Topic 6 - Field and Forces
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[edit] Forces and Fields
[edit] Fields
Fields are defined as Forces that Act at a distance. There are four known fields - Gravitational, Electro-Magnetic, Weak Nuclear Force and Strong Nuclear Force - Weakest to strongest.
In general, a the strength of a field is proportional to both the attraction of the object emitting the field, and the attraction of the object in the field. Take the earth, for example. The gravitation force exerted by the earth on an object is proportional to the mass of the earth and the mass of the object. The force is also inversly proportional to the distance between the objects squared.
[edit] 6.2 Electric Force and Field
[edit] Electric Charges
There are two types of electric charges: positive and negative. If a substance has an excess of electrons then it has a negative charge. On the contrary, if a substance has a deficiency of electrons then it’s positively charge.
[edit] Charge
Charge is measured in units called Coulombs, C, and is given the symbol q. 1 C = the charge on 6.25 x 1018 electrons
The charge on one electron = -1.602 x 10-19 C The charge on one proton = +1.602 x 10-19 C
[edit] Law of Conservation of Electric Charge
The Law of Conservation of Electrical Charge says that the total amount of electrical charge in a closed system is constant - no charge is lost in an electrical system.
[edit] Conductors, Semiconductors And Insulators
Conductors are materials which allow electrons to pass through them easily. Most metals are conductors, although copper and aluminium are the most effective conductors. Aqueous ionic compounds are also conductors, as is graphite.
Insulators are materials which do not allow electrons to flow through them easily, such as glass, most plastics and other organic compounds.
Semiconductors are materials which demonstrate properties typical of both conductors and insulators. They are not as effective as conductors, but still allow some electrons to flow. A common semiconductor is Silicon.
[edit] Coulomb’s Law
On the basis of his experiments, Coulomb deduced that each point charge in a system would be the target of an equal amount of force. The force is proportional to the charges of each point charge, and inversely proportional to the distance between the charges squared.
F = ( K )( q1 * q2 ) / ( r^2 )
Where F is the induced force, q1 and q2 are the charges of the point charges, r is the distance between the point charges and K is the Coulomb Constant; K = 8.987 x 10^9[1].
1:[1]
