Mr. Rogers' IB Physics Topics
Syllabus 1st Quarter 2nd Quarter 3rd Quarter 4th Quarter
IB HL Thermo SL Waves HL Waves Communications EM Waves

 

Option F: Communications

 

Objectives
Essential Question: What's the difference between an AM and FM radio signal?

 

Radio communication

  1. Describe what is meant by the modulation of a wave.

  2. Describe the nature of amplitude modulation (AM) and frequency modulation (FM).

  3. Solve problems based on the modulation of the carrier wave in order to determine the frequency and amplitude of the information signal.

  4. Sketch and analyze graphs of the power spectrum of a carrier wave that is amplitude-modulated by a single‑frequency signal. (see figure 1)

  5. Define (see ref):

sideband frequencies

bandwidth

 

Figure 1: Power Spectrum of a Carrier Wave  Amplitude-Modulated by a Single‑Frequency

 

  1. Solve problems involving sideband frequencies and bandwidth.

  2. Describe the relative advantages and disadvantages of AM and FM for radio transmission and reception.

  AM FM
quality Poor: bandwidth limited but this is a property of current broadcast systems not of AM. However, amplitude is susceptible to noise and attenuation Good to excellent: generous band width available for stereo-audio but this is a property of current broadcast systems not of FM. However, frequency generally is not susceptible to noise or attenuation.
bandwidth Low (10 kHz): typically broadcast at lower frequencies, 540 to 1600 kHz for 160 stations. (ref) but this is a property of current broadcast systems not of AM. Higher (200 kHz): typically broadcast at higher frequencies, 88.1 to 108.1 MHz for 100 stations. (ref) but this is a property of current broadcast systems not of FM.
range Better with all things equal, but this is primarily caused by the lower frequencies used, not by AM. Worse with all things equal but this is primarily caused by the higher frequencies used, not by FM.
cost Lower: broadcast equipment is less complex. Higher: broadcast equipment is more complex

  1. Describe, by means of a block diagram, an AM radio receiver.

 

Essential Question: How has digital data transmission revolutionized communication?

Digital signals

  1. Solve problems involving the conversion between binary numbers and decimal numbers.

  1. Distinguish between analogue and digital signals.

  1. State the advantages of the digital transmission, as compared to the analogue transmission, of information. (see ref)
  Analog Digital
Accuracy of pure signal precise depends on number of bits
Error checking no yes, example: parity check
Error Correction no yes
Susceptibility to noise high low
Flexibility low high. Can send many types of information over the same connection
Multiplexing difficult easy
Bandwidth Required for Transmission lower higher

 

  1. Describe, using block diagrams, the principles of the transmission and reception of digital signals.

  • sample‑and‑hold,

  • clock

  • analogue-to-digital converter (ADC)

  • parallel‑to-serial converter

  • serial-to-parallel converter

  • digital-to-analogue converter (DAC)

  1. Explain the significance of the number of bits and the bit-rate on the reproduction of a transmitted signal.

  • number of bits--resolution

  • bit-rate--audio frequency range (sampling rate must be 2x the highest frequency) or amount of information. Generally, for broadcasts, the higher the carrier frequency the higher the information transfer rate.

  1. Describe what is meant by time‑division multiplexing. Several channels of information are sent over a single carrier by allocating time slots to each channel.

  2. Solve problems involving analogue‑to-digital conversion.

example: how many bits would be needed to represent a 0 to 1000 degree C temperature scale?

2 ^ (bits) = 1000

ln[2 ^ (bits)] = ln 1000

0.693 (bits) = 6.908

(bits) = 6.91 / 0.693

          = 9.97 since we always round up = 10

  1. Describe the consequences of digital communication and multiplexing on worldwide communications.

  • cost and availability to the general public

  • quality of transmission

  • communication and data sharing such as the Internet.

  1. Discuss the moral, ethical, economic and environmental issues arising from access to the Internet.

 

Essential Question: How can glass transmit data?

Optic fiber transmission

  1. Explain:

  • critical angle--the angle needed for total internal reflectance

  • total internal reflection--when a ray of light strikes the boundary between two transparent materials and is reflected back into the first material without passing into the second.

  1. Solve problems involving refractive index and critical angle.

θcr = sin-1 (n1 / n2)
where:
n1 < n2  typically material 2 is more dense than material 1

Derived from Snell's Law:

n1 sin( θ1) = n2 sin(θ2)

 

Where:

n = index of refraction

   = (speed of light in a vacuum) / (speed of light in the media)

 

θ = incident angle

 

  1. Apply the concept of total internal reflection to the transmission of light through a step-index optic fiber. (ref)

step-index fiber--the fiber core is clad with a material having a slightly lower index of refraction (n). Done properly, this enhances total internal reflection.

Δ = (ncore - ncladding) / ncore << 1

ncore = typically between 1.44 and 1.46

Δ = typically between 0.001 and 0.02

 

  1. Describe the effects of material dispersion and modal dispersion. (attenuation per unit length measured in dB km–1)

material dispersion--the light used to transmit the signal always has some spectrum width (combination of different frequencies of light). Since materials transmit different wavelengths of light at different speeds (the reason prisms create rainbows), the signal becomes spread out as it travels through the optical fiber.

modal dispersion--the light used to transmit the signal enters the fiber over a range of angles with respect to the axis of the fiber (we're modeling light using rays). Generally, the higher the angle the greater the number of times the ray of light will be reflected and the longer the distance the ray will travel through a given length of cable. This causes the pulse of light to be spread out.

