SCEN102 Final Exam

December 14, 1995

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

One 3" x 5" note card is permitted for this exam. Otherwise, the exam is closed book.

The note card must be turned in with the final exam.

Please check the most appropriate answer to the following statement:
I found the note card to be


Explain the difference between a semiconductor and an insulator using a model (drawing) of electronic band structure. (1 pt.)

What is the goal of doping a pure semiconductor? (1 pt.)

Construct the truth table for the combination of transistor switches below. (2 pts.)

What common logic gate does the circuit represent? (1 pt.)

A B 1 2 3 4 C
LO LO . . . . .
LO HI . . . . .
HI LO . . . . .
HI HI . . . . .

[4 transistor switches]

in n- p-
LO off on
HI on off


[CD micrograph]

Describe how the bits of information are stored on the CD.
(What distinguishes the 0's from the 1's?) (1 pt.)

Describe how the laser pickup works.
(How are the bits read from the disk?) (1 pt.)

Discuss how "scratch resistance" is accomplished in the design of the CD.
(A drawing would be nice...) (1 pt.)

If a typical printed page takes 3 kb (kilobytes) of storage, how many 10-page papers could be stored on a CD ROM? (1 pt.)


Work out the truth table for the following combination of gates. (1 pt.)
What does the circuit accomplish? (What does it do?) (1 pt.)

[2 logic gates]


Consider the circuit below, comprised of a 9.0 V battery and two resistors, 50 ohm and 25 ohm.

a. What is the current flowing in the circuit? (1 pt.)

b. What is the voltage across the 50 ohm resistor? (1 pt.)

c. What is the power dissipated by the 25 ohm resistor? (1 pt.)

d. What is the power delivered by the battery? (1 pt.)

[Circuit schematic]


Work out the truth table for the following combination of gates: (2 pts.)

[3 Gate combination]

A B C E F D
1 0 0 . . .
1 0 1 . . .
1 1 0 . . .
1 1 1 . . .
0 0 0 . . .
0 0 1 . . .
0 1 0 . . .
0 1 1 . . .


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.)

Refer to the ASCII table, as needed.

0101  0011    0110  0101    0110  1110    0110  0100    0010  0100    0010  0100

Explain how the Copper-Top Tester for the 9 V battery works by using simple circuit concepts and Ohm's law. (1 pt.)

Take a look at the scanned image.

(This was a group exercise during the semester -- Sept. 26)