You found that electrons travel around the nucleus of an atom and are held in their orbits by the attraction of the positive charge in the nucleus . If you could somehow force an electron out of its orbit , then the electron's action would become what is known as electricity . Electrons which are forced out of their orbits in some way will leave a lack of electrons in the material which they leave and will cause an ex- cess of electrons to exist at the point where they come to rest .
This ex- cess of electrons in one material is called a " negative " charge while the lack of electrons in the other material is called a " positive " charge . When these charges exist you have what is called " static " electricity . To cause either a " positive " or " negative " charge , the electron must be moved while the positive charges in the nucleus do not move . Any material which has a " positive charge " will have its normal number of positive charges in the nucleus but will have electrons missing or lack- ing .
However , a material which is negatively charged actually has an excess of electrons . You are now ready to find out how friction can produce this excess or lack of electrons to cause static electricity .
1 Static Charges from Friction:-
You have studied the electron and the meaning of positive and negative charges , so that you are now ready to find out how these charges are pro- duced . The main source of static electricity which you will use is friction . If you should rub two different materials together , electrons may be forced out of their orbits in one material and captured in the other .
The material which captures electrons would then have a negative charge and the ma- terial which loses electrons would have a positive charge . When two materials rub together , due to friction contact , some electron orbits of the materials cross each other and one material may give up electrons to the other .
If this happens , static charges are built up in the two materials , and friction has thus been a source of electricity . The charge which you might cause to exist could be either positive or negative depending on which material gives up electrons more freely . Some materials which easily build up static electricity are glass , amber , hard rubber , waxes , flannel , silk , rayon and nylon .
When hard rubber is rubbed with fur , the fur loses electrons to the rod - the rod becomes neg- atively charged and the fur positively charged . When glass is rubbed with silk , the glass rod loses electrons - the rod becomes positively charged and the silk negatively charged . You will find out that a static charge may transfer from one material to another without friction , but the original source of these static charges is friction .
2 Attraction and Repulsion of Charges:-
When materials are charged with static electricity they behave in a manner different from normal . For instance , if you place a positively charged ball near one which is charged negatively , the balls will attract each other . If the charges are great enough and the balls are light and free to move , they -will come into contact . Whether they are free to move or not , a force of attraction always exists between unlike charges ..
This attraction takes place because the excess electrons of a negative charge are trying to find a place where extra electrons are needed . If you bring two materials of opposite charges together , the excess electrons of the negative charge will transfer to the material having a lack of electrons . This transfer or crossing over of electrons from a negative to a positive charge is called " discharge . " Using two balls with the same type of charge , either positive or negative , you would find that they repel each other .
3 Transfer of Static Charges:-
through Contact While most static charges are due to friction , you will find that they may also be caused by other means . If an object has a static charge , it will in- fluence all other nearby objects . This influence may be exerted through contact or induction . Positive charges mean a lack of electrons and always attract electrons , while negative charges mean an excess of electrons and always repel electrons .
If you should touch a positively charged rod to an uncharged metal bar , it will attract electrons in the bar to the point of contact . Some of these electrons will leave the bar and enter the rod , causing the bar to become positively charged and decreasing the positive charge of the rod .
By touching a negatively charged rod to the uncharged bar , you would cause the bar also to become negatively charged . As the negatively charged rod is brought near the uncharged bar , electrons in that portion of the bar nearest the rod would be repelled toward the side opposite the rod . The portion of the bar near the rod will then be charged positively and the opposite side will be charged negatively .
As the rod is touched to the bar , some of the excess electrons in the negatively charged rod will flow into the bar to neutralize the positive charge in that portion of the bar but the opposite side of the bar retains its negative charge . When the rod is lifted away from the bar , the negative charge remains in the bar and the rod is still negatively charged but has very few excess electrons . When a charged object touches an uncharged object , it loses some of its charge to the uncharged object until each has the same amount of charge .
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