Waves. Learning Objectives TLW know the characteristics and behaviors of waves (TEKS 7) TLW conduct...

Waves

Learning Objectives• TLW know the characteristics and behaviors of

waves (TEKS 7)• TLW conduct lab investigations in a safe manner

(TEKS 1)• TLW use scientific methods during lab (TEKS 2)• TLW uses critical thinking and problem solving

techniques to make informed decisions (TEKS 3)

I. What is a Wave?A. Wave – a disturbance that carries

energy through matter

1. The matter through which a wave travels is called a mediumEx. A rock thrown in water = water is the medium

Ex. A stereo playing music = air is the medium

Ex. Earthquake travels through earth = ground is the medium (these are called seismic waves)

2. The density of the medium is called

elasticity

3. It is the energy that moves not the matter (or water)

4. A wave can occur in water, air, or space * = anywhere (* except sound doesn’t travel in the vacuum of

space)

5. Sound and light travel as a

wave

Characteristics of Waves

• Wavelength – distance between 2 crests or 2 troughs or any other identical points

• Wave height – distance between a crest and a trough

• Amplitude – ½ the distance between a crest or a trough

Parts of a Wave

Amplitude

Wave height

amplitudewave height

• Frequency – number of wavelengths that pass a point in a certain time

–Also measures how rapidly vibrations occur in the medium

• Wave period – the time required for 1 wavelength to pass a certain point

CalculationsA mathematical relationship exists between wave speed

(velocity), wave length, and frequency

Wave speed = wavelength x frequency

It can be described by the formula:

v = λ f

Where

v = wave speed in m/s (velocity = distance/time)

λ = wavelength in m

f = frequency in Hz (which is the same as 1/sec)

or f = 1/T where T is time in seconds

Practice Calculation

If a wave has a wavelength of 10 m and a frequency of 2 Hz, what is the wave speed?

Given: v = λ f

λ = 10 m (10 m)(2 Hz)

f = 2 Hz 20 m/s

B. Types of Waves

1. Mechanical Waves

a. Any wave that travels through a medium is a mechanical wave

b. Ex. Sound waves, water waves, seismic waves

c. Almost ALL waves are mechanical waves

2. Electromagnetic Wavesa. A wave that does NOT require a

medium

b. Occurs when energy “travels”

through electric and magnetic

fields by being propagated

by sub-atomic particles called

photons

c. Ex. Visible light, radio waves, x-rays

Wave-Particle Duality

• The theory that electromagnetism is made up of both energy and particles of matter (photons)

3. Movement of particles in mediuma. when a wave occurs particles

in the medium will moveb. particles will either move up

and down or back and forth

c. Waves are classified by thedirection the particles

move in a medium as a wave passes

d. Types of waves based on particle movement

1. Transverse waves

a. travels through solids, liquids &

gases

b. particles move perpendicular

or up and down

c. Bunched up part is called

compression

Transverse wave

2. Longitudinal waves

a. travels through solids,liquids & gases

b. a parallel motion or back & forth

Longitudinal wave

Types of Waves

Common Stuff

• Threshold of human hearing is 1,000 Hz (0 decibels – dB)

• Threshold of pain in human hearing is 4,000 Hz (120 dB)– Rock concert (100 – 150 dB)

• Any sound above 20,000 Hz is called ultrasound – like the safer way to observe an unborn child or lump

• The frequency of a sound wave is called pitch as a sensation (high frequency, high pitch)

More Common Stuff

• Range where humans can detect light is 400 nm – 700 nm (ROYGBIV)

C. Surface Waves1. If a wave has both transverse

and longitudinal waves it is called a surface wave

2. Ex. Ocean waves are examplesof surface waves

II. How a Wave WorksA. Energy must be transferred

1. Waves carry energy

2. the bigger the initial wave the more energy it has

B. The energy spreads out

1. waves spread out in spheres called wave fronts

2. as waves move away from the “center” the spheres or circles get larger

3. the entire wave has the same amount of total energy

4. but as the wave gets larger, that energy is more spread out

5. Eventually, the waves become so large that the energy is not “noticeable”

6. Ex. throwing a rock in a pond – the waves become larger and weaker the further

from the center it travels

Sound – the further from source the harder it is to hear

• TRUE or FALSE: In order for John to hear Jill, air molecules must move from the lips of Jill to the ears of John.

  • Curly and Moe are conducting a wave

experiment using a Slinky. Curly introduces a disturbance into the Slinky by giving it a quick back and forth jerk. Moe places his cheek (facial) at the opposite end of the slinky. Using the terminology of this unit, describe what Moe experiences as the pulse reaches the other end of the slinky.

• Rhonda sends a pulse along a rope. How does the position of a point on the rope, before the pulse comes, compare to the position after the pulse has passed?

  • Why don't incoming ocean waves bring more water onto

the shore until the beach is completely submerged?   In order for a medium to be able to support a wave, the

particles in the medium must be – frictionless. – isolated from one another. – able to interact. – very light.

Reflection

http://www.slideshare.net/amandayoung313/how-do-waves-behave

Refraction

http://www.slideshare.net/amandayoung313/how-do-waves-behave

Diffraction

http://www.slideshare.net/amandayoung313/how-do-waves-behave

Interference

http://www.slideshare.net/amandayoung313/how-do-waves-behave

Destructive Interference

When wave interference is in the opposite direction.

This action tends to reduce amplitude of disturbance.

Constructive Interference

When wave interference is in the same direction.

This action tends to increase amplitude of disturbance.

Standing Waves

• Successive waves that interfere with each other in a way that causes them to stand still

Resonance•Resonance means to resound or sound again•When the frequency of a force vibration on an object matches the object’s natural frequency, a dramatic increase in amplitude occurs – this phenomenon is called resonance

•This is how tuning forks work

•Not only sound, but vibration in generalResonance from a mild gale force wind of 40 mph with the natural frequency of the Tacoma Narrows Bridge (in Washington state) in 1940 caused collapse in just one hour… only 4 months after bridge was completed

http://www.youtube.com/watch?v=3mclp9QmCGshttp://www.youtube.com/watch?v=j-zczJXSxnw

RarefractionDecrease in density and pressure in a medium, such as air, caused by the passage of a sound wave.

Rarefaction can be easily observed by compressing a spring and releasing it. Instead of seeing compressed loops seeming to move through the spring, spaced-out loops move through it: rarefaction waves.

The Doppler EffectThe apparent frequency of a sound changes due to the relative movement of the source and/or observer

YouTube - Fire Engine siren demonstrates the Doppler Effect

Uses of the Doppler Effect

• Measuring the speed of moving objects (like cars or baseballs)

• Measuring the speed of flow of blood cells in an artery

• Meteorologists use the Doppler Effect to track storm systems

• The same effect occurs with light waves. This is how scientists have proven the universe is expanding (called the Red Shift)

• Doppler Slides from Google link

Lens• Lens are optical devices that transmit and

refract light

eye glasses, microscopes

• Converging lenses focus

light to a single point

• Diverging lenses

spread the light outward

Web Waves

Discovery Education web video

Elements of Physics: Waves: Sound and Electromagnetism

link

Labs

• In Periodic Groups review entire procedure

• Determine any potential hazards, precautions to take, and PPE needed (if any)

• Complete any pre-work associated with lab

• Set up experiment and report using scientifc method

Lab

• Various options