L.R. Ingersoll Wonders of Physics Museum
UW–⁠Madison Department of Physics

Circuit Puzzle 1

On the board below is a drawing representing the circuit inside the box connecting the switches and light bulbs.

Wires are shown by LINES. Switches are shown by ANGLED LINES.

Light bulbs are represented at their location in the circuit by CIRCLES.

Things to keep in mind when trying to accomplish the tasks:

When a switch is open (OFF/ down) no electrons flow through that section of wire (no current).

Light bulbs have resistance to flowing charges, so the more of them there are (or the longer the section of wire, which also has some resistance), the dimmer the lights will be since less power will be available for the light bulbs. See the Series/Parallel Circuit Exhibit for another circuit puzzle!

Try to accomplish the following tasks by flipping the switches!!

  1. FLIP THE SWITCHES TO GET LIGHTS A AND C TO TURN ON, BUT NOT B.
    1. ANSWER: SW1 UP, SW2 UP, SW3 UP, SW4 DOWN, SW5 UP, SW6 DOWN
  1. FLIP THE SWITCHES TO GET JUST LIGHT B TO TURN ON.
    1. ANSWER: SW1 UP, SW2 DOWN, SW3 UP, SW4 UP, SW5 DOWN, SW6 DOWN
  1. FLIP THE SWITCHES TO GET JUST LIGHTS B AND C TO TURN ON.
    1. ANSWER 2 (dim): SW1 UP, SW2 DOWN, SW3 DOWN, SW4 DOWN, SW5 DOWN, SW6 DOWN
    2. ANSWER 2 (bright): SW1 UP, SW2 DOWN, SW3 UP, SW4 UP, SW5 UP, SW6 DOWN
  1. FLIP THE SWITCHES TO GET ALL THREE LIGHTS TO TURN ON.
    1. ANSWER1 (dim): SW1 UP, SW2 UP, SW3 UP, SW4 DOWN, SW5 DOWN, SW6 DOWN
    2. ANSWER2 (bright): SW1 UP, SW2 UP, SW3 UP, SW4 UP, SW5 UP, SW6 DOWN

V=IR   There is a set voltage from the battery so more resistance (longer wire or more lightbulbs) = less current

P=IV=I2R   Current gets split between each available path.  The amount of current in each path depends on the resistance of that path.  All the same light bulbs, so all have same resistance, but the current available depends on how much current is flowing through each section of wire.

 

Other Combinations:

  1. JUST Bulb “A”
    1. ANSWER: SW1 UP, SW2 UP, SW3 UP, SW4 DOWN, SW5 DOWN, SW6 UP
  1. All lights off
    1. ANSWER 1: SW1 DOWN, others don’t matter since no current in circuit
    2. ANSWER 2: SW1 UP, SW2 DOWN, SW3 DOWN, SW4 DOWN or UP, SW5 DOWN or UP, SW6 UP
    3. ANSWER 3: SW1 UP, SW2 UP, SW3 DOWN, SW4 DOWN, SW5 DOWN or UP, SW6 UP
  1. Just Bulb “C”
    1. ANSWER 2: SW1 UP, SW2 UP, SW3 DOWN, SW4 DOWN or UP, SW5 UP, SW6 UP

 

Physics Lecture Demonstration Database