Static Electricity Test Notes

Electrostatics--the study of static electricity

Static electricity is created when two different materials come into contact with one another...rubbing them together makes electrons move easier.  The electrons will move from one material to the other according to the placement of the materials on the triboelectric series.  Items at the top of the series hold their electrons loosely and will give up electrons (leaving them positive)  to materials lower than them on the series.  Items in a lower position on the triboelectric series hold onto their electrons tightly and will accept electrons from materials above them on the scale (making the lower position material negative)  

 

Insulators allow static charges to sit on their surface.  Conductors allow electrons to flow along them in a current.

Electrons are negativeProtons are positive.  Protons do not move from one material to another.  Protons are large and heavy and in the nucleus of the atom.  Electrons are small and lightweight and are already moving freely around the nucleus of the atom so they move easily from one material to another (following the rules of triboelectric series)

You can statically charge items two ways:

1) Charge by contact...the items must touch.  One material touches another and electrons are transferred.

2) Charge by induction...no touching.  A charged object is brought near, but not touching an uncharged object.  Electrons on the uncharged object will either move toward the charged object (if it is positively charged) or away from the charged object (if it is negatively charged).  This places a temporary charge on the previously uncharged object which will remain as long as the charged object is near it.                Electroscopes can show electron movement.  They have metal spheres on top, a metal shaft, and metal foils.  The metal is a conductor and allows electrons to flow through them in response to a charged object being brought nearby. 

Text Box: This shows an ebonite rod (-) held near an electroscope.  The foils on the electroscope will repel because electrons will repel the negative charge of the rod and be pushed down the shaft to the foils making them have a negative charge.  Since the foils are charged the same, they repel.  The sphere of the electroscope will have a positive charge while the ebonite rod is near it.
 
                                        

 

Text Box: This shows a glass rod (+) held near an electroscope.  The foils of the electroscope will repel because electrons on the electroscope will be attracted to the positive charge of the rod and be pulled up the shaft to the sphere of the electroscope.  This makes a negative charge at the top of the electroscope and a positive charge on the two foils.  Since the foils are charged the same, they repel.

   -  

 

 

        

      +   

 

 

 

You can use an electroscope and an object with a known charge (like an ebonite rod...we charge them to be negative) to find out the charge of any charged object.  Bring your object of known charge near the electroscope...the foils will repel.  If you bring an object with an unknown charge on it near the electroscope while still holding the ebonite rod near the electroscope, you will see some reaction with the foils.  If the foils repel even futher, the object with the unknown charge is negative...it has pushed even more electrons down the shaft making the foils react more strongly. 

If the foils close, even a little bit, the object with the unknown charge is positive.  It has attracted some of the electrons back up the shaft.

Grounding

To ground a charge means to release the charge to the ground where it can be spread out away from the charged object.  Lightning rods do this when they are hit by lightning.  The lightning hits the rod and travels down the wire attached to the rod into the ground. We used our hands/fingers to ground an electroscope. 

Remember:

Like charges repel, opposite charges attract.

Charged objects attract uncharged objects.