Topic VI.  What is a wave?  How do waves move?  What are the characteristics of waves?  How do waves interact?  How do light waves behave?

I. Introduction to Waves A. Wave: a disturbance produced by a particle vibrating or oscillating about an average position 1. A wave moves through a medium  body of matter or field 2. Mechanical waves: require a material medium  Examples: sound waves & water waves

3. Electromagnetic Waves: produced by changing electric or magnetic field strength at regular intervals  Examples: radio waves, visible light  Can travel through a vacuum

4. Waves transfer ENERGY from the source… NOT mass B. Pulses: a single short disturbance moving through a medium or field

1. When a pulse hits a barrier some of its energy will be…  Reflected: bounced back into medium  Refracted: changes direction/speed  Transmitted: goes through barrier entirely  Absorbed: goes into barrier itself

2. If the barrier is unyielding or more dense, then the pulse will be inverted (Newton’s 3 rd Law) 3. If the barrier is “soft” or movable, the reflected pulse will be similar to the original

C. Types of Wave Motion a. Longitudinal waves require a material medium b. Examples: sound waves, compression waves, P-waves 1. Longitudinal: Vibration parallel to direction the source vibrates…

a. Do not require a material medium b. Examples: electromagnetic waves, S-waves 2. Transverse: Wave vibration is perpendicular to the direction the source vibrates

II. A. Characteristics 1. Frequency: a. Complete =or b. Symbol: f c. Units: # per second ( or s -1 ) = Hertz ( Hz ) d. High frequency = High wave energy Created when the source of a pulse or wave repeats its vibration at regular time intervals Number of complete wave cycles per second

2. Period: a. Symbol: T b. Units: seconds ( s ) c. Equation: Time required for one complete wave cycle to pass a point Note:

Example: Frequency and Period At the beach, you watch the waves come in and a wave crashes every 4 seconds.  What is the period of the wave?  What is the frequency of the wave?  Describe the motion of the water molecules as wave energy travels through.

3. Amplitude: a. Symbol: A b. Units: meters ( m ) Maximum displacement of a particle from equilibrium position

c. Maximum positive displacement is called a crest d. Maximum negative displacement is called a trough

e. For Longitudinal waves, maximum amplitude is related to compression of particles  areas of maximum compression are called condensations  areas of minimum compression are called rarefactions

f. Amplitude is directly related to:  Intensity for light waves (brightness)  Loudness or Volume for sound waves

4. Wavelength: a. Symbol: λ (Greek letter lambda) b. Units: meters ( m ) c. The points used to find wavelength are in phase (360° apart)! The distance between identical points in successive wave cycles

Example: Wave Diagram

5. Wave Speed: a. Related to the wave’s frequency and wavelength b. Symbol: v c. Equation: d. Units: Distance that one point on a wave will move per unit time

e. Speed of all electromagnetic waves is the same Light Speed! ( c ) = 3.00 x 10 8 m/s

f. Speed of sound waves on Earth at sea level = 3.31 x 10 2 m/s = 331 m/s = 762 mph *Remember – sound waves are NOT radio waves!  speed of sound depends on air temperature, density, and altitude

 Breaking the sound barrier…a sonic boom Constantly Trails the object that is moving

Example: Wave Speed, Properties An electromagnetic wave measuring 1 cm from crest to trough travels along and has a frequency of 6.33 x Hz. Which of the two types of waves is this wave? What is the amplitude of the wave in meters? What is the wave’s speed? Calculate the wavelength of the wave. What kind of electromagnetic wave is this? Compare the speed of this wave to the wave generated by a train whistle…

Journal #2812/13 An electromagnetic wave travels along with a wavelength of 6.12 x m. What is the frequency of the wave? (Calculate) What is the period of the wave? Compare the speed of this wave to the speed of sound… and the speed of light. What would the new speed and frequency if the wavelength of the wave changes to 7.5 x m?

B. Periodic Wave Phenomena 1. Wave Fronts:  Example: all points on a crest All parts of a wave cycle that are in phase and moving away from the source

2. Doppler Effect: a. Source approaching an observer:  increased frequency  decreased wavelength b. Source moving away from an observer:  decreased frequency  increased wavelength Stretching or compressing of waves due to movement of the source or receiver Doppler

c. causes changes in pitch in sound waves d. causes changes in color in light waves  Red Shift: source of light moves away from observer (appears more red)  Blue Shift: source of light moves toward observer (appears more blue or violet)

e. Doppler Effect is used in meteorology and law enforcement to better obtain speeds of targets (precipitation and speeders)

Be QUIET…We will be done faster!!

