Deck 20: Photodetectors

Question 1

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

Answer 1

True

Question 2

The most common photoconductive device is the ____________________.

Answer 2

cadmium sulfide cell,cad cell

Question 3

Figure 20-16
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What does the accompanying figure show?

Answer 3

The figure shows a photodetector used to detect the presence of an object on the conveyor line. When the object passes between the transmitter and receiver units, the light beam is broken and the detector activates.

Question 4

Figure 20-05
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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?

Question 5

Figure 20-10
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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 6

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

Question 7

Photovoltaic devices are more often called ____________________.

Question 8

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

Question 9

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

Question 10

____________________ emit electrons when in the presence of light.

Question 11

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

Question 12

Photovoltaic cells cannot operate electrical equipment without external power.

Question 13

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 14

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

Question 15

Figure 20-01


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