1. Electrostatics
ConcepTests

2. In The Beginning
Amber: Greeks noticed that when rubbed, attracts small things (amber stuff, or electricity).
Rubbed Items Attract New Force
Force Agent  Electromagnetic Charge

3. Electromagnetism Electromagnetism Electrostatics Electrical Currents
Electromagnetism (Currents & Magnetic Fields)

4. Types of Charge
French Botanist C. Dufay found 2 different types of charge
Franklin arbitrarily called charges + & -
+ & - Charges Can Add to Zero

5. Charge is Quantized Charge is Conserved Charge Is What It Does
Charges
Charge is Quantized
qe= -1.6x10-19
Charge is Conserved
Charge Is What It Does

6. Conductors
Conductors: electric charges move freely due to an electric force (or field)
Ex: Copper, aluminum and silver
Charge a Conductor: the charge distributes itself over the entire surface of the material

7. Insulators Insulators: e charges do not move freely
Ex: Glass and rubber
Charge insulators by rubbing: only the rubbed area becomes charged

8. Charging by Conduction
Charged rod contacts the sphere
Some electrons on the rod can move to the sphere
When the rod is removed, the sphere is left with a charge
The object being charged is always left with a charge having the same sign as the object doing the charging

9. Charging by Induction
When an object is connected to a conducting wire or pipe buried in the earth, it is said to be grounded
A negatively charged rubber rod is brought near an uncharged sphere

10. Charging by Induction, 2 The charges in the sphere are redistributed
Some of the electrons in the sphere are repelled from the electrons in the rod

11. Charging by Induction, 3
The region of the sphere nearest the negatively charged rod has an excess of positive charge because of the migration of electrons away from this location
A grounded conducting wire is connected to the sphere
Allows some of the electrons to move from the sphere to the ground

12. Charging by Induction, final
The wire to ground is removed, the sphere is left with an excess of induced positive charge
The positive charge on the sphere is evenly distributed due to the repulsion between the positive charges
Charging by induction requires no contact with the object inducing the charge

13. A positively charged object is placed close to a conducting object attached to an insulating glass pedestal (a). After the opposite side of the conductor is grounded for a short time interval (b), the conductor becomes negatively charged (c). Based on this information, we can conclude that within the conductor
both positive and negative charges move freely.
only negative charges move freely.
only positive charges move freely.
We can't really conclude anything about the sign of the charges that move.
ANSWER: D. The same result is achieved regardless of whether the charge carriers are positive or negative. So, it could be either that positive charges left or additional negative charges entered the conductor.

14. Three pithballs are suspended from thin threads
Three pithballs are suspended from thin threads. Various objects are then rubbed against other objects (rubber against fur, glass against silk, a plastic comb against hair, etc.) and each of the pithballs may have been charged by touching it with one of these objects. It is found that pithballs 1 and 2 repel each other and that pithballs 2 and 3 repel each other. From this we can conclude that
1 and 3 carry charges of opposite sign.
1 and 3 carry charges of equal sign.
all three carry the charges of the same sign.
one of the objects carries no charge.
we need to do more experiments to determine the sign of the charges.
Charges of equal sign repel, so 1 and 2 carry charges of equal sign and so, too, do 2 and 3.

15. Three pithballs are suspended from thin threads
Three pithballs are suspended from thin threads. Various objects are then rubbed against other objects (ribber against fur, glass against silk, etc.) and each of the pithballs may have been charged by touching it with one of these objects. It is found that pithballs 1 and 2 attract each other and that pithballs 2 and 3 repel each other. From this we can conclude that
1 and 3 carry charges of opposite sign.
1 and 3 carry charges of equal sign.
all three carry the charges of the same sign.
one of the objects carries no charge.
we need to do more experiments to determine the sign of the charges.
Answer: 5. Charges of opposite sign attract, charges of equal sign repel, and any type of charge attracts a neutral object. So 1 and 2 either carry charges of opposite sign or one of the two is neutral and the other charged. Since 2 and 3 repel, however, we know that 2 and 3 carry charges of equal sign. So there are two possibilities: 2 and 3 carry charges of equal sign and (i) 1 is neutral, or (ii) 1 carries a charge of the opposite sign to that of 2 and 3.

16. Two uniformly charged spheres are firmly fastened to and electrically insulated from frictionless pucks on an air table. The charge on sphere 2 is three times the charge on sphere 1. Which force diagram correctly shows the magnitude and direction of the electrostatic forces:
Answer: 5. The magnitude of the electrostatic force exerted by 2 on 1 is equal to the magnitude of the electrostatic force exerted by 1 on 2. If the charges are of the same sign, the forces are repulsive; if the charges are of opposite sign, the forces are attractive.

17. Consider the four field patterns shown
Consider the four field patterns shown. Assuming there are no charges in the regions shown, which of the patterns represent(s) a possible electrostatic field:
(a)
(b)
(b) and (d)
(a) and (c)
(b) and (c)
some other combination
None of the above.
Answer B. Pattern (a) can be eliminated because field lines cannot simultaneously emanate from and converge at a single point; (c) can be eliminated because there are no charges in the region, and so there are no sources of field lines; (d) can be eliminated because electrostatic field lines do not close on themselves.

18. Charles Coulomb 1736 – 1806 Studied electrostatics and magnetism
Investigated strengths of materials
Identified forces acting on beams

19. Vector Nature of Electric Forces
Two point charges are separated by a distance r
Like charges produce a repulsive force
The force on q1 = - q2
This is a N3L deal

20. Electrical Forces are Field Forces
This is the second example of a field force
Gravity was the first
For field forces, the force is exerted by one object on another object without physical contact
similarities and differences between electrical and gravitational forces
Similarities: Differences:
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21. The Superposition Principle
Fnet (resultant force) on any one charge equals the vector sum of the forces exerted by the other individual charges that are present.
Huh?