Electric Charges and Electric Field Quick notes
1. Electric forces between atoms and molecules hold them together to form
liquids and solids
2. Many forces (elastic, normal and friction) are considered to occur due to
electric forces
3. Elektron means amber. If an object is rubbed it attracts pieces of dust. We
now call this static electricity.
4. If an object becomes changed while rubbing it with a cloth, it possesses a net
electric charge.
5. Two types of electric charge are positive and negative
6. Charged particles repel like charge particles and attract the opposite charge
7. Law of Conservation of energy: the net amount of electrical charge produced
in any process is zero.
8. Protons are positive, electrons are negative and neutrons are neutral
particles.
9. Ions are atoms that lose or gain electrons
10. Polar atoms are neutral atoms but charge is not uniformally distributed
11. Conductors of electricity are materials such as iron that transfer electricity
from a charged material to an uncharged material. Conductors have free
electrons, that readily move toward a charged object
12. Insulators are materials such as rubber that do not transfer electricity. They
have tightly bond electrons
13. Semiconductors are in between the two
14. Charging by conduction is the charging of an object through touch, changing
the net charge of that object
15. Charging by induction is when charges are separated in an object due to the
proximity of another charged object, but the net charge does not change
16. An object which is grounded has its conducting wires connected to the
ground and the ground accepts or gives up electrons easily acting as a
reservoir for the electrons.
17. An electrosocope is a device used for detecting charge. Gold leaves move
apart if the object brought up to the device is charged.
Coulomb’s Law
1. Charles Coulomb (1736-1836) investigated electric forces in the 1780’s
2. Concluded that the electric force on one charged object on another charged
object is directly proportional to the charge on each of them
3. Led to Coulomb’s Law which is: F = k (Q1Q2/r2 ) where k is a proportionality
constant, the force is the magnitude of one charged object on another, Q is
the magnitude of each object and r is the distance between them.
4. The direction of the electric force is always along the line joining the two
charges and depends on if they have the same sign or different signs
5. The SI unit charge is the Coulomb
6. k = 8.988 x 109 N m2/C2
7. Coulomb is very large and is the amount of charge is you placed on two
objects, one cm apart, each object would exert a force of 9x109
8. Objects with static electricity are in the microcoulomb
9. The elementary charge is the smallest charge found in nature and is:
e=1.6022 x 10-19C
10. Electrons aare quantized (existing in discrete amounts)
11. Coulomb’s Law looks very much like the law of universal gravity
12. When determining r, if the tow objects are spherical we use the distance
between their centers
13. Coulomb’s law only works with charges at rest and only gives the
electrostatic force.
14. When uses Coulomb’s Law we ignore charges and use magnitudes only.
15. The electrostatic force is a vector, with magnitude and direction
16. It is important to draw a free body diagram in applying Coulomb’s Law
17. Add all forces together to obtain the net force of an object