Remember… Static electricity happens when there is a build up of charges on the surface of an object. (Static means “not moving”
http://www.pbslearningmedia.org/resource/phy03.sci.phys.mfw.lightning/lightning/http://www.pbslearningmedia.org/resource/phy03.sci.phys.mfw.lightning/lightning/ • Describe Benjamin Franklin's experiment. What did it teach us about lightning? • What causes lightning? • Have you ever seen lightning? In which direction did you think it was traveling? What did you learn from the video about the direction in which lightning travels? • Electrical charge builds up in a cloud before we see lightning. Can you think of an example from your everyday life where an electric charge builds up in much the same way?
Background for lightning lab: PurposeTo observe the spark effect of static electricity. Materials copy of "Indoor Lightning" student handout (PDF or HTML) (below) A piece of notebook paper or a sheet of plastic, such as a transparency sheet Two or three flat pieces of metal, such as a 12" x 12" square of aluminum foil folded into a flat disc, the top of a metal can, or the bottom of an aluminum pie pan (Be careful with sharp edges.) A piece of wool cloth (mittens or pieces of a sweater work well) A stopwatch or a clock with a second hand
Procedure A lightning bolt is an enormous release of static electric charge. We commonly experience the phenomenon of small amounts of static electricity when removing clothes from the dryer, brushing our hair, or walking across a carpeted floor and then touching a metal doorknob. Most of the time the sparks from these static electric releases are not visible, so the connection between these experiences and lightning may not be evident to students. To demonstrate the spark effect of static electricity, have students try this activity. (This activity will be most successful on a very dry day or in winter.) Organize the students into pairs and give a set of materials to each team. If possible, darken the room to make the sparks more visible. Point out to the class that it takes a lot of physical energy to create enough of a charge to make a small, barely visible spark. This energy is insignificant compared to the amount of electric charge that builds up in a thundercloud.
Why it works…When students rub the wool piece on the paper, they build up a negative electric charge on the paper. The metal sheet also carries a negative charge. This negative charge is increased when the metal is placed on the paper. When the students' fingers touch the metal, the negative charge is attracted to the positive charge in their bodies and creates a spark. Lightning is formed in a similar manner. Under normal atmospheric conditions, the electrical charge of the ground is evenly balanced between positive and negative. The most frequent type of lightning occurs when a thundercloud has built up a strong negative charge. It repels the negative charge of the ground, causing the charge to be pushed down slightly, similar to the effect of holding two magnets so that their like charges repel each other. With the negative charge pushed down, the ground becomes more positively charged, creating an attractive force for the negative charge in the thundercloud. This same effect also occurs when students place the negatively charged metal on top of the negatively charged paper and then place their positively charged fingers near the negative charge.
Current Electricity Current electricity is when charges move through an object.
Conductors and Insulators Electricity cannot flow through all types of materials. Some materials block the path of electricity. Conductor – any material that electricity can flow through easily. Ex: metals, water, people Insulator – any material that electricity cannot flow through. Ex: rubber, plastic, glass, wood
Electrical cords on devices are covered in plastic. The metal wire inside is often made of copper, which is an excellent conductor. Electricity flows through the wire, but not through the plastic, so that you can touch the cord. This is why electricians wear thick rubber gloves. Interesting… A finger can operate a touch screen. A tiny amount of electric charge in the touch screen moves into the finger. This tells the device where the finger is pointing. What happens when you wear gloves?