FRICTION AND CHARGE

Welcome to Free WAEC and JAMB expo, read on and see whats going to come out: 


Some objects such as glass rods or an ebonite rod acquire the property of being able to attract small pieces of paper after they have been rubbed with another material such as silk or fur. This
phenomenon belongs to the branch of physics called electrostatics or static electricity. It involves the study of static electric charges. Before rubbing, these rods do not attract the small pieces of paper. This implies that the friction due to rubbing has changes the nature of the surfaces of the rods. We say that friction has caused the rods to become electrified or charged. Here are some things one must know about friction. This free topic must be understood before WAEC and JAMB.
It produces different kinds of charges on different materials.
Like charges always repel each other while unlike charges attract.
Only two kinds of charges exist.

Atomic explanation of charging by friction:

1. Matter consists only of indivisible particles called atoms. Each atom has negatively charged electrons orbiting around a small dense nucleus. The nucleus consists of positively charged particles called protons and the neutral particles called neutrons.
 
2. In its normal state, an atom has equal number of electrons and protons, thus it is electrically balanced or neutral.
 
3. The electrified state is a state in which the electrical balance is disturbed. This occurs when some electrons are removed from the atom or added to it. The atom is now said by ionized.
 
4. If an atom has some of its electrons removed, it becomes positively charged. If electrons are added to the atom, the atom becomes negatively charged.
 
5. In charging by friction (such as rubbing glass rod with silk) some electrons from the surface atoms of one object (the glass rod in this case) are transferred to the other object (the silk cloth) the glass rod becomes positively charged as it now has few fewer electrons than protons. The silk becomes negatively charged as itt has gained excess electrons.

Charge can neither be created or destroyed it can only be simply transferred from one material to another.

Production of charges
There are three ways a charge can be produced as follows; 

By friction;
Earlier we learnt that the addition or removal of electrons from a material by friction such as rubbing causes the material to become charged negatively or positively. Typically, insulators are charged by friction as the charges tend to stay localized and the excess electrons do not move easily between the materials.
   
By contact;
When a negatively charged material (an ebonite rod charge by rubbing with silk) comes into contact with an uncharged conductor (metal sphere) the rod transfers some of its excess electrons to the metal sphere while the metal sphere becomes negatively charged too. Similarly when a positively charged material (glass rod rubbed with silk) comes into contact with an uncharged metal sphere, electrons from the metal sphere will be attracted towards the positively charged rod. This will leave the metal sphere with fewer electrons positively charged. After charging by contact, the object has fewer charges than it started out with.

By induction;
Induction is the process of charging a conductor without any contact with the charging body.

Measurement of charge:
Electric charge (both positive and negative) is measured in coulombs C. This is the SI unit of electric charge, it can be defined from the equation relating electric charge Q, electric current I and time t.
                                        Where Q=It
One coulomb (1C) is the quantity of electric charge that passes through a given section in a circuit when a steady current of one ampere flows for one second. The charge of one electron is -1.6x10e-19 C while that of a proton is 1.6x10e-19 C. The number of electrons or protons in 1C = Q/e =6.25x10e18

In other words one Coulomb consist of 6.25x10e8 electrons or protons. This shows that the coulomb is a very large quantity. Thus for most practical purposes, we use sub multiples of the coulomb. The most common sub multiples used are milli coulombs (1mC = 10e-3) and micro coulombs (1uC = 10e-6C)


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