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Complete Circuit: How Does a Flashlight Work?

based on 44 ratings
Author: Erin Bjornsson

Electricity makes our lives easier by powering our lights, refrigerators, and even some cars! Electricity can travel around in systems called circuits, which carry current—a stream of flowing electrons.

Batteries are a form of stored electricity and can have different voltages, or levels of electric force. Research the types of batteries you will use in this experiment online to find out their voltages. Batteries provide direct current (DC) to a circuit, which means the direction of the current is always the same. Electrical outlets in our home provide alternating current (AC), which is more efficient at carrying electricity.

Circuits, which often use batteries and wires to power useful devices like light bulbs, carry current when they are in a closed circuit, which means that electricity can travel in a loop. Resistance, which is a property of a material, can be found in the batteries, wires, lights, and other devices and is what causes energy to be used up in a system.

Problem

How do we build a circuit to create a flashlight? How do different voltages affect the bulb’s brightness?

Materials

  • Flashlight that holds 2 size D batteries
  • 1-foot length of insulated (coated) wire
  • Wire stripper
  • Duct tape or electrical tape
  • 2 size D batteries
  • 2 size AA batteries
  • 2 size AAA batteries

Procedure

  1. Unscrew the top portion of the light bulb, removing the back half that contains the batteries.
  2. Have an adult help your strip 1.5 inches of insulation off both ends of the wire.
  3. Wrap one end of the bare wire around the metal part at the bottom of the bulb. Why do you think the wire need to be bare here?
  4. Coil up the other bare end of the wire into a spiral that can lie flat against the flat bottom of a battery
  5. To test each battery, first press the battery’s positive terminal against the bottom of the metal end of your light bulb.
  6. Next, press the coiled end of the wire to the negative terminal of the battery to close the circuit. Record your observations, making sure to note which type of battery you used and whether or not the light bulb lit upon closing the circuit. If it did, make a note of how bright it was, using words like “bright,” “normal” or “dim.”
  7. Tape two batteries of the same type together with duct tape or electrical tape. The positive terminal of one battery should be in contact with the negative terminal of the other.
  8. Repeat steps 5 and 6 with your double battery. Record your observations, making sure to note which type of battery you used, how many you used, and whether or not the light bulb lit upon closing the circuit. If it did, make a note of how bright it was, using words like “bright,” “normal” or “dim.” Does using more batteries make the light brighter?

Note: Do not increase the number of batteries. While the light might sometimes still illuminate, too much current flowing through the circuit can burn out the bulb. The batteries used in this experiment are low voltage and are the safest batteries to use.

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