Electrostatics

• Static electricity occurs when an object obtains a net amount of positive or negative electric charge, creating an imbalance that wants to be retuned to equilibrium.
• An atom contains

  1. Protons
  2. Neutrons
  3. Electrons
• The net electric charge of an atom is 0 (electrically neutral).
• 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, and are easily plucked off and carried around when acted upon by an 'outside force'.
• How easy an electron to move around depends on the material.

  • Conductors: Let free electrons move freely throughout the solid (e.g., copper)
  • Insulators: Hold on to free electrons tightly, limiting their flow (e.g., wood)
• Imbalance of electrical charge causes these charged particles (free electrons) to move in the first place.
• Imbalance of electrical charge occurs when some part of an object has a different number of free electrons than another part.
• • Negative charge = Too many electrons
  • Positive charge = Missing (free) electrons
• Charging by friction occurs when an object is rubbed against another object.
• Law of Conversation of Electric Charge states that you can never create a net electric charge. Instead, charge can only move from one place to another.
• When two objects touch, charges move between them (Charging by contact).
• Materials don't actually have to touch in order for their electrons to get all rearranged.
• Polarization is the process wherein we redistribute the charge in order to create an imbalance of charge within an object that is still electrically neutral.
• Charging by induction is creating a net charge without contacting another object. It can be done by splitting an object while an imbalance was present (polarization).
• If a charged object is connected to a much larger neutral conducting object, then the net charge gets redistributed so that the smaller object loses most of its net charge.
• The earth's surface is a fairly good conductor and 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. This is called grounding.
• • Opposite charges = Attract
  • Like charges = Repel
• • N (newton) = Force on charged particles
  • q (charge) = In units, called coulombs. It can have both positive and negative values.
  • e (elementary charge) = Value of the charge of a single electron in Coulombs.
  • +e = protons
  • -e = electrons
  • r = Distance between two objects
  • k = Coulomb's Law Constant
• • Charge of a single electron = 1.6x10^-19 C
  • Number of electrons in 1 negative coulomb of charge = 6.24x10^18
• Coulomb's Law states that the force between two charged particles is equal to the product of the two charges, divided by the distance between them squared.
• Coulomb's Law Formula: F = k(q1q2 / r^2) or F = k(q1q2)/r^2
• The distance (r) in the Coulomb's Law formula is squared because, just like gravitation, when the distance between objects doubles, the force between them reduces to a quarter of the original value.
• Coulomb's Law constant value (k) depends on the medium that surrounds the charges. Usually it is 9x10^9 Nm^2/C^2
• 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.
• Electric Field (is):

  • A measurable effect generated by any charged object.
  • Carries energy and passes it on to other charged materials by exerting electric forces
• • Q = Big positive point charge
  • q = Small positive point charge
• Electric Field Formula: E = F (Force) / q (magnitude of test charge) or E = k(qQ/r^2)/q -> E = k(Q/r^2)
• Electric Field Lines show the magnitude and direction of the force exerted on any nearby positive test charge.
• Electric Dipole is a pair of one positively charged particle and one negatively charged particle that are some distance apart with an equal and opposite magnitude of charge.

  
• Superposition is when the two particles that each generate their own electric field are added together to create a total electric field.

  
• 4 Important Properties of Electric Field Lines:

  • The field lines must be tangent to the direction of the field at any point.
  • The greater the line density, the greater the magnitude of the field.
  • The lines always start from positively charged objects and end on negatively charged objects.
  • The lines must never cross.
• Capacitor is an integral part of almost every electronic system partly because it can use its electronic field to store an electric charge.
• In the state of electrostatic equilibrium, the excess charges have moved as far as possible to reduce their forces on one another.
• Once the free charges are at equilibrium, their acceleration is zero, which means that there are no longer any net forces acting on them.
• Net Force=0; Electric Field=0
• Electric field inside conductors is always zero when the system is in electrostatic equilibrium.
• While the electric field inside the material is zero, an electric field exists outside the surface of the conductor.