Physics 2 Prelim (Electrostatics + Electric Fields)

• Static Electricity occurs when an object obtains a net amount of positive or negative electric charge, creating an imbalance that wants to be returned to equilibrium
• Like charges repel from one another
• Opposite charges attract one another
• Atoms contain charged particles, positive protons and negative electrons
• There's an equal number of protons and electrons making the electric charge of sn atom equal to 0
• In solid materials protons stay fixed, but some electrons are free to move around
• Free electrons reside in an atom's outer shell as valence electrons are easily plucked off and carried sround when acted upon an 'outside force'
• Materials that are conductors let free electrons move freely throughout the solid
• Insulators hold on to electrons tightly, limiting their flow
• Negative charge = too many electrons
• Positive charge = missing free electrons
• When you rub a glass rod (electrically neutral) with q cloth, the rod will have an overall positive charge (friction)
• No new charges are created during friction, it's still 0
• Law of Conservation of Electric Charge - You can never create a net electric charge, it can only move from one place to another
• Charging by contact - dome electrons will jump from the neutral to the positive until they both have the same distribution
• Materials don't have to touch in order for their electrons to get all rearranged
• Polarization occurs when you bring two objects together and one object redistributes its charge because of the other object
• Charging by Induction - Creating a net charge without contacting another object
• The Earth's surface is a fairly good condictor for most places, it can be considered neutral
• Connecting a charged object to the ground creates a way for the charge to leak into the Earth, rendering the object electrically neutral
• Grounding - sticking something onto the earth's surface/ground to make the object positively charged (making the negative charges into the earth's surface)
• Charge is denoted by the symbol "q"
• Charge units are called Coulombs denoted by symbol "C"
• There are 6.24 x 10^18 electrons for every negative Coulomb
• Elementary Charge, denoted by symbol "e" has a value of 6.24 x 10^18
• Protons have a charge of positive e and electrons have a charge of negative e
• Coulomb's Law states that F = k(q1q2/r²) where in (F is force) (k is Coulomb's constant) (q1q2 is the product of two charges) (r² is the distance between them squared)
• As the distance is squared, when the distance between object doubles, the force between them reduces to a quarter of the original value
• Most of the time the constant is

  k = 9 x 10^9 Nm²/C²
• Electrostatic forces can either be attractive or repulsive, depending on the signs of the charges
• What is the electric force of this?

  Given:

  q1 = -1.6x10^-19 C

  q2 = -1.6x10^-19 C

  r = 1 x 10^-9 m

  k = 9 x 10^9

  Use Coulomb's Law in Solving

  2.3 x 10^-10 N
• Electric forces are used to bring power to your home, charge your computer, and light up the screen that you're using to watch a video
• Michael Faraday hypothesized that every charged object generates an electric field that permeates space and exerts a force on all charged particles it encounters
• An electric field is a measurable effect generated by any charged object
• A field carries energy and passes it on to other charged materials by exerting electric forces
• Positive point charge is denoted by symbol "Q"
• Small positive test charge is denoted by "q"
• Electric field = force/magnitude of test charge

  E = F/q
• Electric field equation

  E = k(Q/r²)
• Electric field lines are called vectors that have a purpose to show the magnitude and direction of force exerted on any nearby positive test charge