electricty

• How does the resistance change?

  With current: As current increases, electrons (charge) have more energy. When electrons flow through a resistor, they collide with the atoms in the resistor, transferring energy to the atoms, causing them to vibrate more, making it more difficult for electrons to flow through the resistor, resulting in increased resistance and decreased current. With temperature: Similar process as atoms vibrate when hot. With length: Greater length means more resistance and lower current as electrons have to make their way through more resistor atoms. With light: LDR (Light Dependent Resistor) has lower resistance with greater light intensity. With voltage: Diodes allow current flow in one direction and have high resistance in the opposite direction
• Factors affecting resistance

  • Current
  • Temperature
  • Length
  • Light
  • Voltage
• For charge to flow

  1. Circuit must be closed (no open switches)

  2. There must be a source of potential difference (battery/cell)
• Current


  • Greater the rate of flow of charge, greater current
• Total current into a junction in Parallel Circuits = total current in each of the branches
• The gradient of each is 1/resistance, so a sharper gradient means a lower resistance
• Total Resistance in Series Circuits = R1 + R2 + ...
• In a single closed loop, the current has the same value at any point
• Q = I * t (Where Q is the charge flow in coulombs C, I is the current in amperes A, and t is the time in seconds s)
• The potential difference is the same across each "branch" in Parallel Circuits
• Resistors

  • ohmic conductor has linear graph, lamps, diodes, thermistors, and LDRs have nonlinear graphs
• Electrical Current


  The flow of electrical charge
• The greater the resistance of the component, the smaller the current for a given potential difference (pd) across the component
• Total resistance for two resistors in parallel is less than the resistance of the smallest resistor
• Parallel Circuit


  • Potential difference is the same across all branches
  • Current is shared between each of the branches
  • Total resistance is less than the branch with the smallest resistance
• Energy is transferred from chemical potential in batteries to electrical energy in wires to any form of useful energy in the devices they power
• DC

  Direct current, movement of charge in one direction only
• Mains electricity in the United Kingdom has a frequency of 50 Hz and is about 230 V
• AC

  Alternating current, comes from the mains
• Energy transferred = Charge × potential difference
• Power is the energy transferred per second, directly proportional to current and voltage
• Power loss is proportional to resistance and to the square of the current
• Parallel Circuit

  1. Components are connected separately to the power supply

  2. Current flows through each one separately

  3. You can switch each component off individually
• Series Circuit

  • Potential difference is shared across the whole circuit
  • Current is the same through all parts of the circuit
  • Total Resistance is the sum of the resistance in each component
• Series Circuit

  1. Components are connected end to end

  2. All the current flows through all the components

  3. Can only switch them all off at once
• Energy Transfers in everyday appliances

  • Kinetic energy for a motor
  • Thermal energy in a kettle
• Cabling in a plug

  • Live wire
  • Neutral wire
  • Earth wire
• Energy transferred = Power × time
• Work done is when charge flows through a circuit and is equal to energy transferred
• Ways electrical energy may be transferred by appliances

  • Kinetic energy for a motor
  • Thermal energy in a kettle
• Energy Transfers in everyday appliances
• Insulators do not conduct electricity, conductors can conduct electricity
• Greater power rating means the appliance uses more energy
• Power rating of an appliance shows the power it uses in Watts
• Positive and negative charges exist
• Electric Fields are for charges, pointing in the direction a positive charge would go
• Charge

  A property of all matter
• Current

  Measured in amperes A
• All the electrical energy (ideally) gets transferred to the appliance
• Sparking occurs when enough charge builds up and objects are close but not touching