chapter 8

Question 1

What does LED stand for?

Answer 1

Light-emitting diode

Question 2

An LED generates lights because the ? in its atoms of certain materials is of the frequencies of visible light.

Answer 2

radiation

Question 3

An LED will only generate light when it is reverse biased.

Answer 3

false

Question 4

A multicolor LED is constructed with two LEDs of different colors in one package. The LEDs are connected in reverse parallel. The ? decides which LED glows.

Answer 4

polarity

Question 5

? release energy that is below the visible light band and are commonly used in home electronics, such as remote controls.

Answer 5

Infrared-emitting diodes (IRED)

Question 6

LEDs and IREDs have a higher forward voltage drop than silicon diodes, usually around ? to ? .

Answer 6

1.2 V / 2.5 V

Question 7

“Laser” stands for Light Amplification by Stimulated Emission of Radiation

Answer 7

true

Question 8

With an incoherent light source, most of the waves are in-phase; in a laser source, the waves are out of phase.

Answer 8

false

Question 9

? are used in communications where high optical energy is required to pass through lengthy fiber optic cables.

Answer 9

laser diodes

Question 10

Which of the following is not a disadvantage of laser diodes over LEDs?

Answer 10

They require a fast switching power supply.

these are:

Their life expectancy is 10 times less than LEDs.

They cost 10 times more than LEDs.

They require elaborate power supplies.

Question 11

? are silicon devices that are sensitive to light.

Answer 11

Photodiodes

Question 12

Photodiodes can operate in ? mode.

Answer 12

photoconductive/photovoltaic

Question 13

The photodiode generates a voltage in response to light when in ? mode.

Answer 13

photovoltaic

Question 14

The conductance of the diode changes when light is applied when in ? mode.

Answer 14

photoconductive

Question 15

A photodiode in photovoltaic mode is reverse biased. A photodiode in photoconductive mode is forward biased.

Answer 15

false

Question 16

Optocouplers, also called optoisolators, couple the light from a light-emitting device with a light-sensitive device.

Answer 16

true

Question 17

Optocouplers optically couple a signal between two electrically isolated points.

Answer 17

true

Optocouplers are commonly used within PLC I/O cards. The optocoupler provides conversion between 120 VAC field devices and 5 VDC processor logic control. Optocouplers are also used in building automation systems I/O devices, such as, for example, LonWorks.

Question 18

Similar to the photodiode in photoconductive mode, the ? changes its resistance when exposed to light changes.

Answer 18

photoresistor