Waves
A wave is a disturbance that transfers energy without the large-scale transfer of matter!!
Well Bill, that would be Mechanical and Electromagnetic!! Hope he doesn’t make me spell them!! There are 2 types of waves!! Can you name them? Well Bill, that would be Mechanical and Electromagnetic!!
Do you know the 2 ways waves propagate? Waves are either transverse(think Perpendicular) or longitudinal(think Parallel)!!
Wave Characteristics(Review)
Wave Characteristics(Review)
Wave Characteristics(Review) Frequency--# waves per unit time
Relationship between frequency and period Frequency= # waves per time. Period= time per wave. They are the inverse of each other. If you know one and want to know the other, simply take the reciprocal. Ex. Frequency = 2 Hz Period = ½ or .5 s
Wave Characteristics(Review) Wave velocity—how fast a wave travels Remember:
Guess no one around here knows anything about the Doppler effect!! Where have you heard of the Doppler effect?? Or just the word Doppler?
Doppler Effect Apparent change in frequency(pitch) occurs because of the waves either “squishing” together(shorter wavelengths) or spreading apart(longer wavelengths). The velocity of the sound wave doesn’t change, so if the wavelength changes, the frequency must also.
Train sitting still sounding its whistle!!!
Train moving toward the right, while sounding its whistle!!
Wave Properties Reflection—bouncing back of a wave as it hits a reflective surface. Refraction—bending of a wave as it moves from one substance to another. Diffraction—Bending(spreading) of a wave moving through the same substance(around a corner) Interference—combining of 2 or more waves as they pass “through” each other.
Reflection
Reflection Law of Reflection—the angle of incidence is equal to the angle of reflection.
Watch some hammers reflect off the beam in the ceiling!!! Click on the hammer!
Refraction
Refraction Before you look further into refraction, I would re-examine the data we have on wave velocity and the things that affect wave velocity!!
Remember the two types of waves: Today let’s consider how the density of a medium affects the velocity of a wave through that medium!! Remember the two types of waves: Mechanical—must have something to travel through. Electromagnetic—can travel through empty space.
Wave Velocity Mechanical Waves Electromagnetic Waves Tap your finger on your desk. Now put your ear down on the desk and continue gently tapping your finger. Your finger should stay about the same distance away from your ear as it was when you tapped the first time. How is the noise different? Consider the picture of a person running through an empty field!!! How fast can she run? Consider the picture of a person running through the woods!! What happens to his speed as he runs into and then out of the woods?
Nothing in the way to slow her down!! Click to go back Nothing in the way to slow her down!!
There are trees in the way. This person has to slow down, so as not to hit the trees.
Wave Velocity Mechanical waves have to have a medium. Electromagnetic Waves Mechanical waves have to have a medium. The denser the medium, the better they travel!! Increase density= increase velocity Electromagnetic waves can travel best through empty space. The denser the medium, the slower they travel. “Will discuss more later!!”
Refraction Waves refract(bend) as they move from one substance to another, because the speed of the wave changes. The speed changes because the density of the medium changes. “Remember wave velocity through various media!!”
Consider a band walking in formation. Band moves from pavement to mud Consider a band walking in formation!! Band moves from pavement to mud!!! What happens to the entire formation!!
Original path New path
Less dense to more dense More dense to less dense Direction of refraction depends on what the wave is moving from and what the wave is moving into!! Less dense to more dense More dense to less dense More to less bends away from the normal. Remember MLA citation Less to more bends toward the normal.
Which is more dense? The white area, or the gray area.
Which is more dense? The white area, or the blue area.
Stop p. 295 Q’s 1-6 p. 299 Q’s 1-3 p. 301 Q’s 1-7 Turn in!!
Wave Properties Reflection—bouncing back of a wave as it hits a reflective surface. Refraction—bending of a wave as it moves from one substance to another. Diffraction—Bending(spreading) of a wave moving through the same substance(around a corner) Interference—combining of 2 or more waves as they pass “through” each other.
Diffraction Bending(spreading) of a wave traveling through the same substance(around a corner). Click
Interference 2 or more waves combining to form a new wave. What happens when 2 waves “crash” into each other? Remember the coolest wave ever seen??? What do waves do? They carry energy! Remember Amplitude corresponds with energy!!!
Notice the 2 amplitudes: One shows a positive amplitude and the other shows a negative amplitude. This is crucial to your understanding of wave interference.
2 types of interference Constructive Interference Destructive Interference Waves “add together” because they are in “phase” with one another. Waves “cancel” because they are out of “phase” with each other.
Green Line—represents wave #1 Blue Line –represents wave #2 Black line—Combination of wave #1 and wave #2
What type of interference is shown? Red--Wave #1 Blue--Wave #2 Green—Wave #1 + Wave #2
What type of interference is shown? Red--Wave #1 Blue--Wave #2 Green—Wave #1 + Wave #2
What type of interference is shown? Red--Wave #1 Blue--Wave #2 Green—Wave #1 + Wave #2
What type of interference is shown? Red--Wave #1 Blue--Wave #2 Green—Wave #1 + Wave #2
Electromagnetic Spectrum
Electromagnetic Spectrum The spectrum is on your formula sheet. Wavelength is shown. Must be able to answer questions about frequency and amount of energy, also. If all electromagnetic waves travel at the speed of light, remember the relationship between wave velocity, frequency, and wavelength. As the wavelength get longer, the frequency and amount of energy gets smaller. As the wavelength gets shorter, the frequency and amount of energy gets higher.
What waves have the longest wavelength? What waves have the shortest wavelength?
What waves have the highest frequency? What waves have the lowest frequency?
What waves carry the most energy? What waves carry the least energy?