electricity

Cards (44)

  • the current in an electric circuit flows from negative terminal to the positive
  • What is current? current is the rate of flow of charge around a circuit
  • how can we measure current
    Using an ammeter
  • what is current measured in
    Amps
  • formula for charge flow: Charge flow = current x time

    Q=It
  • what is resistance: the measure of how difficult it is for the charge to travel around a circuit or through a component in the circuit
  • relationship between current and resistance
    inversely proportional
  • What is resistance measured in?
    Ohms (Ω)
  • what is a resistor: component designed to provide a certain amount of resistance
  • what is a variable resistor: allows you to change the amount of resistance in the circuit by moving a slider
  • What is potential difference measured in? the amount of energy per unit of charge flowing in the circuit
  • what is the PD of a component measured by: voltmeter
  • How is a voltmeter connected in a circuit? it is connected in parallel to the component
  • Formula for potential difference
    V = IR
  • series circuit rules: current flowing through each component is the same

    total PD of cell is shared between each component

    in a series circuit, total resistance is the sum of all resistance in all components
  • parallel circuit rules: current flowing through each circuit is shared

    total pd is the same between components

    adding more resistors in parallel decreases the total resistance-> this is because the total PD is the same across each resistor

    if one pathway is broken the other still works
  • Formula for energy transferred: Energy transferred = power x time

    E = Pt

    Energy transferred = charge flow x pd

    E = Qv
  • what are parallel circuits: circuits with more than 1 loop
  • what is DC: direct current - charge flows in one direction
  • What is AC? alternating current - charge can flow back and then forwards
  • what is the voltage & frequency of mains: 230V & 50Hz
  • formula for frequency
    frequency = 1 / time period
  • how do you get a large amount of power? by either having a large PD or large current
  • what is the problem with having a large current to transport large amounts of power: the wires get hot and lots of energy is transferred as heat to the surrounding
  • why do we use a large PD when transporting a large amount of power: this means that there is a very low current which delivers high power but loses much less energy as heat - this means it is more efficient
  • role of power station: generates electricity

    need to meet the demand across the country
  • step up transformer: increases the PD to around 400000 V

    reduces the current

    power is transmitted efficiently
  • high-voltage transmission lines: above or below ground

    high voltage

    low current

    well insulated
  • step down transformer: decreases the PD to 230V

    increases current

    power supply is safe for consumers and appliances
  • formula for power: power = current x pd

    power = current ^2 x resistance
  • formula for efficiency: efficiency = useful output work/total input work x 100%
    • Connect circuit as per diagram
    • Clip crocodile clips on resistance wire, 100cm apart
    • Record readings of ammeter and voltmeter
    • Move one clip to make the distance 90cm, record readings again
    • Repeat previous step, reducing length by 10cm each time until minimum length of 10cm is reached
    • Calculate resistance for each length of wire using R=V/I
    • Plot a graph of resistance vs. length of wire
    • Use results to analyze the relationship between resistance and wire length.
  • static electricity is due to the build up of electric charge
  • it is called 'static' electricity because electricity is unable to flow
  • the build up of electric charge can cause dangerous sparks
  • lightning is an electrical discharge that occurs when charge builds up in the clouds
  • static electricity is due to an electric charge that builds up on an insulator
  • an insulator is a material that does not conduct electricity
  • friction can be used to create a static charge
  • If an insulator is rubbed with a cloth, it can become charged in two ways:

    electrons move from the cloth to the insulator

    or

    electrons move from the insulator to the cloth