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
|Essential Question: What's the difference between an AM and FM radio signal?|
Solve problems involving sideband frequencies and bandwidth.
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
Describe, by means of a block diagram, an AM radio receiver.
--creates an electromagnetic field by moving electrons back and forth in the antennae. Best performance generally occurs when the system is designed to resonate.
|Essential Question: How has digital data transmission revolutionized communication?|
Solve problems involving the conversion between binary numbers and decimal numbers.
--a binary digit
least-significant bit (LSB) 10111001
most-significant bit (MSB)
Distinguish between analogue and digital signals.
--infinite number of possible values between the lowest and highest output
digital--finite number of possible values between the lowest and highest output determined by the number of bits
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
Describe, using block diagrams, the principles of the transmission and reception of digital signals.
analogue-to-digital converter (ADC)
digital-to-analogue converter (DAC)
Explain the significance of the number of bits and the bit-rate on the reproduction of a transmitted signal.
number of bits
Describe what is meant by time‑division multiplexing.
Solve problems involving analogue‑to-digital conversion.
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
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.
Discuss the moral, ethical, economic and environmental issues arising from access to the Internet.
|Essential Question: How can glass transmit data?|
Optic fiber transmission
--the angle needed for total internal reflectance
total internal reflection
Solve problems involving refractive index and critical angle.
θcr = sin-1 (n1 / n2)
Derived from Snell's Law:
n1 sin( θ1) = n2 sin(θ2)
n = index of refraction
= (speed of light in a vacuum) / (speed of light in the media)
θ = incident angle
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
Describe the effects of material dispersion and modal dispersion. (attenuation per unit length measured in dB km–1)
--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.
Explain what is meant by attenuation and solve problems involving attenuation measured in decibels (dB).
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
State what is meant by noise in an optic fibre.
in optic fibre transmission, describe the role of
--boosts the power of the light signal
Solve problems involving optic fibres.
|Essential Question: How is data communicated?|
Channels of communication
Outline different channels of communication:
--two wires with currents flowing in opposite directions are twisted together so that the EM field produced by each wire cancels each other. Likewise any current induced in the pair of wires from an outside EM field will also be canceled out. For example, CAT 6 cable is for gigabit transmission rates with performance of up to 250 MHz. maximum allowed length of a Cat-6 horizontal cable = 100 meters (330 ft). Wires are relatively inexpensive and easy to install.
radio waves and satellite communication
Discuss the uses and the relative advantages and disadvantages of wire pairs, coaxial cables, optic fibres and radio waves.
cost and handling
State what is meant by a geostationary satellite.
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.
Discuss the relative advantages and disadvantages of the use of geostationary and of polar-orbiting satellites for communication.
Discuss the moral, ethical, economic and environmental issues arising from satellite communication.
|Essential Question: What is an op-amp and why is it revolutionary?|
State the properties of an ideal operational amplifier (op-amp).
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.
|Essential Question: Are mobile phone communications private?|
The mobile phone system