U2: Electric Charge and Electric Field

Atomic and molecular interactions are known to be manifestations of the electromagnetic force.

● It includes moving electricity and magnetism.

Some of the most basic characteristics of static electricity:

● The effects of static electricity are explained by a physical quantity not previously introduced, called electric charge.

● There are only two types of charge, one positive and the other negative

● Like charges repel, whereas unlike charges attract

An atom includes negative electrons orbiting its positive nucleus

● The nucleus is positive due to the presence of positively charged protons

○ The charges of protons and electrons are identical in magnitude but opposite in sign

Charges in atoms and molecules can be separated

● Ex: rubbing, batteries, chemical interactions

● Some atoms and molecules have a greater affinity for electrons than others

● The law of conservation of charge states that total charge is constant in any process

● No charge is actually created or destroyed when charges are separated

Coulomb’s law calculates the magnitude of the force between two point charges separated by a distance

● 𝐹 = 𝑘(|𝑞1𝑞2|)/𝑟2

● It is the mathematical formula for electrostatic force - the amount and direction of attraction or repulsion between two charged bodies

A field is a way of conceptualizing and mapping the force that surrounds any object and acts on another object at a distance without apparent physical connection

● It includes a point charge (a particle having a charge) that acts on a test charge at a distance

● 𝐸 = 𝐹/𝑞

○ E is the ratio of the Coulomb force to the test change

○ F is the electrostatic force

■ E is in the same direction of F

These are steps you can take to solve electrostatics problems:

● Examine the situation to determine if static electricity is involved

○ This may concern separated stationary charges, the forces among them, and the electric fields they create

● Identify the system of interest

○ This includes noting the number, locations, and types of charges involved

● Identify exactly what needs to be determined in the problem

○ Determine whether the Coulomb force is to be considered directly

○ It may be useful to draw a free-body diagram

● Make a list of what is given or can be inferred from the problem as stated

○ Identify the knowns

● Solve the appropriate equation for the quantity to be determined

● Examine the answer to see if it is reasonable