Deck 20: Photodetectors

Question 1

Photo-operated devices fall into one of three categories. What are the categories?

Answer 1

Photo-operated devices fall into one of three categories: photovoltaic, photoemissive, and photoconductive.

Question 2

The most common photoconductive device is the ____________________.

Answer 2

cadmium sulfide cell
cad cell

Question 3

Photodetectors have to make physical contact with the object they are sensing.

Answer 3

False

Question 4

The amount of voltage produced by a cell is determined by the material of which it is made.

Question 5

Photoconductive devices exhibit a change of resistance due to the presence or absence of light.

Question 6

Photodetectors that have both the transmitter and the receiver units mounted in the same housing depend on a reflector for operation.

Question 7

Figure 20-12
What does the accompanying figure show?

Question 8

Figure 20-09
In the circuit shown in the accompanying figure, although the circuit will work if the cad cell is large enough to handle the current, there are still two problems. What are they?

Question 9

Photovoltaic cells cannot operate electrical equipment without external power.

Question 10

A(n) ____________________ steals the base current away from some other transistor to keep it turned off.

Question 11

Photovoltaic devices are more often called ____________________.

Question 12

Regardless of the type of photoemissive device used, or the type circuit it is used in, the greatest advantage of the photoemissive device is ____________________.

Question 13

____________________ emit electrons when in the presence of light.

Question 14

Figure 20-01
The accompanying figure shows the schematic symbol for a photovoltaic cell. What do the battery and arrow symbols mean?

Question 15

Figure 20-04
The circuit in the accompanying figure shows a phototransistor used to turn on a relay coil. What is the difference when the phototransistor is in the presence of darkness versus light?