1. 3to9.pdf
OSCAIL
Batchelor of Science (Hons) in Information Technology
Communications Technology 1
2013 Assignment 2 Questions
Answer All Questions
1(a) In your own words, explain the concepts of electromotive
force and potential
difference.
[2 marks]
1(b) In your own words, describe the concept of a magnetic
field.
[2 marks]
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.

2. 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.
[2 marks]
1(d) Examine the discussion at:
http://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?
[4 marks]
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

3. practice to run data cable alongside AC electrical cables over
long distances?
[3 marks]
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.
[3 marks]
[Q2 Contd. PTO]
http://en.wikipedia.org/wiki/War_of_Currents
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

4. 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).
Figure 2 - Two Diode Circuits
[4 marks]
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

5. how could we get an
equivalent behaviour using a different wiring configuration on
the input side for both
NAND and NOR gates?
[4 marks]
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.
[4 marks]
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.
[3 marks]
Illustrate the two equivalent
circuits.

6. [6 marks]
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).
[4 marks]
Question 5 [20 marks]
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:
-off switch P is activated.
Sensor 2 and the power

7. cut-off switch P are not activated.
Present a truth table for this system.
[3 marks]
5(b) Derive using Boolean algebra, a minimal sum-of-products
function for this system.
[4 marks]
5(c) Implement the circuit using logic gates (assume a
maximum of 2-input gates are
available).
[2 marks]
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 marks]
5(e) 4-bit binary-adder ICs typically have a carry-in input –
why do you think this is the

8. 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 marks]
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 marks]
6(b) In your own words, briefly explain the differences
between:
(i) Simplex, half-duplex and full-duplex channels
(ii) Serial and parallel transmission

9. [4 marks]
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.
[6 marks]
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?
[4 marks]
8(a) If we have a stream of data consisting of binary 1s and 0s
and the 1 occurs with three

10. times the probability of the 0, calculate the information in a 1
and a 0.
[4 marks]
8(b) Calculate the entropy of the data stream discussed in 8(a)
[3 marks]
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?
[3 marks]
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

11. notes).
[2 marks]
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(2x10
6
imum acceptable attenuation remains at 75dB?
[4 marks]
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?
[4 marks]
extra.docx

12. 2. 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
You may use Notepad++ or the HMTL Kit editor:
http://www.chami.com/html-kit/ or another editor of your
choice.
(40 marks)
(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)
Deliverables:
I. You should upload a zipped archive of all the files that make
up the web page (See appendix B below if you need help with
zipping files) i.e. one html page (with file extension .htm or
.html) and any images or other linked files or folders. Your
webpage should use relative addressing.
1) Two socks are randomly drawn, without replacement, from a
drawer containing 2 green sock, 3 black socks, and 4 red socks.

13. Let X be the number of green socks and let Y be the number of
black socks among the two socks that have been drawn.
a) Draw a two- way distribution table representing the joint
distribution of X and Y
b) Find a formula for the joint p.d.f f(x,y) of X and Y
c) Find the marginal distribution table of X and Y
d) Compute µx, µy, V(x), and V(y)
e) Compute E(X,Y) and the covariane between X an Y
f) Compute the value of the coefficient of linear correlation p
g) Find the conditional distribution table of Y, given X=1
h) Compute E(Y|1) and V(Y|1)
i) Are X and Y independent? Explain you answers.
2) Let the joint p.d.f. of X and Y be given by f(x,y) = c (x^2 +
Y^2, for x=-1, 0,1,3 and y = -1,2,3 where c is a constant.
a) Find the value of c
b) Find the conditional distribution table of X, given that Y=2
c) Compute P(X>2-Y)
d) Compute Cov(X,Y)