© 2019 by Pernille Dahl & Cole Robbins. 

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Christmas Light Circuit

Parts needed:
  • 2 Model

  • 1 Baseboard

  • 1-3 Christmas lights, in series

  • File folders or stiff paper

  • 2 Film cans or wood blocks

  • 1/2 Paint paddle

  • 1 Popsicle stick

  • 3 Wires, 8”

  • 1 Weight (nut or bolt)

  • 1 Battery, 9 volt

  •  

  • Battery snap OR two small paper clips

Extra Tools: 
  • Philips screwdriver (to make holes for lights)

  • Black tape

  • Markers and other decorations

Decoration
  • Colored paper, glue and glitter, tinsel

Project Description:

Wire is the conductor in which the electricity travels in this circuit.  Air, on the other hand, is a pretty good insulator so when the weight is swinging between its contacts electricity does not travel in the circuit.  This is known as an open circuit, and is exactly what is happening in a light switch when you shut off the light. 

 

When the wire holding the weight hits the loop wire, the circuit is complete and electricity can travel through it.  The lights glow.  If you happen to cross the two bare ends of one of the Christmas tree lights, the light will go out but the battery will continue pushing electricity around a circuit.  This circuit is smaller, that is, shorter than the one you had before you touched the wires.  It is thus called a short circuit. 

 

The light that went out when you shorted it had some resistance, which limited the amount of electricity that could flow.  When the circuit is shorted this resistance is gone, and much more electricity can travel around the circuit.  In our project the worst that will happen with such a short circuit is that the battery will get warm and go dead rapidly.  However, if the battery was much bigger and could supply a lot of electricity, this would be a dangerous situation.  The wires or other components of the circuit could become hot and maybe explode.  This is why homes have fuses or circuit breakers.  Both of these instruments open a circuit that suddenly has too much electricity traveling in it, usually due to a short circuit. 

 

Try taking one light bulb out of its socket.  If the other one goes out, you have them wired in series, that is, one in line with the other.  If the other continues to glow, you have them wired in parallel, that is, one across the other.  Each type of circuit has its advantages.  Parallel bulbs will each stay lit regardless of what happens to the other, and they’ll glow more brightly because they each get the full voltage of the battery.  On the other hand, they’ll be using more electricity.  Bulbs in series have to share the total voltage of the circuit.  For this reason, we can use these light bulbs with a nine-volt battery when they were designed to be used with a 120-volt wall outlet.  We only use two or three, whereas in their original circuit, there were perhaps 50 bulbs sharing the 120 volts. 

 

In general, if you have fewer lights in a circuit, each will shine brighter. Each additional light adds more resistance that results in less electricity flowing.  To get them to blink faster, you’d need a shorter pendulum on the switch.  A heavier weight would help them to continue blinking longer.   

How we Built it:

Glue one film can in the middle of one edge of the baseboard.   Cut about 9” of the paint paddle.  Glue the Popsicle stick to the paint paddle.

 

Glue the other end of the paint paddle to the edge of the wood base and also to the film can.  Glue the other film can on the opposite edge of the baseboard. 

 

Strip both ends of three wires.   Strip both ends of the Christmas lights.  Connect one wire to each end of the Christmas light wires.  One of the Christmas light wires will go straight to the battery, the other to the Popsicle stick. 

  

Drape one wire over the Popsicle stick and wrap it around once.  Tie the weight to this wire near the bottom.  Wrap the third wire around the paint paddle and make a loop that encompasses the hanging wire.  This wire will go straight to the battery.  These two wires need to be stripped about 5” from one end.  When the hanging wire swings, it needs to contact the loop wire. 

Put a battery in the film can near the paint paddle. Use a 9-volt battery snap if you have one, or connect one paper clip to the loop wire and one to the wire coming from the lights.   Connect the paperclips to the battery snaps taking care not to let them touch together.  There should be a single series circuit: from one side of the battery, to the Christmas lights, to the swinging wire, to the loop of wire, and back to the battery. 

   

Draw a picture on the file folder or thin cardboard and cut it out.  Make the holes with the screwdriver. Each hole must be big enough to hold the light firmly. Insert the lights and glue them in place if they do not stay by themselves.

 

Glue the figure to the front film can. Add Popsicle sticks if it does not stand up.  Swing the weight back and forth. The lights will flash every time the dangling wire touches the loop completing the circuit.

 

Concepts:

  1. Electricity has to have a complete in order to travel from one side of the battery to the other. This path is called a circuit.

  2. A switch breaks – or “opens” – the circuit and stops the electricity flowing.

  3. The battery “pushes” the electricity around the circuit.  When the chemical reaction within the battery runs out of chemicals, the battery is dead and can’t push any more.

Questions:

  1. What happens when one light goes out?

  2. If you had fewer lights, would they be brighter or dimmer?

  3. How could you make it blink longer?

  4. How could you make it blink faster?