- Slides: 23
What is Static Electricity?
Static Electricity is… A stationary build-up of electric charge (electrons) on a material n Electricity that does not move (static vs. dynamic) n Shocking! n n http: //www. youtube. com/watch? v=6 Bk 8 Bn yjsoo
Laws of Static Charge 1. Opposite Charges Attract 2. Like Charges Repel 3. A charged object attracts an electrically neutral object!
Types of Charges Most objects are neutral – electrically uncharged n If 2 neutral objects are rubbed together, one becomes positively charged (loses electrons) and the other becomes negatively charged (gains electrons) n Direction of electron flow called the “ELECTROSTATIC SERIES” n
The Electrostatic Series n n n n Acetate Glass Wool Fur/Hair Ca, Mg, Pb Silk Aluminum Zinc Cotton Paraffin wax Ebonite Plastic C, Ni, Cu Sulfur Gold, Platinum Weak hold on electrons Strong hold on electrons
The Electrostatic Series n n n n Acetate Glass Wool Fur/Hair Ca, Mg, Pb Silk Aluminum Zinc Cotton Paraffin wax Ebonite Plastic C, Ni, Cu Sulfur Gold, Platinum For example: A plastic comb is rubbed with wool • The wool gives up electrons (weaker hold); becomes positively charged • The plastic comb takes electrons and becomes negatively charged
Let’s try another one… n n n n Acetate Glass Wool Fur/Hair Ca, Mg, Pb Silk Aluminum Zinc Cotton Paraffin wax Ebonite Plastic C, Ni, Cu Sulfur Gold, Platinum Your wool sweater rubs against your cotton T-shirt… Negative charge: • Cotton (gained electrons) Positive charge: • Wool (lost electrons)
How to put static charge on an object n n 1. Friction Between any two materials Rubbing it with something
How to put static charge on an object 2. By Contact n Touch something with a charged object n Positively charged object will take some electrons from neutral object, making it positive too n Negatively charged object will give electrons to the neutral object, making it negative too
Charging by Contact n n Conduction When 2 objects with different amounts of charge come into contact Electrons move from one object to the other
Lab Time! n Make your own electroscope!
How to put static charge on an object 3. By Induction n Bring a charged object near a neutral object without touching it
Charging objects Temporarily by Induction Bringing a charged rod near the electroscope will INDUCE the same charge on the silver leaf n Negative rod forces electrons down and makes the leaf negative n Positive rod attracts electrons up and makes the leaf positive n
Charging Objects Permanently by Induction
Controlling Static Electricity GROUNDING: n n Grounding a conductor means to connect it, through some conduction material to the ground (Earth). Although Earth is not an excellent conductor, it is so huge that it can accept or give up many electrons without significant change in its charge.
Grounding n A process that removes excess charge from an object.
Objects that need to be grounded! Appliances – to prevent dangerous shocks n Computers – sensitive to electrical surges n Fuel Tanker Trucks – prevent explosions! n http: //www. youtube. com/watch? v=tu. Zx. FL 9 c. Gk. I
Lightning (p. 493) n n n Negative charges on the bottom of the clouds repel electrons on the surface of the Earth, leaving the ground positively charged. The strong attraction between the negative cloud and the positive ground pull electrons off atoms and molecules (water, ice, etc. ) in the air. Once a chain of ions (an atom that has gained or lost electrons) forms, a gigantic discharge occurs between the cloud and the ground. The temperature of the air near a lightning bolt can reach as high as 33000 degrees Celsius, several times hotter than the sun’s surface. If the lightning hits a person, the electrical activity can stop the heart or respiration (breathing), nearly always
Struck by Lightning? n http: //www. youtube. com/watch? v=L 1 Hh. R AUq. Fq. M
Lightning Rods (p. 495) n n A lightning rod is charged by Induction, just like on the sphere of the electroscope, when you brought a negatively charged rod near it. The positively charged lightning rod is the highest point in the area. When a lightning bolt strikes, it hits the lightning rod. The electrons are carried around the building and into the ground by a heavy conductor, often made of braided copper wire.