Questions: LED Circuits

Question 1

You connect an LED to a battery and it does not light up, but you know the battery is good. What is the most likely problem?

• A. The LED is burned out
• B. The wires are too thin
• C. The LED is connected backward — the positive and negative legs are reversed
• D. LEDs do not work with batteries

Answer: (C)

LEDs are diodes, which means they only allow current to flow in one direction. If the longer leg (positive, anode) is connected to the negative terminal and vice versa, no current flows and the LED stays dark. Flipping the LED should fix the problem immediately.

Question 2

An LED does not need a resistor because LEDs use very little power.

• T. True
• F. False

Answer: False

Even though LEDs use less power than traditional bulbs, they are very sensitive to excess current. Without a resistor to limit the current, an LED connected directly to a battery will draw too much current and burn out — sometimes in seconds. The resistor protects the LED by reducing current to a safe level.

Question 3

What makes an LED different from a regular light bulb?

Model answer: An LED only allows current to flow in one direction (it has polarity — a positive and negative leg), uses much less energy, produces less heat, and lasts much longer than a regular light bulb. Regular bulbs work with current in either direction and convert most of their energy to heat rather than light.

LEDs are fundamentally different components from incandescent bulbs. A bulb heats a wire filament until it glows — most energy becomes heat, not light. An LED produces light directly from electrical energy, wasting very little as heat. This efficiency is why LEDs have replaced bulbs in almost every application — from flashlights to stadium lights.