[logo] SCEN103 Final Exam

Feb. 5, 1998

For full credit, work must be shown, including formulas used and algebraic and numerical steps. Answers must include units.

1. (1 pt.)
From the Dec. 18, 1996 New York Times article "Drafting an Alphabet for the Digital Tradition":

Unicode is a fairly simple system that builds on the 128 characters of the 7-bit American Standard Code for Information Interchange (ASCII) and 256 characters of Latin-1, an 8-bit system also known as ISO 8859-1.

With 16 bits, Unicode is capable of encoding up to ______ characters, which is enough to represent most modern scripts.

Fill in the blank with the correct number. Show work below!

2. (1 pt.)
Explain photoconductivity using a band structure model of semiconductors. Include a sketch. (Your explanation shoud make it clear why silicon photoconducts but diamond does not.)

3. (1 pt.)
How is photoconductivity used in xerography, the process behind photocopying?

4. (2 pt.)
Discuss how "scratch resistance" is accomplished in the design of the compact disk. (A drawing would be nice...)

5. (2 pts.)
You did not respond favorably to the exercise where I asked you to estimate the storage capacity of a CD given the area spanned by 2 bits. Let's try a related calculation:

How many paving bricks would it take to cover the University of Delaware?


  1. As of September 1997, UD owned 2551 acres of land.
  2. There are 4840 square yards in an acre.
  3. A standard paving brick is 4" by 8".
[CD micrograph]

6. (3 pts.)
Construct the truth table for the combination of transistor switches shown below by indicating the on/off state of each transistor and the final output state for the four different input possibilities.
(Remember that n-channel MOSFETs are turned on by application of a positive voltage (HI); p-channel MOSFETs by application of ground (LO).

[4 switches for OR]

A B 1 2 3 4 C 5 6 D
    on/off   on/off  
LO LO                
LO HI                
HI LO                
HI HI                

Which common logic gate does the circuit represent?

7. (2 pts.)
Electrons and nuclei compose atoms and atoms compose molecules. Molecules compose our bodies.

Is our mass primarily electronic or nuclear?

Is our size primarily electronic or nuclear?

8. (4 pts.)
Consider the circuit below, consisting of a 9.0 V battery and two resistors, 12 ohm and 9 ohm.

[Circuit schematic]

a. What is the voltage across the 12 ohm resistor?

b. What is the current through the 9 ohm resistor?

c. What is the power dissipated by the 12 ohm resistor?

d. What is the power provided by the battery?

9. (2 pts.)
At a SETI station (Search for Extra-Terrestrial Intelligence), the following binary signal repeatedly appears in the microwave region of the electromagnetic spectrum. An alert computer operator notices that the message has a meaning if decoded using an ASCII table. What does the message say? (2 pts.)

0100 1000    0110 0101    0110 1100    0111 0000    0010 0001    0011 1111

10. (2 pts.)
[Schematic of XOR gate]

Using the attached truth tables, construct the truth table for this combination of gates.

0 0      
0 1      
1 0      
1 1      

What logic operation does this circuit accomplish?
(Under what conditions is the output TRUE?)

Last updated Feb. 6, 1998.
Copyright George Watson, Univ. of Delaware, 1996.