# WaveVariables

Wavelength

the Wavelength is the distance between 2 equal but separate and adjacent points along a wave.

the Wavelength is closely related to the actual size of the vibration/distortion that caused the wave in the 1st place.

This in turn relates to the energy of the wave, more of this later

Amplitude

Amplitude is the size of the wave this contributes more of the power of the wave

Frequency

Bus routes can be described by their frequency, how many No. 39 buses run everyday? The 220 route how many of them come

So how many come per hour?

Frequency is a count of incidents per time unit. The number of Bus journeys per day on different routes informs us which routes are the busiest.

In terms of waves we are counting the number of waves in a second !

but a wave is continuous, it does not stop.

So we need to count the number of wave segments

Lauch Audacity and check file wavefrequency1

How many wave segments are in this wave? How can you tell ?

Zoom out again, what is all you can see?

The wave, why ?

When we were close up we could see the background, why not now?

The Time along the top has gotten bigger

, ...... so _________ is the ............... of waves per ...........

Frequency is often called pitch, and you probably know what a high pitched and low pitched sounds are ....

A high pitch is the same as a high frequency ,

lets check out some different pitches hear here

http://www.fearofphysics.com/Sound/sounds.html

velocity, c

Velocity is the speed that these waves are traveling at through the medium they are travelling.

Media can only allow waves to pass through them at defined velocities.

velocity ,frequency, wavelength,.

Relationship c = f λ

wave velocity = frequency x wavelenght

As we have said the wave velocity in a medium is limited, therefore the product of the wavelength and the frequency is a constant .......

so if we have a large frequency we will have a small wavelength

and the opposite is true

a large ___________ we will have a small __________

Finding the Speed of Light with

Marshmallows - A Take-Home Lab

Robert H. Stauffer, Jr., Cimarron-Memorial High School, Las Vegas, Nevada, USA

I have heard that at 16 years old, Albert Einstein constantly wondered what it would be like to ride on a beam of light. Students in physics always seem to be fascinated by the properties of light. However, speed-of-light demonstrations often require extensive preparation or expensive equipment. I have prepared a simple classroom demonstration that the students can also use as a take-home lab.

The activity requires a microwave oven, a microwave-safe casserole dish, a bag of marshmallows, and a ruler. (The oven must be of the type that has no mechanical motion-no turntable or rotating mirror. If there is a turn-table, remove it first.) First, open the marshmallows and place them in the casserole dish, completely covering it with a layer one marshmallow thick. Next, put the dish of marshmallows in the microwave and cook on low heat. Microwaves do not cook evenly and the marshmallows will begin to melt at the hottest spots in the microwave. (I leaned this from our Food Science teacher Anita Cornwall.) Heat the marshmallows until they begin to melt in four or five different spots. Remove the dish from the microwave and observe the melted spots. Take the ruler and measure the distance between the melted spots. You will find that one distance repeats over and over. This distance will correspond to half the wavelength of the microwave, about 6 cm. Now turn the oven around and look for a small sign that gives you the frequency of the microwave. Most commercial microwaves operate at 2450 MHz.

All you do now is multiply the frequency by the wavelength. The product is the speed of light.

Example:

Velocity = Frequency x Wavelength

Velocity = 2450 MHz x 0.122 m

Velocity = 2.99 ´ 108 m/s

This works in my physics class, often with less than 5% error. Then the students can eat the marshmallows.

Appropriate calculations.

See examples on page 178

Do questions 1-7