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Complete Circuit: How Does a Flashlight Work? (page 2)

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Author: Erin Bjornsson

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D, AA, and AAA batteries will light the circuit. Two batteries will light the bulb brighter than one battery.

Why?

D, AA and AAA batteries all have the same voltage, so they will all provide enough current to light the bulb when the circuit is closed. D batteries are larger than AA batteries, and AA batteries are larger than AAA batteries. For batteries with the same voltage, a larger battery will have a longer life than a smaller battery. Using two batteries instead of one should have made the light shine brighter. This is because you provided more voltage to the circuit and thus more current. More current means more electrons are flowing into the filament. Subsequently, more energy is being emitted, or released, in the form of light.

When the circuit is closed (that is, when the bottom wire touches the negative terminal of the battery), current can flow through the circuit. When the wire is unconnected, current has nowhere to go. This is why the light does not turn on. It is important for the wire ends to be stripped so that the wire’s metal can be in contact with the battery’s metal. The coating on the wire is insulation and resists electron flow  and obstructs the circuit. This makes the coated wire safe to touch when current is flowing through it.

Light bulbs contain light-emitting wires called filaments. The bulbs may also be filled with different gasses which give off colors like neon. When current passes through the bulb, the filament gets hot and emits radiation in the form of light and heat. Old fashioned light bulbs typically get very hot and can be dangerous. Many bulbs in flashlights, decorative lights, and electronics are now LED bulbs, which are safer and more energy efficient.

You can try repeating this experiment with different kinds of small light bulbs, perhaps an LED light bulb, to see if you get different results.  

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