Correct Option
The correct option is (c) 2 and 3 only.
Explanation
A Light Emitting Diode (LED) is a semiconductor device that emits light when an electric current passes through it. It functions as a PN junction diode operating under forward bias. LEDs are particularly useful in electric testers because of their ability to function with very low voltage and current inputs compared to traditional filament bulbs.
Statement-wise Analysis
- Statement 1 is Incorrect: LEDs require very low current to glow. Standard filament bulbs rely on the heating effect of electric current (Joule heating) to emit light, which requires a much higher current. LEDs are used in testers specifically because they can detect and indicate the presence of very weak electric currents.
- Statement 2 is Correct: An LED is a polarity-sensitive device, typically identified by leads of unequal length. The longer lead corresponds to the Anode (positive side) and must be connected to the positive terminal of the battery or source.
- Statement 3 is Correct: The shorter lead corresponds to the Cathode (negative side) and must be connected to the negative terminal of the battery. If the polarity is reversed (reverse bias), the LED acts as an open switch and does not glow.
Key Takeaway: LEDs are efficient optoelectronic devices that glow with weak currents. They must be connected with the correct polarity: the longer lead (Anode) to the positive terminal and the shorter lead (Cathode) to the negative terminal.