Key Topic 27: Light Emitting Diodes

Question 1

3-27C1: What type of bias is required for an LED to produce luminescence?

A. Reverse bias.
B. Forward bias.
C. Logic 0 (Lo) bias.
D. Logic 1 (Hi) bias.

Answer 1

B. Forward bias.

Question 2

3-27C2: What determines the visible color radiated by an LED junction?

A. The color of a lens in an eyepiece.
B. The amount of voltage across the device.
C. The amount of current through the device.
D. The materials used to construct the device.

Answer 2

D. The materials used to construct the device.

Question 3

3-27C3: What is the normal operating current of a light-emitting diode?

A. 20 mA.
B. 5 mA.
C. 10 mA.
D. 40 mA.

Answer 3

A. 20 mA.

Question 4

3-27C4: What would be the maximum current to safely illuminate an LED?

A. 1 amp.
B. 1 microamp.
C. 500 milliamps.
D. 20 mA.

Answer 4

D. 20 mA.

Question 5

3-27C5: An LED facing a photodiode in a light-tight enclosure is commonly known as a/an:

A. Optoisolator.
B. Seven segment LED.
C. Optointurrupter.
D. Infra-red (IR) detector.

Answer 5

A. Optoisolator.

Question 6

3-27C6: What circuit component must be connected in series to protect an LED?

A. Bypass capacitor to ground.
B. Electrolytic capacitor.
C. Series resistor.
D. Shunt coil in series.

Answer 6

C. Series resistor.