23 Figure 3E. Light-emitting diode. IN ANSWERING QUESTIONS 3-36 AND 3-37, REFER TO FIGURE 3-E. 3-36.   When a negative voltage is applied to the proper cathodes in an LED display, a number is formed. To produce the numeral 5 on an LED display, which of the following diodes must have a negative potential on their cathodes?   1.    ABCDE   2.    ABGED   3.    AFGCD   4.    AFGBC 3-37.   If an LED segment has an "8" displayed and the negative bias is removed from diodes F and C, what numeral will be displayed?   1.    1   2.    2   3.    3   4. 4 3-38.   When replacing LED displays, which of the following methods should you use to ensure that the replacement display is of the same type as the faulty display?   1.    A visual inspection   2.    A check of the schematic symbols   3.    Both 1 and 2 above   4.    A check of the manufacturer's number 3-39.   The photodiode acts as what type of electronic device?   1.    Variable inductor   2.    Variable resistor   3.    Nonvariable inductor   4.    Nonvariable resistor 3-40.   When the photodiode is exposed to an external light, what happens to (a) resistance and (b) current? 1.    (a) Increase (b) decreases   2.    (a) Increases (b) increases   3.    (a) Decreases (b) increases   4.    (a) Decreases (b) decreases 3-41.   To conduct, how must a photodiode be biased? 1.    Reverse biased   2.    Forward biased   3.    Either 1 or 2 above, depending on light intensity 3-42.   Photodiodes are useful in which of the following applications?   1.    Computer card readers   2.    Photographic light meters   3.    Optic scanning equipment   4.    Each of the above 3-43.   Which of the following optoelectronic devices provides increased, conduction for a given light intensity?   1.    LED   2.    SCR   3.    Phototransistor   4.    Phototransformer 3-44.   To compensate for ambient light, a phototransistor must have a total number of how many leads?   1.    One   2.    Two   3.    Three   4.    Four