UVC - most harmful, sterilization

C. Types of EM Radiation Ultraviolet Radiation (UV) Ozone layer depletion = UV exposure!

C. Types of EM Radiation X rays higher energy than UV can penetrate soft tissue, but not bones

Radiation treatment using radioactive cobalt-60. C. Types of EM Radiation Gamma rays highest energy on the EM spectrum emitted by radioactive atoms used to kill cancerous cells Radiation treatment using radioactive cobalt-60.