Warm up
What happens when a wave encounters a boundary at an angle? Draw the results of a wave going from a faster medium to a slower medium (this will help you in today’s game).
Fast
Slow
Warm up
What is light? Is there anything else that is like light? Does anything else travel as fast as light does?
Homework: From memory, list as many as you can of different categories of electromagnetic waves from least harmful to most harmful
Today’s Plan:
Reminders: homework, office hours Wednesday (no office hours Thursday), quiz Friday
Exit Ticket
Exit ticket: What is similar about light, radio waves, and x-rays? What is different? (at least one similarity and one difference)
Earthquakes (p.53)
P-waves and S-waves do different things when they hit liquid...
Refraction Battleship
Set up: Draw a line down the center of the paper, place the container on the middle of the line. Then trace the outline of the container. Lift the container and erase the midline where the container sits, then replace the container. Use a ruler to create the boundary set by the sides of the container.
Refraction Battleship
Take turns setting your battleship and firing.
Setting: place two pins on one side of the board 1cm apart, which represent the ends of your battleship. They must both be on one side (left or right, and both be within the boundary of the container.
Shooting: place two pins on the opposite side (if the ship is on the left, you must shoot from the right). The line formed by the two pins makes the trajectory of your shot.
Most important: both players must look at the pins through the water while the container is lifted. Use a ruler to see if the shot pins line up with the battleship.
One round consists of 3 shots total. (player 1 shoots, then player 2, then player 1 again).
If one player hits more than the other, then they win and the other person is replaced with a new player (the new player chooses who goes first). If both players hit the same number of times, then the person who had only one shot wins and the person who went first is replaced.
Try to line up the pins perfectly, two on each side.
Draw a line from the pins to the container. (do this on both sides
Then remove the box, watching the pins as you lift the container.
Trace the line made by the pins to the boundary of the container on each side, then connect the lines through the boundary of the container.
ϴ
ϴ
Group Data
Incident Refracted
ϴ ϴ
Refraction of light (p.54)- the bending of light as they cross boundaries.
Lenses water Glass
Think-pair-share: So light refracts… what does that tell us about light?
Light might be a wave (the other option is that it is made of particles, more on that later).
If it is a wave, it is different from mechanical waves. Why? What can light travel through that sound (and other mechanical waves) can’t?
Electromagnetic waves (p.49)
Light travels through a vacuum (like space) at a speed of about 299,792,000m/s (about 3x108m/s)
Can light travel through air like sound does?
Yes, but slightly slower - 299,700,000m/s
Electromagnetic waves (p.49)
Light travels through a vacuum (like space) at a speed of about 299,792,000m/s (about 3x108m/s)
Can light travel through air like sound does?
Yes, but slightly slower - 299,700,000m/s
Is there anything else that can travel at these speeds?
Electromagnetic Waves (p.49)
It is important to understand that these are all the same thing. They are the same thing as “light” (a transverse wave of both electric and magnetic fields).
They all travel 300,000,000m/s through space.
The only difference is the frequency.
Question to consider: knowing that they all travel the same speed, which would have a longer wavelength, ones with higher frequency or lower frequency?
Think about it: which would have a higher energy, ones with higher frequency and longer wavelength or lower frequency and shorter wavelength?
Electromagnetic Waves (p.49)
How to remember the EM spectrum:
Roy G Biv
Infrared is just before red and ultraviolet is just past violet. Which one is more harmful?
Radiowaves have the least energy
X-rays and gamma rays have the most
Electromagnetic Waves (p.49)
Think about it: which would have a higher energy, ones with higher frequency and longer wavelength or lower frequency and shorter wavelength?
If the lights are equally bright, then the light with higher frequency would have more energy.
Which would have more energy, a green light or a red light, if they are the same brightness?
Which would have more energy, a really bright red light or a really dim ultraviolet light?
Which would have more energy, a really bright radio wave or a really dim x-ray?
Electromagnetic Waves (p.49)
The energy of a light is dependent on both the intensity (brightness) and frequency of the light.
Have you ever gotten an x-ray before?
Should we be worried about getting an x-ray?
What about UV light? Does this mean we don’t have to worry about UV light?
The harmful effects of EM radiation depend on the intensity, the frequency, and the amount (level of exposure).
Electromagnetic Waves (p.49)
Which ones do cell phones use?
Radio waves
Does this seem likely to give us cancer?
Not so fast...
