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# BTEC: Waves and Communication

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## Paul Sheffield

on 21 November 2018

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#### Transcript of BTEC: Waves and Communication

Wave speed
Overview
Unit 1: Section C
Exam in January
Assignment B
Do it now!
What is a wave?
Name the different types of waves?
Give examples of each
Draw and label a wave diagram
What is the wave equation?
Waves in communication
L.O
Period
Frequency
Wavelength
Phase
Working with Waves
Oscillation
Frequency
Periodic time
Displacement
Amplitude (max displacement)
Investigating a pendulum
Complete the pendulum practical
Calculate the frequency of the waves at each pendulum length
What do you think happens to wave length?
What are the sources of error for thios investigation?
How did we limit them?
Why do we do repeats?
BTEC: Waves and Communication
Do it now!
Name the two typ of wave
Describe the differences between the two types of wave
What is amplitude?
What is the period of a wave?
what is the frequency of a wave?
Draw a wave diagram for a pendulum and label the stages
Wave equation
Speed= wavelength / Periodic time
easier to use frequency as periods are often very small fractions of time
Speed= frequency X Wavelength
In Phase
Graphical representation of wave features
Crank shaft and circular motion
one complete oscillation of a piston = one complete turn of the crank shaft
same periodic time and frequency
Graphs are typically sine waves for circular motion.
Phase
Phase= same point same thing
Out of phase not the same point or thing
Phase difference= difference in phase angle between two waves of the same frequency and wavelength
360 degrees or 2 pi raans represents a single whole cycle of wave form
Radans
Degrees measure angles by how far we tilted our heads. Radians measure angles by distance traveled.

But absolute distance isn’t that useful, since going 10 miles is a different number of laps depending on the track. So we divide by radius to get a normalized angle:

A circle has 360 degrees or 2pi radians — going all the way around is 2 * pi * r / r. So a radian is about 360 /(2 * pi) or 57.3 degrees.

Now don’t be like me, memorizing this thinking “Great, another unit. 57.3 degrees is so weird.” Because it is weird when you’re still thinking about you!

Moving 1 radian (unit) is a perfectly normal distance to travel. Put another way, our idea of a “clean, 90 degree angle” means the mover goes a very unclean pi/2 units. Think about it — “Hey Bill, can you run 90 degrees for me? What’s that? Oh, yeah, that’d be pi/2 miles from your point of view.” The strangeness goes both ways.

Radians are the empathetic way to do math — a shift from away from head tilting and towards the mover’s perspective.

What’s In A Name?
Radians are a count of distance in terms of “radius units”, and I think of “radian” as shorthand for that concept.

Strictly speaking, radians are just a number like 1.5 or 73, and don’t have any units (in the calculation “radians = distance traveled / radius”, we see length is divided by length, so any units would cancel).

But practically speaking, we’re not math robots, and it helps to think of radians as “distance” traveled on a unit circle.
Waves and Communication
L.O
Graphically representing waves
Polarising of Electromagnetic waves
Do it now
What is wavelength?
What is phase difference?
What is the frequency of a wave?
What is amplitude?
What is the frequency of a wave if it has a speed of 300,000,000 m/s and a wavelength of 1m?
Figure 1.43
use this graph to draw out the graph for a rotating vector.
label the phase angles in dergrees and radians
Figure 1.44 and 1.46
cut out these graphs and stick them in your notes
explain what they show
Diffraction
Polarisation of light

how expensive sunglasses work
can be done to aall electromagnetic waves
only allow light from one plane
removes glare from reflected surfaces
Full transcript