Chapter 8

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Cards (16)

  • Define electrical current
    The rate of flow of charge
  • Electrical current is defined as the rate of flow of charge and measured in amperes (A)

    I=I =ΔQΔt \frac{\Delta Q}{\Delta t}
  • electrical charge is measured in Coulombs which are defined as the electrical charge flowing past a point in one second when there is a current of one ampere.
  • The elementary charge is equal to 1.6×10−191.6 \times 10 ^ {-19}
  • The charge on an object is the result of the loss or gain of electrons therefore the net charge on an object is given by:
    where n is the number of electrons added or removed and e is the elementary charge
    Q=Q =ne ne
  • The oil drop of experiment showed that the charge on the droplets was quantised, meaning that the charge on the droplets was quantised so it could only take values which were multiples of the elementary charge
  • In metals, current is the flow of electrons. Most of the electrons remain fixed to their atom however some of them are free to move (delocalised electrons). To make these electrons move through the wire to create current, one end is made positive and the other negative so that the electrons are attracted to the positive end and therefore flow through the wire
  • To increase the current in a wire, the number of electrons can be increased by increasing the cross-sectional area of the wire or the electrons can be made to move faster through the wire
  • In electrolytes, electrical current is the flow of ions. The positive cations move towards the negatively charged cathode an the negative anions move to the positively charged anode creating a movement of charge carriers
  • An ammeter is used to measure current and is placed in series to reduce their effect on current
  • Kirchhoff's first law states that for any point in an electrical circuit, the sum of currents into a point is equal to the sum of currents out of that point.
  • Number density is the number of free charge carriers per unit volume.
  • The higher the number density of a material the more conductive it is. Insulators have a low number density while conductors have a high number density and semiconductors are in between these.
  • Free electrons move through a wire randomly, they repeatedly collide with the positive ions in the metal as they drift through the wire.
  • The equation for current is also

    I=I=AnevA n e v
  • If the cross sectional area of a wire decrease, the drift velocity must also increase in order for the current to be the same.