# Physical Science B SGI Lesson #14 (2-27-2019)

Waves

8

### Objectives:

• Explain that waves transfer energy, not matter.
• Distinguish between mechanical and electromagnetic waves.
• Summarize the major properties and behavior of waves, including (but not limited to) wavelength, frequency, amplitude, speed, refraction, reflection and diffraction.

### Vocabulary/Definitions

amplitude: How far the medium (crests and troughs, or compressions and rarefactions) moves from rest position (the place the medium is when not moving).

compression: When the particles of a longitudinal wave are close together.

compressional (longitudinal) wave: A wave in which the medium moves back and forth in the same direction as the wave.

crest: The highest point on a transverse wave.

diffraction: The bending of waves around an object.

electromagnetic wave: A wave that does not require a medium to travel, for example, it can travel through a vacuum. Also called an EM wave.

energy: The capacity to do work.

frequency: How many waves go past a point in one second. Measured in hertz (Hz).

mechanical wave: A wave that requires a medium to travel.

rarefaction : When the particles of a longitudinal wave are far apart.

reflection: When a wave bounces off a surface.

refraction: When a wave bends.

transverse wave: A wave in which the medium moves at right angles to the direction of the wave.

trough: The lowest point on a transverse wave.

wave: A disturbance that carries energy from one place to another.

wavelength: Distance between one point on a wave and the exact same place on the next wave.

additive color system: Involves light emitted directly from a source, before an object reflects the light. Mixes various amounts of red, green and blue light to produce other colors. Examples include computer monitors and TVs.

concave or negative lens: A lens that diverges or spreads out light rays.

convex or positive lens: A lens that converges or focuses light, and can form images.

cyan: A highly saturated green-blue that is the complementary color of red and forms, with magenta and yellow, a set of primary colors.

laser: Acronym for light amplification by stimulated emission of radiation. Lasers only produce one wavelength of light, resulting in a beam of light that is very distinct and does not spread out.

opaque: A characteristic of an object that does not allow light to pass through; it absorbs or reflects all light.

prism : A transparent optical object that refracts light.

subtractive color system: Creates color by subtracting or absorbing certain wavelengths of color while reflecting other wavelengths back to the viewer. Examples include photographs and printed magazines.

translucent: A characteristic of an object that can be seen through, but not clearly; it absorbs, reflects and transmits light, such as wax paper or frosted glass.

transparent: A characteristic of an object that allows almost all the light to pass through, so it can be seen through clearly, such as glass or clear plastic.

electromagnetic radiation: A phenomenon that takes the form of self-propagating waves in a vacuum or matter. It is comprised of electric and magnetic field components that oscillate in phase perpendicular to each other and the direction of energy propagation. All travel the speed of light.

electromagnetic spectrum: The range of all possible frequencies of electromagnetic radiation.

### Engineering Connection

Engineers apply their knowledge of waves to design an array of useful products and tools, many of which are evident in our everyday lives. For example: microwave ovens, x-ray machines, eyeglasses, tsunami prediction, radios and speakers. Engineers must understand all the properties of waves and how waves can differ from one another in order to design safe and effective products. To predict how tsunamis will travel after a ocean earthquake, engineers must understand wave properties and how they travel. Engineers also use their understanding of wave properties when designing electronics—to separate different types of waves so that radios tune in to the right stations, or so your cell phone only picks up the calls that you want. Before designing a solution to a challenge, engineers conduct research and gather information as a crucial part of the engineering design process. Through this legacy cycle lesson, students begin to gather the knowledge necessary to come up with a solution to the engineering challenge outlined in lesson 1 of this unit.

### Task #1 (Vocabulary Quiz, Yup Again)

Let us see how much studying we have been doing regarding our vocab terms for this unit and how much we have improved since Monday.

Enter “A89559b4”

Lecture -> Presentation – Properties of Light

Click on the following folder link to be taken to the submitted presentations -> Unit 8 Physical Science Vocab Presentations

Only presentations that were complete by the deadline were posted for peer review. If you did not get your presentation done it still needs to be complete as it is part of this unit. You can CLICK HERE to see the status of your presentation confirmed.

