Electrical Circuits: Switch It!

Electrical Circuits: Switch It!

Contributed by Montu Ganesh


  • In an electrical circuit, what happens when I open and close a switch?
  • What happens when 2 light bulbs are connected in series with each other? What happens when one switch goes off in a series circuit?
  • What happens when 2 light bulbs are connected in parallel with each other? What happens when one switch goes off in a parallel circuit?


  • 2 1.5-Volt Lightbulbs (Better to have more)
  • Sockets for those lightbulbs
  • Electrical wire
  • D-Cell Battery
  • Tape
  • Aluminum Foil
  • Scissors


  1. Screw a 1.5-Volt light bulb into a socket and do the same for the second light bulb
  2. Tape an electrical wire to the bottom of the D-cell battery and tape another electrical wire to the top of the D-cell battery
  3. Prepare the foil:
    • Cut a strip of aluminum foil about 2 inches long and 1 inch wide
    • Fold the strip half way, then fold it one-third from the end
    • Cut another strip of aluminum foil 1 inch by 1 inch and fold it by half
    • Tape one end of each aluminum so the longer strip can make contact with shorter strip when laid flat on the table
  4. Take the other end of electrical wire taped to the bottom end of the battery, lay it under the end of the longer aluminum foil strip taped down, and tape the wire in place. Also:
    • Connect the end of the electrical wire taped to the top of the battery to one end of the socket for one 1.5-Volt lightbulb
    • Connect the electrical wire from the other end of the socket to underneath the shorter strip of aluminum foil, and tape it in place
  5. Now push the free end of the longer end of the aluminum foil so it makes contact with the shorter one, and watch the light bulb light up
  6. Connect a second lightbulb after screwing it to a socket, and connect it in the circuit with the other lightbulb and the shorter strip of aluminum foil using electrical wire
  7. Now lay the longer strip of aluminum foil flat to turn the switch on and see what happens to the two lightbulbs
  8. Revert back to the original circuit design, but this time, connect the light bulb to the second light bulb socket using electrical wires. These light bulbs are now in parallel with each other
  9. Place the long strip of foil on the shorter strip and now see what happens to the light bulbs

Physics Concepts and Questions

  • What caused the light bulb to light up when the strip of aluminum foil was placed down on the table?
  • Why were the two lightbulbs able to light up as such as well?
  • What caused the 2 light bulbs to light up differently when in series vs in parallel with each other
  • Ohm’s Law: V=IR
  • The D-Cell battery acts as a power supply, providing voltage for the circuit. This allows the charges to freely flow through
  • Conductivity of metals and flow of charge to form current: this is why the light bulb is able to light up when the metal strip is laid flat on the table as it provides a path for the free electrons to flow, forming the current

Resistance in series and resistance in parallel: there is greater resistance in series than in parallel, causing the light bulbs to have lower brightness in series than in parallel

Conclusions and Further Investigations

  • What would happen if we continued for 3 bulbs? What would happen if some were in series vs some in parallel?
    • The difference between series and parallel circuits would be shown clearly for 3 lightbulbs as well. The brightness of the light bulbs in parallel would be slightly increased



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