electrostatics – the study of electrical charges that can be collected and held in one place. also...

Electrostatics – the study of electrical charges that can be collected and held in one place.

Also referred to as Static Electricity

Electric Charge ( q ) – the quantity of unbalanced electricity in a body (scalar) two different charges exist: “positive”

and “negative” Units – Coulombs (C)

+

-

Neutral

contains all electrons

Positive Ion

loses 1 or more electrons

Negative Ion

gains 1 or more electrons

1. The total charge in any closed system never changes. (The combined total charge of two objects remains the same.)

2. Individual charges can neither be created nor destroyed; they can only be transferred from one object to another.

Insulators – material through which charges will not move easily.

Ex – glass, dry wood, rubber, most plastics, cloth, distilled water, and dry air.

Conductors – materials that allow charges to move about easily.

Ex – metals, water solution

Can air become a conductor?

The electric fields in storm clouds transforms the surrounding air into a conductive plasma. This plasma easily conducts lightning.

Grounding - removing excess charge from a charged body by connecting it to the Earth.

Leakage - the discharging of a charged object due to the acceptance of electrons by the air.

Elementary Unit of Charge ( e ) – the amount of negative charge that is possessed by the electron and the amount of positive charge possessed by the proton.

1e = 1.60 x 10-19 C

All electrons have one specific charge. Objects become charged by gaining or losing whole

electrons. Must be a multiple of 1.60 x 10-19 C

Oil droplet Excess electron

Polarization – to cause one side of an object to become negative, and the other side to be positive. The overall charge of the object is

neutral.

Conduction – charging a neutral object by touching it with a charged object.

totalqq =

# of objects

* Not on Reference Table

Induction – causing a neutral object to become charged without direct contact between the charged object and the neutral object.

The charged object only served to polarize the object being charged.

They do not come into contact with each other. No electrons are transferred between them.

The object being charged is touched by a ground; electrons are transferred between the ground and the object being charged

The object being charged ultimately receives the opposite charge than the charged object used to polarize it.

Electrostatic Force (Fe) – the field force exerted between any objects bearing charge (vector)

Point Charge – a charged conducting sphere that interacts with other charged objects in a manner as though its charge were located in its center.

Charge concentratedat center of sphere.

= 8.99 x 109 N•m2/C2

1 2e 2

kq qF =

r

Charles Augustine de Coulomb

How can a force be exerted across what seems to be empty space?

All charged objects create an electric field which extends outward into the space surrounding it.

Electric Field Strength ( E ) – a vector quantity that relates the force exerted on a test charge to the size of the test charge

Test charge – a small positive charge that is placed near another charge in order to observe an electrical field.

The test charge feels a force (red arrow).

Units - N/C (Newton / Coulomb)

eFE=q

1. The strength of the E-field is indicated by the spacing between the lines. The field is stronger where lines are close together.

2. The E-field is always directed perpendicular and touching the surface of the object.

3. Field lines always leave a positive charge and enter a negative charge.

4. The direction of the arrow represents the field direction.

5. Electric field lines should NEVER cross.

+

-

+

+

-

+

-+

++

--

+-

- -

How could you increase the gravitational potential energy of a ball on Earth?

Electrical Potential Energy ( W ) – potential energy associated with an object due to its position relative to a source of electric force (scalar)

Units – Joules (J)

In which scenario does the test charge have

the greatest potential energy?

In which scenario does the test charge have

the greatest potential energy?

Potential Difference ( V ) – difference in electric potential energy between two points (scalar)

Units – Volts (V)

WV=

q

Electronvolt – the energy that an electron (or proton) gains when accelerated through a potential difference of 1 Volt.

A unit of energy commonly used in atomic and nuclear physics because of its convenient small size.

1 eV = 1.60 x 10-19 J