Waves in Media

Waves in Media

Time to brave some waves

Waves in Various

Media

Success Criteria

I can…

...label and identify parts of a wave.

...solve problems involving Frequency,
Period, and Wavelength.

...identify the type of wave based on
wavelength.

...identify the different effects of waves
based on wavelength and frequency.

UNIT 5 STANDARDS

● HS-PS4-4

○ Evaluate the validity and reliability of claims in published materials of the effects that

different frequencies of electromagnetic radiation have when absorbed by matter.

● HS-PS2-5

○ Plan and conduct an investigation to provide evidence that an electric current can produce a

magnetic field and that a changing magnetic field can produce an electric current.

● HS-PS3-5

○ Develop and use a model of two objects interacting through electric or magnetic fields to

illustrate the forces between objects and the changes in energy of the objects due to the
interaction.

● HS-ESS2-4

○ Use a model to describe how variations in the flow of energy into and out of Earth’s systems

result in changes in climate.

01

Recap

02

Introduction

03

Examples

Recap

01.

Recap Topic: Anatomy of a Wave

SECTION 1 – INTRODUCTION TO WAVES
ANATOMY OF A WAVE

● Wave: The repeating and periodic disturbance that

moves through a medium from one location to
another. Transfers energy, not matter. One full “cycle”
is a wavelength.

● Crest: Point of the wave that exhibits the maximum

amount of upward displacement. (The highest points of
the waves.)

● Trough: Point of the wave that exhibits the maximum

amount of downward displacement. (The lowest points
of the waves.)

● Amplitude: The maximum amount of displacement

from the resting position (the height of the wave, also a
measure of energy in the wave).

● Equilibrium: The natural resting place of an object.

Learning Intention: I am learning how waves are used to transfer energy and information.

Remember! A wavelength is the length of a
full cycle.

You can easily find a full cycle by going
crest-to-crest or trough-to-trough.

Introduction

02.

Period and Frequency

Wave Speed

​

● We began our discussion about waves by talking about their parts.
● One part we talked about was the medium.
● Today we will continue that discussion by analyzing the effect that mediums have on the waves that are moving through them.

● To do this, let’s start by talking about light again.

​Full Circle

PHOTONS

● Photons are particles that make up light.

● Photons are massless.

● All photons move at the speed of light, 300,000,000meters per second, or 670,000,000 miles per hour.

● The entire basis of a photon’s existence is the energy it carries. Because it has no mass, it can’t be stopped.

• IF a photon were to be stopped… it would transfer its energyand disappear.

HOW FAST IS THE SPEED OF LIGHT?

● As stated in the previous slide, the speed of light is

300,000,000 meters per second, or 670,000,000
miles per hour.

● If you moved at the speed of light, you would be able to circle the globe 7.5 times in one second.

A light-speed aside

● You may have heard the term “lightyear” thrown around before.

● Lightyears are not a unit of time, but a unit of distance.

○ A lightyear is the distance that light travels in one year.

● As an example, you may state that an object is “five lightyears away”.

● This same naming structure can be used while describing shorter

distances as well. Ex. Lightseconds and lightminutes.

Particle or Wave?

● Consider: last week when we (briefly) talked about electromagnetic waves (which includes light), we clearly discussed waves.

● Now, we’re talking about light as though it is a particle. What gives?

● Honestly, we don’t really have a good way to describe electromagnetic

waves’ behavior.

○ Sometimes, they follow behavior typical of a particle, and other times they behave similar to waves.

● What’s actually happening is we change the way we describe

electromagnetic waves based on what we need to explain happening.

The Electromagnetic Spectrum - Revealed

● So now, let’s take a look at the Electromagnetic Spectrum.

● As you across the spectrum, the wavelength and frequency of the waves shift.

● If we turn our attention to the section that details visible light, we see

that light also behaves that way.

​

Visible Light

● Take a look at this image. You’re probably familiar with the idea behind a

prism. White light comes in, and is split into multiple colors.

● The light is bent as it comes into the prism and disperses depending on

the wavelength of the wave.

● This results in multiple colors coming out of the prism.
● Now that we know what is happening, let’s figure out why it happens.

Mediums

● As a wave leaves one medium and enters another, there is some bending

that has to happen to account for what the wave is traveling through.

● The reason this happens is that the speed of the wave is affected by the

medium it travels through.
○ Consider running across cement and suddenly running onto sand. Your speed would

drop because of the surface you are running on (traction and such).

● So what slows down light?

○ Particles! Lots and lots of particles. Imagine trying to navigate through a busy train

station. That’s what light is going through as it travels through a medium!

○ This means the vacuum of space is the easiest thing for light to travel through (and

because of this, the speed of light refers specifically to the speed light travels in a
vacuum.

Refraction

● So as a wave enters another medium, if it slows down or speeds up, the

wave will change speeds and bend because of it.

● The bending of the wave is what’s known as refraction.

○ Refraction is governed by what’s known as Snell’s Law.

● Snell’s Law uses what we know about light entering a medium and

changing speeds in order to predict how light will bend upon
encountering the aforementioned medium.
○ The ratio of the speed of the wave in a vacuum to the speed of the wave in the new

medium gives us a value known as the Index of Refraction.

○ The Index of Refraction is generally a known value.

Refraction

● So as a wave enters another medium, if it slows down or speeds up, the

wave will change speeds and bend because of it.

● When light enters a different medium, it undergoes a process called

refraction.
○ Refraction is governed by what’s known as Snell’s Law.

● Every medium has a different refractive index.
● The refractive index is a measure of how much light slows down as it

enters the new medium.

Section 1: Light
Refraction (2): Snell’s Law
● When light passes from one medium to another, we

can figure out the angle at which it will bend.

● This is called Snell’s Law.

● This equation states that the ratio of speeds is directly related to the ratio between the indices of refraction. It also is telling us that the ratio of the sine of the angle is related to the speed and indices of refraction.

Section 1: Light
Refraction (3): Snell’s Law
● There are a few different ways to look at this

equation.

● First: n1sin(𝜃1) = n2sin(𝜃2).
● This form is the standard form of Snell’s Law, and

generally the go-to.

Section 1: Light
Refraction (3): Snell’s Law

● What this tells us, intuitively, is that if our n1 > n2, thenthe light will bend away from the normal.
○ This means that the speed of the wave increased when it entered the new medium.

● If our n2 > n1, then the light will bend towards the

normal.
○ This means the speed of the wave decreased when it

entered the new medium.

Odds and Ends

● Some unaddressed questions:

○ Is ALL light refracted?

■ No. Not all light is refracted. Looking at our example from earlier, notice that some of the

light is actually reflected. Depending on the angle the ray hits, it may not even enter the
new medium.

○ Do other waves undergo refraction?

■ Yes! All waves undergo refraction when entering a new medium. They may not visibly show

it, but they certainly change speed when they enter new mediums.