Electrical Physics

• Net Charge: when the number of pos and neg charges of an object are unbalanced
• MEASURING CHARGE

  Elementary charge

  +e = proton -e =electron
• Coulomb (C): 1 coulomb is equivalent to the combined charge of 6.2 x 10^18 protons

  Variable of "q"

  • charge of one proton = +1.6 x 10^-19 C
  • charge of one electron = -1.6 x 10^-19 C
• Metals - Conductors

  • outermost electrons are only slightly attracted to their nuclei
  • loosely held electrons can jump from one atom to another, moving freely
• Non-Metals - Insulators

  • outer electrons are tightly bound to their nucleus and cannot readily move
• Energy and Potential Difference

  • Chem E is stored in a battery until a redox reaction occurs, transforming Chem E to Elec Pot E
  • Pot E is stored in the electric field formed by charge build up in battery's terminals
  • When battery is isolated the charge build up opposes the redox, redox reaction stops, allowing battery to contain components for years
  • Once battery is reconnected, redox continues, maintaining the charge difference between terminals
• Potential Difference/Voltage: the difference in electrical potential energy between battery terminals

  Measured in Volts (V)

  Formal definition: the amount of elec pot E given to each coulomb of charge
• $V=$$E/q$

  V: pot. diff. (V)(JC^-1)

  E: elec. pot. E (J)

  q: charge (C)
• Voltmeter

  -> measures potential difference

  -> must be added in parallel
• Electric circuit: a path made of conductive material, through which charges can flow in a closed loop

  Electric Current: the flow of charges

  Electric Flow: the movement of electrons within a wire
• Convectional Current -> flows from pos to neg terminal

  vs

  Electron flow/current -> the flow of electrons from neg terminal to pos power supply

  • amount of charge is equal in both
• Current (I): the amount of charge that passes through a point per sec

  Measured in amperes

  1 amp = 1 Cs^-1
• $I=$$q/t$

  I: Current (A)

  q: charge (C)

  t: time (sec) elapsed

  $q=$$qe *$$ne$

  qe: charge of one elec (-1.6 x 10^-19 C)

  ne: number of electron flow
• Ammeter

  -> measures current

  -> must be added in series

  • current remains constant throughout
• Work Done by circuit

  $E=$$△VIt$
• Power: the rate of doing work

  A measure of how fast energy is converted
• Resistance (R): measure of how hard it is for a current to flow through a particular material

  Measured in Ohm's (Ω)

  • conductors have low resistance
  • insulators have high resistance
• Ohm's Law

  : current is directly proportional to potential difference

  $ΔV=$$IR$
• Ohmic Conductors (resistors)

  -> obey Ohm's Law

  Show a linear relationship between voltage and current
• Non-ohmic Conductors

  -> show non linear relationship

  Dont obey Ohm's Law/
• Series Circuits

  when one component breaks/removed, circuit is incomplete -> isn't used in housing

  • current is constant throughout
• Kirchoff's Loop Rule ->the sum of pot diff across all elements of a circuit equal zero

  (a version of the law of conservation)
• Electromotive Force (EMF): the work done on the charges to provide a potential diff
• Resistance in Series is addition
• Resistors in Parallel

  • current will flow through path of least resistance
  • pot diff is the same across each branch
  • current is addition
  • Kirchoff's Junction Rule ->current flowing into the junction must equal current flowing out
  • the addition of a resistor in parallel allows more current as a new pathway is added -> total resistance decreases
  • total resistance is the addition of inverses
  • R total is less than R of the smallest resistor