What Is A Circuit?
  
What do flashlights, digital clocks, and your portable pocket stereo all have in common? They all run on electricity! But in order for electricity to do its thing, it must travel through a circuit. You can think of a circuit as a pathway through which electricity can travel. Circuits can be as simple as the one that lights your night-light, or as complex as the latest computer chip — but they all work in the same general way.

In order for a circuit to function properly, the electricity must leave one end of the power source and return to the opposite end in an unbroken loop, or “circle.” In the case of a battery, the electricity leaves the negative (-) end and returns to the positive (+) end. In a wall outlet, there is also a positive end and a negative end — the two holes into which the two prongs of a plug fit. In the early days of electricity, when Thomas Edison was busy working on his light bulb , all circuits were simple and generally followed a straight-line path. These types of circuits are known as series circuits, and are the same systems used by most holiday tree lights. Many circuits can get really complicated. There are parallel, switched, integrated, and fused circuits. But no matter how you stack it, circuits are still a circle of electricity!

SCIENCE LAB ON CIRCUITS
Here’s what you’ll need:
• 2 “D” cells
• 3 pieces of aluminum foil cut into strips 6 inches long by 1/4 inch wide
• 2 standard flashlight bulbs
• A roll of cellophane tape

     Here’s what to do:
     Hook up a single battery to a bulb using the aluminum foil strips:
     1. Tape one strip of foil to the positive (+) end of the battery and a second strip to the negative (-) end of the battery.
     2. Touch the free end of the positive (+) strip to the metal side of the bulb right below the glass and the free end of the negative (-) strip to the little silver tip at the bottom of the bulb.

At this point, the bulb should light! Now you’re ready for the challenge.
    

1. What will happen to the brightness of the bulb when you add the second battery to the circuit? Try it yourself! How must the second battery be turned in order to get the bulb to light?

2. What happens to the brightness of the bulb when you add a second bulb to the circuit? Once you’ve got your results with the two batteries and the single bulb, use the third foil strip to insert the second bulb in the circuit. What happens to the brightness of the bulb now? Why do you think the change occurred? What happens to the bulbs if any of the connections in the circuit break?

Before you try this Science Lab, predict with your classmates what will happen to the brightness of the bulb when you hook up the second battery. Also, make sure you explain HOW the battery must be inserted into the circuit in order to get the bulb to light up. Then, predict what will happen when you add the second bulb to the circuit.