3. Standing Waves: a. Creates:  Nodes: points that do not move  Antinodes: points of maximum amplitude b. Successive nodes or antinodes appear half a wavelength away from each other ( ) Initial and reflected waves appear to be standing still in a given medium

4. Interference: a. Superposition:  superposition principle: add up displacements from individual waves to get the resultant  Example:  Two waves in a medium: Blue = resultant wave Changes to waves occur due to interactions with other waves Occurs when two or more waves travel in the same medium (results in interference) become

b. Constructive Interference: c. Destructive Interference:  Waves combine to form a larger wave  Maximum C.I. occurs when waves are “in phase”  Waves combine to form a smaller wave  Maximum D.I. occurs when waves are “out of phase” Interference

5. Resonance:  the frequency at which a material vibrates is called its natural frequency The natural frequency that a material will vibrate at due to wave exposure

6. Diffraction: a. waves can spread around edges of the barrier b. waves can move through an opening in the barrier – diffracting behind it on both sides The spreading out of waves around a barrier

 As the size of the opening increases the amount of diffraction __________. decreases

Light Diffracts Too!

Journal #2912/16 In the three diagrams below, state the type of interference that will occur between the waves and sketch what the “resultant” wave will look like when the waves pass through each other. (a) (b) (c)

III. A. Visible Light: 1. Given off naturally by Stars, Electricity, and Chemical Reactions 2. Travels at the “speed of light” ( c )  frequency and wavelength of light can be calculated using the formula: Part of the EM-spectrum that can be seen becomes  or

3. Each color has a slightly different frequency 4. Light wave particles vibrate up and down as well as left and right  unpolarized 5. Light can be Polarized:  only one direction of vibration is allowed to pass through a material

6. Complimentary Colors  Produce white or black when placed over each other…  Color Wheel

B. Light Ray Diagrams 1. Arrows can be drawn perpendicular to wave fronts indicating direction of movement 2. Incident Ray: ray Ray that strikes a barrier

3. Normal: 4. Angle of Incidence : Line drawn perpendicular to barrier that a ray strikes Angle to the normal that an incident ray strikes a barrier – Symbol: θ i

Example: Light Ray Diagram

C. Law of Reflection: 1. All angles are measured with respect to the normal line! 2. Symbolic Form: Angle of incidence of a wave equals the angle of reflection

3. Law of Reflection applies to any shape barrier

D. Reflection from Mirrors 1. Plane Mirrors a. form virtual images  appear “inside” the mirror  can’t be projected on a screen b. all light rays follow the law of reflection

2. Concave Mirrors a. can form real images depending on how close the object is to the mirror.  appear “outside” the mirror  CAN be projected on a screen  can be magnified or smaller

b. images form where reflected light rays intersect!

c. objects outside the center of curvature are inverted, real, and smaller

d. objects between center of curvature and focusare real, inverted and magnified e. objects between focus and mirror are virtual and magnified

3. Convex Mirrors a. form virtual images  appear inside mirror  cannot be projected  appear smaller and further than object actually is  large field of view b. used in security & automobiles

E. Refraction of Light 1. If the new medium is more dense…  speed of light will ________________  wavelength will ________________  frequency will ________________  wave will bend ______________________ decrease remain the same TOWARD the normal Changing direction of light rays due to a medium change

More Dense (Water) Less Dense (Air) Normal Refracted Ray Incident Ray Interface

2. If the new medium is less dense  speed of light will ________________  wavelength will ________________  frequency will ________________  wave will bend ______________________ increase remain the same AWAY from the normal

3. Absolute Index of Refraction: a. The A I of R is a ratio of the speed of light in a vacuum ( c ) compared to the speed of light in the material ( v ) b. Symbol: n c. As the index of refraction increases, the density of the substance ___________ and the amount of refraction ___________  How much a material will refract light based on the optical density of the material increases

F. Refraction through Lenses 1. Image on same side of lens as object = Virtual 2. Image on opposite side of lens as object = Real 3. Convex (Converging) Lenses  Can produce real and virtual images  can be magnified or smaller  Ex: magnifying glasses

2. Diverging (Concave) Lenses  Always produce virtual images  Always produce smaller images

Far Sightedness

Near Sightedness

Journal #3012/18 A microwave travels along with a wavelength of 25mm. What is the frequency of the wave? (Calculate) What is the period of the wave? Compare the speed of this wave to the speed of sound… and the speed of light. When this wave encounters a barrier or opening it will _______________. When this wave enters a more dense medium it will ________________.