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 3rd 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. Characteristics1. Frequency:

a. Complete = orb. Symbol: fc. 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

s1

2. Period:

a. Symbol: Tb. Units: seconds (s)c. Equation:

Time required for one complete wave cycle to pass a point

fT 1

Note:

Tf 1

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: Ab. 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: vc. Equation: d. Units:

Distance that one point on a wave will move per unit time

fv

fv )(1 ms

e. Speed of all electromagnetic waves is the same

Light Speed! (c) = 3.00 x 108 m/s

f. Speed of sound waves on Earth at sea level = 3.31 x 102 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 boomConstantly 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 1014 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 #28 12/13

An electromagnetic wave travels along with a wavelength of 6.12 x 10-7 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 10-7 m?

B. Periodic Wave Phenomena1. 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

wavelengthb. 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

21

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 wavesOccurs 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”Interferenc

e

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 __________. decrease

s

Light Diffracts Too!

Journal #29 12/16 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

fv becomes cf or

fc

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 Diagrams1. Arrows can be drawn perpendicular to wave fronts indicating direction of movement

2. Incident Ray:

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: θi

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

ri

3. Law of Reflection applies to any shape barrier

D. Reflection from Mirrors1. Plane Mirrors

a. form virtual images appear “inside” the

mirror can’t be projected on a

screenb. all light rays follow the law of

reflection

2. Concave Mirrorsa. 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 focus are real, inverted and magnified

e. objects between focus and mirror are virtual and magnified

3. Convex Mirrorsa. 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

decrease

remain the sameTOWARD 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

increase

remain the sameAWAY 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: nc. 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 increase

s

F. Refraction through Lenses1. Image on same side of lens as object = Virtual2. Image on opposite side of lens as object = Real3. 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 #30 12/18

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 ________________.