### SCEN167 Final Exam

#### May 20, 1996

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.

I found the note card to be

• essential
• useful
• of no assistance

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
. . (on/off) (on/off) (on/off) (on/off) HI/LO
LO LO . . . . .
LO HI . . . . .
HI LO . . . . .
HI HI . . . . .

 in n- p- LO off on HI on off

Describe how the bits of information are stored on the CD.

(What distinguishes the 0's from the 1's?) (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. (2 pts.)

What does the circuit accomplish? (What does it do? -- in words!) (1 pt.)

(HINT: the two gates enclosed in the shaded box comprise a half-adder.)

Please label drawing above and columns below as needed to work out the truth table.

C' A B . . . . C S
0 0 0 . . . . . .
0 0 1 . . . . . .
0 1 0 . . . . . .
0 1 1 . . . . . .
1 0 0 . . . . . .
1 0 1 . . . . . .
1 1 0 . . . . . .
1 1 1 . . . . . .

Consider the circuit below, comprised of a 6.0 V battery and two resistors, 15 ohm and 25 ohm.

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

b. What is the voltage across the 25 ohm resistor? (1 pt.)

c. What is the power dissipated by the 15 ohm resistor? (1 pt.)

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

On Tuesday May 14, most of the Delmarva peninsula south of Smyrna lost its electrical service because of inadvertent tripping of high voltage circuit breakers at the Keeney Extra High Voltage Substation near Glasgow. These breakers follow the transformers that lower the voltage from 500 kV, the level at which the electrical power is brought across the Delaware river from the Hope Creek power plant, to the 230 kV level used to distribute the power throughout the peninsula.

Assume that service was disrupted to 300,000 residents, with average demand of 1200 W each. Calculate the minimum current rating needed for the breakers operating at 230 kV. (1 pt.)

 From Fall 1995 Exam: 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? ``` 0101 0011 0110 0101 0110 1110 0110 0100 0010 0100 0010 0100 ``` Answer: Send\$\$

As a follow-up question this term, please compose the return signal: 2Broke
Use ASCII representation of characters and write out as a binary sequence. (2 pts.)

```
....  ....   ....  ....   ....  ....   ....  ....   ....  ....   ....  ....

```

Explain how the Copper-Top Tester for the AA battery works by using simple circuit concepts and Ohm's law. (2 pts.)

TOP

"http://www.physics.udel.edu/~watson/scen103/final96spr.html"
Last updated Dec. 9, 1996.
Copyright George Watson, Univ. of Delaware, 1996.