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Dad Field Manual · Field card 123 · Indoor & Rainy Day

Light a bulb: a kitchen-table battery circuit

Electricity feels like magic until your kid builds the loop that lights the bulb. In 45 minutes at the kitchen table you'll make a circuit, add a switch you build from a paper clip, and test which things in the junk drawer let the light come on.

Time
45 min
Cost
About $15
Ages
7 to 12
Where
Kitchen table

What you need

  • Two AA batteries and a 2-AA battery holder with wire leads
  • A small flashlight bulb (about 3 volts) in a mini screw-in holder
  • Three or four alligator-clip leads
  • Two brass paper fasteners, a metal paper clip and a scrap of cardboard
  • Test objects: spoon, foil, a coin, pencil, eraser, plastic lid
  • Electrical or masking tape

Before you start

  • No button or coin batteries, ever. A swallowed one can burn through a child's throat in as little as two hours. If you think one was swallowed, go to the ER now and call 1-800-222-1222.
  • AA batteries only, never the wall. This lab never touches outlets, extension cords or anything that plugs in. Say it out loud before you start.
  • Keep the bulb in the loop. A wire or metal object joining both battery ends with nothing between them can spark, smoke or start a fire. Feel something hot? Unclip it.
  • You handle any wire stripping. Clip leads mean no stripping. Afterward, take the batteries out and tape the ends of any you throw away.

Steps

  1. Light the bulb. Clip each battery lead to one side of the bulb holder. The full loop lights the bulb.
  2. Break the loop. Unclip one wire to show that any gap in the loop turns the light off.
  3. Build a paper-clip switch. Two brass fasteners in cardboard and a paper clip that swings between them make a switch.
  4. Test what conducts. With the bulb in the loop, touch two clip ends to each object. Sort: lights or doesn't.
  5. Draw the circuit. Draw the battery, wires, switch and bulb, then trace the loop with a finger.
  6. Shut it down. Open the switch, unclip everything, take the batteries out and pack it all away.

If it stalls

  • If the bulb won't light, check that it's screwed in snugly and that each clip is biting bare metal. Then try fresh batteries.
  • If you use an LED instead of a bulb, it only works one way round. If it stays dark, swap its two wires.
Objects tested · how many lit the bulb
Signed off: can do this.Signed by Date