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The Three Light Switches Puzzle Explained Step by Step

Problem Statement

You are standing outside a closed room. Inside the room is a single light bulb. Outside the room are three switches: - One switch controls the light bulb. - The other two switches do nothing. You may manipulate the switches as much as you like, but you may enter the room only once. How can you determine which switch controls the light bulb?

Answer

Use heat to identify the correct switch.

Step-by-Step Explanation

  1. 1

    Turn Switch 1 ON and leave it on for several minutes.

  2. 2

    Turn Switch 1 OFF, then immediately turn Switch 2 ON.

  3. 3

    Enter the room and observe the light bulb:

  4. 4

    If the bulb is on, Switch 2 controls it.

  5. 5

    If the bulb is off but warm, Switch 1 controls it.

  6. 6

    If the bulb is off and cold, Switch 3 controls it.

  7. 7

    This works because light bulbs produce heat when turned on. Even after being turned off, a bulb remains warm for a short time.

  8. 8

    By using both light and heat, you gain two pieces of information from a single visit.

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