Measuring Charge

Electrons determines charge and amount of charge.

Charge is a measure of an electron.

Unit of charge = Coulomb (C)

Charge on a single electron = -1.6 x 10^-19 C

Any charged object will be attracted to a neutral object

Force of repulsion - occurs with only like charges (1 way)

Force of attraction - occurs with opposite charge or neutral charge

When do charges attract or repel?

Which transfers: electrons or protons? Why?

Polarization of a neutral object

Electric Force

Two factors that affect the exerted force of charged objects

• Distance (inverse power relationship)

• Charge (direct relationship)

Electric Force can be

• Charged w/ same type of charge

• Charged with opposite charges

Coulomb’s Law

Equation: F= [(k)(Q1)(Q2)]/(d)^2

F = magnitude force experienced

k = Coulomb’s constant (9.00x10^9 Nm^2/C^2)

Q = charged objects

d = distance between centers of objects

The direction of force depends on the charges involved.

Newton’s law of universal gravitation

F (grav) = [(G)(m1)(m2)]/(d)^2

F = magnitude force experienced

m = masses of objects

g is used to calculator for objects near earth’s surface

Types of Objects in Electrostatics

Conductors

• Materials that allow electrons to transfer across the entire exterior surface of an object

• electrons travel due to chemical structure

• electrons want to evenly spread out

• ex: metals, water, carbon

Insulators

• Materials that do not allow electrons to transfer across the surface of an object

• the charge will remain at the location of charging

• material of insulators prevents electrons from evenly distributing

• ex: wood, dry air, glass, rubber

Semi-Conductor

• ex: Si and Ge

Separation of Charge (Polarization)

• process of separating opposite charges within an object

  • object’s charge overall stays neutral, but charges rearrange within

  • charges never change (electrons never transfer)

Grounding

• “uncharging”

• removing excess charge by process of transfer of electrons between charged object and another larger object

• needs conductive pathway

Charging by Friction

• Rubbing an object

  • as they are in close contact, it’s as if they are sharing electrons

  • from least electron-affinity object to most electron-affinity object

• In result, two objects will have equal and opposite charges

Charging by Conduction

• charge neutral object by contact of charged object

• in result, both will have same type of charge (not magnitude)

Charging by Induction

• charge an object without touching with charged object

  • polarize first, then ground, and remove inducing object

• distract wanted charge, ground the removed charge, left with wanted charge

• in result, two objects will have opposite charge