### SCEN103 Final Exam

#### May 26, 1999

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

1. (1 pt.)
Using a simple model of electronic band structure, explain why a metal is a good electrical conductor and an insulator is not.

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. (1 pt.)
What are the chief differences between a AA cell and a D cell?

5. (1 pt.)
Why is alternating current (ac) more widely used than direct current (dc) for distribution of electrical power?

6. (2 pts.)
At a SETI station (Search for Extra-Terrestrial Intelligence), the following binary signal repeatedly appears in the radio-frequency region of the electromagnetic spectrum. An alert computer operator notices that the message appears to be in ASCII. What does the message say? -- translate!

```0111  0011    0110  0101    0110  1100    0111  0101
0101  0010     0011  0011     0011  0000     0011  0001

__ __ __ __ __ __ __ __
```

Encode the following message for transmission in an intelligible form to the remote source:

CMOS2!

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

7. (2 pts.)

Complete the truth table below for the above gate combination.

A B C D E
0 0     1
0 1     0
1 0     0
1 1     0

What two-input gate should be used in the rectangular box (??) above to generate the desired truth table, where the output E is true when A and B are both false?

8. (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 eight 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).

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

Which 3-input logic gate does the circuit represent?

9. (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?

10. (2 pts.)
What value must R have to produce 10 A current through the battery?

11. (1 pt.)
MP3 is a relatively new audio file format where the file size is compressed and relatively small. Typically 1 Mb is equal to one minute of music, thus about one hour of music can be stored on a 64Mb Flash RAM. How many minutes of music could be stored in 64Mb for the uncompressed CD format?

12. (2 pts.)
Answer one of the following questions (part a, b, or c).

1. What is the difference between active and passive night vision aids? Which works better at long distances?
2. Compare the frame rate and resolution of HDTV vs. NTSC. Why was the 4:3 aspect ratio of NTSC originally adopted?
3. What are the main differences between polar orbiting satellites and geostationary satellites? What are their main applications?

"http://www.physics.udel.edu/~watson/scen103/99s/exams/final99spr.html"
Last updated May 26, 1999.
Copyright George Watson, Univ. of Delaware, 1999.