  1. Explain what is meant by attenuation and solve problems involving attenuation measured in decibels (dB). (attenuation per unit length measured in dB km–1) (ref)

for power dB = 10 log (P1/P2)

for amplitude dB = 20 log (A1/A2)

Attenuation (dB)  Remaining Power
1 0.79
3 0.50
10 0.1
20 0.01
30 0.001
40 0.0001

  1. State what is meant by noise in an optic fibre.

  2. in optic fibre transmission, describe the role of

  1. Solve problems involving optic fibres.

 

Essential Question: How is data communicated?

Channels of communication

  1. Outline different channels of communication:

  1. Discuss the uses and the relative advantages and disadvantages of wire pairs, coaxial cables, optic fibres and radio waves.

  • noise

  • attenuation

  • bandwidth

  • cost and handling

  1. State what is meant by a geostationary satellite.

  2. State the order of magnitude of the frequencies used for communication with geostationary satellites, and explain why the up-link frequency and the down-link frequency are different.

  3. Discuss the relative advantages and disadvantages of the use of geostationary and of polar-orbiting satellites for communication.

  4. Discuss the moral, ethical, economic and environmental issues arising from satellite communication.

 

Essential Question: What is an op-amp and why is it revolutionary?

Electronics

  1. State the properties of an ideal operational amplifier (op-amp). A DC-coupled high-gain electronic voltage amplifier with differential inputs and, usually, a single output.

  • infinite input impedance at the input terminals--zero input current

    •

  • zero output impedance

  • infinite open-loop gain (i.e., when doing theoretical analysis, limit should be taken as open loop gain Gopenloop goes to infinity)

  • infinite bandwidth

    •

  • infinite slew rate (i.e., the rate of change of the output voltage is unbounded)

  • zero offset voltage (i.e., when the input terminals are shorted so that V + = V − , the output is a virtual ground).
    •

 
  1. Draw circuit diagrams for both inverting and non-inverting amplifiers (with a single input) incorporating operational  amplifiers. (ref)
  2. Derive an expression for the gain of an inverting amplifier and for a noninverting amplifier. Students should be aware of the virtual earth approximation.
  

  1. Describe the use of an operational amplifier circuit as a comparator.

  • draw appropriate circuits.

  • Output devices for comparator circuits may include light-emitting diodes (LEDs) and buzzers.

  1. Describe the use of a Schmitt trigger for the reshaping of digital pulses. (ref1, ref2)

  • triggers at a specific level and remains triggered until input falls below the chosen level.

  • can convert a given waveform to a square wave output.

  1. Solve problems involving circuits incorporating operational amplifiers.

 

 

Essential Question: Are mobile phone communications private?

The mobile phone system

  1. State that any area is divided into a number of cells (each with its own base station) to which is allocated a range of frequencies. Students should know that frequencies are allocated so as to avoid overlap between cells.

  • conventional broadcast between X and Y -- the signal has to be powerful in order to reach the desired distance. While X is broadcasting, no one in an area greater in radius than the distance from X to Y can use the frequency.

  • cell phone communication between A and B --"A" broadcasts a weak signal to a local tower that then relays the signal via telephone lines to a distant tower. This tower then broadcasts a weak signal to the receiver at B. Only a very small area is prevented from using the same frequency.

  1. Describe the role of the cellular exchange and the public switched telephone network (PSTN) in communications using mobile phones. The role of the cellular exchange in the selection and monitoring of base stations and the allocation of channels should be understood.

  2. Discuss the use of mobile phones in multimedia communication.

  • high carrier frequency enables high band width and high data rate

  • digital signal enables flexibility for text, video, or graphics

  • spread spectrum provides some level of privacy

  1. Discuss the moral, ethical, economic, environmental and international issues arising from the use of mobile phones.

    2.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Mr

SAM Team--Southside High School's STEM and Computer Science extra-curricular club (Mr. Rogers Sponsor)

Mr. Rogers' Twitter Site

Mr. Rogers Teacher's Blog

Mr. Rogers T-shirts

Mr. Rogers Information for Teachers

Mr. Rogers Science Fair Information

Check out other web sites created by Mr. R:

Check out Articles by Mr. Rogers:

  
Insultingly Stupid Movie Physics is one of the most humorous, entertaining, and readable physics books available, yet is filled with all kinds of useful content and clear explanations for high school, 1st semester college physics students, and film buffs.

It explains all 3 of Newton's laws, the 1st and 2nd laws of thermodynamics, momentum, energy, gravity, circular motion and a host of other topics all through the lens of Hollywood movies using Star Trek and numerous other films.

If you want to learn how to think physics and have a lot of fun in the process, this is the book for you!

 

First the web site,

now the book!

Mr. Rogers Home | Common Sylabus | AP Comp Sci I | AP Comp Sci II | AP Physics Mech | AP Physics E&M | AP Statistics | Honors Physics|IB Design Tech | Southside

[ Intuitor Home | Physics | Movie Physics | Chess | Forchess | Hex | Intuitor Store |

Copyright © 1996-2011 T. K. Rogers, all rights reserved. Forchess ® is a registered trademark of T. K. Rogers.
No part of this website may be reproduced in any form, electronic or otherwise, without express written approval.