Electrostatics

Electrostatics

1. Electrostatics is the study of electric charge which is at rest or static (not moving).

2. Two types of charge

   • Positive charge
     • Is carried by protons. If there are more positive than negative charges, then the object is positively charged.
       • • 8 positive charges 6 negative charges: 8+ (-6) = 2
           • The net charge is +2. This means that the object is positively charged.
       • Electrons are removed making the object electron deficient.
   • Negative charge
     • Is carried by electrons. If there are more negative than positive charges, then the object is negatively charged.
       • • 6 positive charges 9 negative charges: 6 + (-9) = -3
           • The net charge is -3. This means that the object is negatively charged.
       • Electrons are added/gained giving the object an excess of electrons.
   • Even though there are only two types of charge an object can be neutral meaning it does not have an excess of neg or pos charges. number of neg charges = number of pos charges
     • • 6 positive charges 6 negative charges 6 + (-6) = 0
         • The net charge is 0. this means that the object is neutral . positive charges = negative charges.

3. Tribo-electric charging.

   • Objects can become charged in many ways, including friction. In this way they can lose or gain negative charges.
     • How it works: When two neutral substances are rubbed together, eg: wool cloth and a steel bar, friction causes the transfer of electrons to occur. The steel bar will become neagtively charged and the woolen cloth will become positively charged. This is because according to the Tribo Electrical Series table, wool has a tendency to become positively charged and because steel is neutral it can become either negatively charged or positively charged. In this case negatively charged.
     • Electrification is the addition or removal of electrons from an object.
   • Tribo Electrical series: strong positive: h-l Dry human skin Perspex Glass Nylon Wool Neutral: Cotton Steel Wood Strong negative: Rubber balloon Copper Foam plastic Silicon Teflon

4. Forces between charges:

   • Electrostatic forces between like charges is repulsive.
   • Electrostatic forces between opposite forces is attractive.
   • The closer together the charges are, the stronger the electrostatic force between them is.

5. Conservation of charge.

   • The total net charge of an isolated system remains constant (the same) suring any physical process (electron transfer).
   • Charge on each of two identical size conductors
     • When two identical objects ( same size, material and shape) are brought into contact with one another,they have the same size net charge and when separated from each other they will both either be negatively or positively charged. like charges repel.
       • Two objects with charges Q and Q .
         • Are allowed to make contact.
           • Are separated from each other.
     • This equation is only for identical size conductors Q = Q + Q