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Electricity

charge

  • quantity of charge on 6,25 × 10^18 electrons

  • may be pos or neg. Pos caused by deficit, neg caused by excess

Electricity Symbols

Emf

→ E

  • amount of charge that can be supplied per coulomb of charge

Series

  • ET = E1 + E2 + E3

  • produces stronger current - total EMF increases

Parralel

  • Et = E1 = E2 = E3

  • positive and negative connected seperately

  • less resistance, less internal enerngy lost, last longer

Potenial difference

  • V (potential difference) = W (work done) / Q (charge)

Current

  • convential flow → positive to negative

  • current in metal is conducted by negative electrons → negative to positive

    • based on direction positive charge would take → positive to negative

  • I (current strength) = Q (charge) / t (time)

Conduction in a metal

  • in metals atoms are packed close in crystal lattice

  • outermost electrons can escape to form positive metal ions → free electrons

  • negative charged electrons are attracted to positive terminal while metal ions remain because crystal lattice

  • movement effected by collision with positive metallic ions causing resistance

    → every electron that leaves a conductor at positive terminal is replaced at the negative terminal

    • overall charge therefore 0

Resistance

  • caused by collisions between electrons and metal atoms that interefere with the flow of charge

    Things that effect it

    1) type of metal

    2) length of the conductor

    3) thickness (cross sectional area) → thicker = less

    4) temperature

  • R (resistance) = V (voltage) / I (current strength)

Ohms law

  • for a given resistor (which is normally the same in the circuit) → V directly proportional to I

  • V (voltage) = I (current strength) x R (resistance)

Resistors in series

  • resistors in series divide PD (voltage)

  • V = V1 + V2 + V3 …

Resistors in parralel

  • current dividers

  • i know the formula for this already

  • more current flows through the resistor with less resistance

Meters

  • ammeter → strength of an electric current (A - amperes) → low resistance and connected in series

  • voltmeter measures voltage (pd between two points in a circuit) → high resistance, connected in parralel

Power

  • P (watts - W) = W (work - J) / t (time)

Definitions

potential difference → the potential difference between two points in a circuit is the energy required to move one coulomb of charge between the points

current → an electric current is the flow of charge (positive to negative) from one point to another in an electrical circuit

current strength → the rate at which charge passes a given point in a conductor

resistance → the ratio of potential difference across the ends of a conductor and current strength

ohms law → current strength is directly proportional to the potential difference between the ends of a given resistor provided that temperature remains constant

power → the rate at which work is done

coulomb → the quantity of charge that passes through a conductor when a current of one ampere flow for one second