Waves

• A wave is a repeating disturbance or movement that transfers energy through matter or space. • There are two type of Main types waves based on what they can travel through : 1. Mechanical Waves – Require a medium to travel through. Example: Sound Waves 2. Electromagnetic Waves – Do not require a medium to travel through Example : Light Waves

Types of Waves • Longitudinal wave oscillations are in the direction of motion (parallel to the motion) • Transverse Wave oscillations are perpendicular to the direction of Motion

Physical Examples • Longitudinal wave Travel parallel to the direction of the wave movement • sound waves • earthquake P-waves • Transverse Wave Travel perpendicular to the direction of the wave movement • water waves • • earthquake S-waves light waves

Wave Parameters Wavelength ( l ) length or size of one oscillation Amplitude (A) strength of disturbance (intensity) Frequency (f) repetition / how often they occur per second

Wave Properties Waves are oscillations and they transport energy.

The energy of a wave is proportional to its frequency.

Fast oscillation = high frequency = high energy Slow oscillation = low frequency = low energy The amplitude is a measure of the wave intensity.

SOUND: amplitude corresponds to loudness LIGHT: amplitude corresponds to brightness

• What is the Wave length?

Measure from any identical two successive points

5 10 15 20 25 30 35 40

(nm)

• What is the Wave length?

Measure from any identical two successive points

5 10 15 20 25 30 35 40

(nm) 30nm – 10nm = 20nm

• What is the Wave length?

Measure from any identical two successive points • • There are 4 complete oscillations depicted here ONE WAVE = 1 COMPLETE OSCILLATION

5 10 15 20 25 30 35 40

(nm) 22.5nm - 2.5nm = 20nm

• Frequency Frequency = number of WAVES passing a stationary point per second (Hertz)

Frequency and Period Frequency (f) = number of waves per a second Period (T) = the time it takes for one wave T = 1/f f = 1/T If a source is oscillating with a period of 0.1 seconds, what is the frequency?

f = 1/(0.1) = 10 Hz It will complete 10 oscillations in one second. (10 Hz) If a source oscillates every 5 seconds, its period is 5 seconds, and then the frequency is…????

• f = 1/5 = 0.2 Hz.

Wave speed depends on the wavelength and frequency.

wave speed v =

l

f

Wave Speed v = l f Which animal can hear a shorter wavelength?

Cats (70,000 Hertz) or Bats (120,000 Hertz) l = v/f Higher frequency = shorter wavelength Lower frequency = longer wavelength

Doppler Effect • • Change in frequency of a wave due to relative motion between source and observer.

A sound wave frequency change is noticed as a change in pitch.

Doppler Effect for Light Waves • Change in frequency of a wave due to relative motion between source and observer.

A light wave change in frequency is noticed as a change in “color”.

When an object: Moves away : frequency is decreased = redshift Moves toward : Frequency is increased = blue shift

Constructive Interference • Waves combine without any phase difference • When they oscillate together (“in phase”)

Wave Addition Amplitude ~ Intensity

Destructive Interference • Waves combine differing by multiples of 1/2 wavelength • They oscillate “out-of-phase”

Wave Subtraction

The Behavior of Waves

• Waves can either be absorbed, reflected, refracted, and diffracted.

• When a wave is absorbed the energy is absorbed by the object that was hit by the wave.

Reflection

• Reflection occurs when a wave strikes an object or surface and bounces off, therefore changing its direction. • The angle of incidence =angle of reflection

B. Refraction

•

Refraction

• bending of waves when passing from one medium to another • caused by a change in speed • slower (more dense)  light bends toward the normal SLOWER FASTER • faster (less dense)  light bends away from the normal

B. Refraction

•

Refraction depends on…

• speed of light in the medium, which depends on the density of the medium. The MORE dense the medium the slower light will travel. • wavelength of the light - shorter wavelengths (blue) bend more

Snell’s Law

n 1 sinϴ 1 =n 2 sinϴ 2 n= the refractive index of the material the light is traveling in. n=c/v c= 3x10 8 m/s

Diffraction

• Diffraction is the bending of waves around a barrier. • Longer wavelengths will bend more. • Think about it like moving a small object around a corner and a large object around a corner, which has to bend more??

Dual Particle Duality

There are two theories on what light is made out of because of the way it acts because it acts both like a wave and matter. What scientists have determined is that light travels like both waves and packets of energy and matter called photons.

Ray Diagrams

The Electromagnetic Spectrum

•

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 • electric and magnetic components are perpendicular

The Electromagnetic (EM) Spectrum

long l low

f

low energy short l high

f

high energy

Types of EM Radiation

• LOW Energy • • Long Wavelength Low Freq High Energy Short Wavelength High Freq • Rabbits Meet • Radio In Very Unusual Xciting Gardens Micro Infared Visible • ROYGBV UV X-Ray Gamma

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

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.