Electromagnetic Waves (p.49)
Many articles and websites, especially opinion pieces, claim that cell phones do cause cancer.
If someone tells you that cell phones cause cancer, what might you ask them?
If they tell you that there was a massive study that was done that found that radio waves emitted by cell phones caused cancer in rats, what might you do?
Exit Ticket
Exit ticket: What is similar about light, radio waves, and x-rays? What is different? (at least one similarity and one difference)
Plate Tectonics (p.55)
Think-pair-share: What does the theory of plate tectonics tell us? How might it relate to things like volcanos, mountains, and valley?
The Earth’s surface changes slowly over incomprehensibly vast periods of time. As the plates slowly move over the liquid mantle, they can push up against each other...
Plate Tectonics (p.55)
The Earth’s surface changes slowly over incomprehensibly vast periods of time. As the plates slowly move over the liquid mantle, they can push up against each other...
Plate Tectonics (p.55)
Subduction - when one plate slides under another, going back into the mantle.
Mantle - liquid magma
Exit Ticket
Exit ticket: What makes us think that the Earth’s core is liquid? (hint: what happens with different earthquake waves?)
Exit Ticket
Exit ticket: When a wave increases its speed, what happens to its frequency and wavelength?
Earthquake
Early yesterday morning, around 2am, there was a small earthquake that originated somewhere in the bay area.
Sensitive seismographs recorded the movement of the Earth at several locations.
Noise-Canceling Headphones
Noise-canceling headphones utilize interference to effectively nullify (cancel out) sound waves.
How could they do this?
Sound Waves (p.49)
When you increase the volume, the speaker pushes the air harder, so they move a greater distance forward and backward (amplitude).
When the pitch increases, you have more waves each second (frequency)
Amplitude - how far the medium is moved by the wave.
Medium - what the wave is traveling through. (plural - media)
Frequency - The number of waves per second (Hz)
Wave calculations (p.51)
Sound waves travel 340m/s through air.
Humans can hear sounds with frequencies of about 20-20,000Hz.
Think-pair-share: how would a speaker make a sound with a frequency of 20,000Hz?
If a sound wave has a frequency of 20Hz, how long would each wave be?
If the frequency were doubled, what would happen to the speed of the sound? What would happen to the length of each wave?
What is the relationship between the frequency and the wavelength?
If the frequency stays the same and the wavelength doubles, what happens to the speed? What if the wavelength stays the same, but the frequency is doubled?
Can you come up with an equation to relate the frequency, wavelength and speed of a wave?
Wave equation (p.51)
v=f𝜆
v = the speed of the wave (in m/s)
f = the frequency of the wave (in waves/s; Hz)
𝜆 = wavelength (in m)
It makes sense that if we take the number of waves produced in one second and multiply it by the length of each wave, it will give us the total distance covered in one second.
Check for understanding: Humans can hear sounds from about 20Hz-20,000Hz. What is the shortest wavelength traveling through the air that a person could hear?
Exit Ticket
Exit ticket: What is the frequency of a sound wave traveling through air with a wavelength of 2m? Is that a low pitch or high pitch sound?
Mechanical Waves (p.49)
Mechanical waves are vibrations (energy) that move through material (such as air, water, the ground or a slinky) without transferring matter.
Example include earthquakes, ocean waves, and slinkys.
The wave is not the medium itself, but the energy that moves through the medium.
Ex. in the ocean, a “wave” is the energy that moves the water up and down, not the water itself.
Draw a duck sitting on the water when a gentle wave goes by.
Exit Ticket
Exit ticket: What is a sound wave? How does it travel?
Longitudinal vs. Transverse Waves (p.49)
Transverse waves: The movement of the material is perpendicular to the direction of movement of the wave.
Longitudinal waves: The movement of the material is parallel to (in the same direction as) the movement of the wave.
Is this an example of a transverse wave or a longitudinal wave?
Human example
Exit Ticket
Exit ticket:
1. What was your calculated speed for sound?
2. If you scream in space, would anyone be able to hear you? Why or why not?
Community Circle
Part of the difficulty of being an adolescent is trying to find one’s identity. What struggles have you had trying to figure out who you are and how did you overcome those struggles? How do you develop your own identity?
Exit Ticket
Exit Ticket - What was the speed of sound you determined, how close is that to the actual speed at which sound travels through air?
Homework - Sound waves travel 340m/s. What is the length of one wave for a sound wave with a frequency of 120 waves/second? What is the length of a sound wave with a frequency of 14,000 waves/second?