Science of Technology

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====== Staircase Switches ======

Lights over a staircase often have a switch at the top and the bottom of a staircase, so you could turn the light on when you need to see the steps and turn it off when you get to the other level.  The next three diagrams show possible wiring connections for two switches controlling one light.  The switches in these diagrams have a metal lever that can be flipped up or down.  The light will turn on when a pathway is created for the electricity to flow from one end of the battery through the light bulb and back to the other end of the battery.  The light will turn off when the pathway is broken.

Study these lighting diagrams and make a prediction about whether the light will be on or off when the switches are flipped up or down.  (You can use an online simulation of these switches at [[https://www.scienceoftech.net/FriendshipDetector/ThreeWaySwitch.html|this site]].)
{{ :fd:staircase-switches-series.png?400 |}}
|| Basement Switch || Kitchen Switch || Result (On/Off) ||
|| Up || Up || ?? ||
|| Up || Down || ?? ||
|| Down || Up || ?? ||
|| Down || Down || ?? ||

----

{{ :fd:staircase-switches-parallel.png?400 |}}
|| Basement Switch || Kitchen Switch || Result (On/Off) ||
|| Up || Up || ?? ||
|| Up || Down || ?? ||
|| Down || Up || ?? ||
|| Down || Down || ?? ||

----

{{ :fd:staircase-switches-three-way.png?400 |}}
|| Basement Switch || Kitchen Switch || Result (On/Off) ||
|| Up || Up || ?? ||
|| Up || Down || ?? ||
|| Down || Up || ?? ||
|| Down || Down || ?? ||

----

  * If the light is currently off, which house has more ways to turn the light on?
  * If the light is currently on, which house has more ways to turn the light off?
  * Imagine that you are in the kitchen and the lights are off.  You flip the switch, but the lights don’t come on.  You then have to run downstairs in the dark, flip that switch and then the lights go on.  But you had to go downstairs in the dark!  Which house has the kind of wiring that fits this scenario?  How did you know?
  * Imagine that you are in the kitchen and the lights are on.  You flip the switch, but the lights don’t turn off.  You then have to run downstairs, flip that switch and then the lights go off.  But you have to come back upstairs in the dark!  Which house has the kind of wiring that fits this scenario?  How did you know?
  * If you labeled “Up” as “OFF” and “Down” as “ON”, why would House C’s labels be frustrating?
Science of Technology

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