After you have reviewed all the presentations, yes names have been removed to protect anonymity, vote below on the presentation that you feel was the best one. Each computer can only vote once, you can keep trying to submit multiple votes, but they are only counted one time. The winner of this project will have earned a \$25 DOLLAR AMAZON GIFT CARD!!!!!

### Task #4 (Intro to Electromagnetic Spectrum)

The Electromagnetic Spectrum

The EM Spectrum is the complete (entire) range of EM waves in order of increasing frequency and decreasing wavelength. This means as you look from left to right on a diagram of the spectrum, the wavelengths get smaller and the frequency gets larger. An inverse relationship exists between size of the wave and frequency. Remember: all EM waves travel at the same speed: 300,000km/s. If you remember the formula for speed, it is the wavelength times the frequency. For the answer to always be 300,000km/s, as one number goes up, the other must go down. All EM waves are radiation. It is just that the longer wavelengths do not carry enough energy in them to damage cells. Remember: the higher the frequency, the more energy in the wave!

Waves in the Spectrum

Radio waves have the longest wavelengths and lowest frequencies; wavelengths range from 1000s of meters to 0.001 m. (The shortest radio waves are microwaves.) Radio waves are used in RADAR (radio detection and ranging), sending sound, pictures (TV), cell phones, cooking and satellite transmissions.

Infrared waves (heat) have shorter wavelengths, from 0.001 m to 700 nm and higher frequencies (a nm is one billionth of a meter). Infrared is used to find people in the dark and in TV remotes.

Visible light is what we can see in the EM spectrum. Wavelengths of visible light range from about 700 nm (red light) to 400 nm (violet light). Visible light frequencies are higher than the frequencies of infrared waves. Notice how visible light is such a small portion of the entire spectrum.

Ultraviolet wavelengths range from about 400 nm to 10 nm; the frequency (and therefore the energy) is high enough with UV rays to penetrate living cells and cause them damage. We need UV rays to produce vitamin D in our bodies. Even though too much can lead to sunburn and skin cancer, UV rays are easily stopped by clothing. UV rays are used for sterilization of materials because they kill bacteria in high enough concentrations. Although humans cannot see UV light, bees, butterflies, some small rodents, and some birds can.

X-rays have wavelengths from 10 nm to 0.001 nm. They have enough energy to penetrate deep into tissues, but are stopped by dense materials, such as bones. Used for examining solid structures (such as looking for cracks in bones and bridges), and for cancer treatments.

Gamma rays have the shortest wavelengths (less than one trillionth of a meter: 10 to the negative 12), therefore the highest frequencies, therefore carry the most energy. These are the most damaging to tissues and can penetrate the deepest. They are hard to stop! You would need a 3–4 foot thick concrete wall to stop them. Gamma rays are released in nuclear power plants, by nuclear bombs, and by naturally occurring elements on Earth. They are sometimes used in the treatment of cancer.

Assignment -> Physical Science Unit 8 – Electromagnetic notes

### Task #5 (The Human Eye)

Now we have come full circle from the initial activity we did on this unit…. The Human Eye.

Assignment -> Eye Structure and Seeing Light—Notes Outline

### State Standards:

Disciplinary Core Ideas

PS4.A: Wave Properties

• Sound can make matter vibrate, and vibrating matter can make sound. (1-PS4-1)

• Objects can be seen if light is available to illuminate them or if they give off their own light. (1-PS4-2)
• Some materials allow light to pass through them, others allow only some light through and others block all the light and create a dark shadow on any surface beyond them, where the light cannot reach. Mirrors can be used to redirect a light beam. (Boundary: The idea that light travels from place to place is developed through experiences with light sources, mirrors, and shadows, but no attempt is made to discuss the speed of light.) (1-PS4-3)

PS4.C: Information Technologies and Instrumentation

• People also use a variety of devices to communicate (send and receive information) over long distances. (1-PS4-4)

### Lesson Sources:

Website – TeachEngineering STEAM – Apples

Website – TeachEngineering STEM Curiculum K-12

Website – Light Properties

Website – NGSS for California Public Schools

Website – The Human Eye in Engineering