Discussion:
1. Design a webpage to advertise a holiday to New York City:
(a) You should:
o Develop the page in native HTML
o Use a simple webpage with a good design and clean visual layout
o Include comments in your code
o Include one or more images
o Include one or more links
o Use Relative Addressing (ie. Where images, CSS, and Javascript are used, put them in separate subdirectories).
o Use CSS
o Use Javascript
(b) Test your browser in at three different web browsers. Give the name and version number of each browser and make a note of any differences you notice in how the three browsers render the page. (10 marks)
Answer All Questions
1(a) In your own words, explain the concepts of electromotive force and potential difference.
1(b) In your own words, describe the concept of a magnetic field.
1(c) Two bar magnets of 10cm height and 10cm width at the pole faces are fixed in position with their respective N and S poles in close proximity. If the total flux is 0.1 webers, calculate the flux density between the two pole faces. Assume that fringing effects are negligible; i.e. all of the flux passes between the pole faces.
1(d) Examine the discussion at: https://en.wikipedia.org/wiki/War_of_Currents and describe why it is more economical to distribute electricity over long distances using AC rather than DC form? Also, given Edison's claims in this discussion in relation to the Electric Chair, are there any differences in the safety of using AC or DC electricity?
2(a) Describe the magnetic field effects that are created by a current flowing in a long straight conductor. In your own words, describe the right-hand rule. Why is bad practice to run data cable alongside AC electrical cables over long distances?
2(b) When a PN junction is forward-biased it behaves like a closed switch (on) and when it is reverse-biased it behaves like an open switch (off). Discuss this statement with use and description of the terms doping, depletion layer and forward/reverse biased.
2(c) Following on from question 2(b), Figure 2 illustrates two diode circuits. In Figure 2(a) a voltage supply of 10V is connected via the positive terminal to a 1.5K ohm resistor, which is in turn connected to the P side of a PN junction diode. The N side of the diode is connected directly to the negative side of the voltage supply. In Figure 2(b) everything remains exactly the same, except that the PN junction is reversed in the circuit.
In each case, calculate the current flowing through the resistor and the voltage drop across the silicon diode. Please assume that a silicon diode has a forward-biased junction potential of 0.7V (see page 3-35 of the notes).
3(a) If we take a 2-input NAND or a 2-input NOR gate and tie the inputs together to a single input line in both cases, determine using a truth table how both type of gates would behave (i.e. is it like a different type of gate)? Using only the same NAND or NOR gate, examine the truth table for both gates and determine how could we get an equivalent behaviour using a different wiring configuration on the input side for both NAND and NOR gates?
3(b) Demonstrate using truth-tables that a 2-input NOR gate is equivalent to a 2-input AND gate with an inverter on each input. Write the algebraic symbols to represent this relationship.
3(c) Using AND, OR and NOT logic gates only, determine a circuit that behaves in the same way as a 2-input XOR gate.
4(a) Show, using a truth table only, that A AB A B . Illustrate the two equivalent circuits.
4(b) Prove that A AB A B using only the remaining rules of Boolean algebra and
the Three Laws, stating each step by referring to the rule number (i.e. this is rule 11 on page 3-50 of the notes - use the other rules to prove rule 12).
Question 5
5(a) An industrial process has 3 safety sensors S1, S2 and S3 to determine if it is working correctly. It also has a safety switch P that can be pressed to cut the power to the process. You are required to build a circuit to light a red warning LED if any of the following conditions arise:
• The power cut-off switch P is activated.
• Sensors 1 and Sensor 3 are activated at the same time but Sensor 2 and the power cut-off switch P are not activated.
• Sensors 2 and Sensor 3 are activated at the same time.
Present a truth table for this system.
5(b) Derive using Boolean algebra, a minimal sum-of-products function for this system.
5(c) Implement the circuit using logic gates (assume a maximum of 2-input gates are available).
5(d) Using De-Morgan's Theorem, convert the circuit output expression to a NOR gate only format and illustrate it (Assume that only 2-input NOR gates are available).
5(e) 4-bit binary-adder ICs typically have a carry-in input - why do you think this is the case? Briefly describe the problem of a ripple carry. If a 32-bit ripple carry adder was constructed as in the figure on page 3-54 (Full Adder Circuit Diagram - showing the internal gates) and the propagation delay of all logic gates is 8ms, what is the maximum safe clock frequency for operating such a device?
6(a) In your own words, distinguish between the following types of memory: ROM, PROM, EEPROM and RAM. Give examples of where EEPROMs and RAM might be used for in a home PC and other home devices/appliances.
6(b) In your own words, briefly explain the differences between:
(i) Simplex, half-duplex and full-duplex channels
(ii) Serial and parallel transmission
7(a) In your own words, describe the concept behind and advantages/disadvantages of each of Amplitude, Frequency and Phase Modulation. Describe a graph of the signal over time to help explain the differences.
7(b) A communication system employs a phase shift signalling technique that has four possible phase shifts. It has a signalling rate of 115200 baud, what is the information rate? If we upgrade the signalling technique to allow for eight possible phase shifts, what will the information rate be then?
8(a) If we have a stream of data consisting of binary 1s and 0s and the 1 occurs with three times the probability of the 0, calculate the information in a 1 and a 0.
8(b) Calculate the entropy of the data stream discussed in 8(a)
8(c) If the average time of a 1 and a 0 in this stream is 10ms, what is the average rate of information transmission?
9(a) How many miles apart can two communication stations be situated if they are linked by 22 gauge UTP cable, where the highest frequency signal is 1MHz and the maximum acceptable attenuation is 75dB? (See graph on page 5-4 of your notes).
9(b) If a 1.2/4.4 coaxial-pair tube (page 5-7 of your notes) is installed instead of the twisted- pair cable in 4(a), what distance can be achieved in miles if the signal has the form s = 50sin(2x106t) and the maximum acceptable attenuation remains at 75dB?
9(c) In your own words, describe the skin-effect that occurs at high frequencies in twisted pair cables. If at 1MHz the skin effect causes the effective radius of the cable to be reduced to half its value, what effect would this have on the resistance of the cable, compared to its DC resistance value?