Which of the following is true about a Light Emitting Diode (LED)?

• A. It can operate with both AC and DC
• B. It only emits light with a DC current
• C. It functions as a short circuit
• D. It acts as a power transformer

Answer: (B)

A Light Emitting Diode (LED) is a semiconductor device that emits light when an electric current passes through it. The fundamental operation of an LED relies on the flow of current in one direction, which is typical of diodes. This means that an LED requires direct current (DC) to function correctly. When DC is applied, the LED allows current to flow from the anode to the cathode, resulting in the emission of light.

Operating an LED with alternating current (AC) would be detrimental because the reverse bias that occurs in an AC circuit can damage the LED. Therefore, option B accurately describes the requirement for DC to emit light, making it the correct choice.

The other options mischaracterize LED functionality. An LED does not operate with both AC and DC safely; it certainly doesn't function as a short circuit since it has specific operational characteristics that prevent unrestricted current flow. Additionally, an LED does not act as a power transformer, which serves a different purpose in electrical circuits—transforming voltage levels rather than emitting light.