Topic 10 + 11 - Electricity

• Subatomic Particles

  • Proton
  • Neutron
  • Electron
• Electricity Circuits

  1. Series Circuits: Closed circuit, The current is the same everywhere

  2. Parallel Circuits: Branched circuit, Current splits into multiple paths, Total current into a junction = total current in each of the branches, Voltage is the same across each “branch”
• Potential Difference

  Energy transferred per unit charge, Measured in Volts, Energy transferred (joule, J) = charge moved (coulomb, C) × potential difference (volt, V)
• Resistance

  Greater resistance means harder for charge to flow through the component, Variable resistor changes the amount of resistance of the component
• Series Components

  Connected end to end, All the current flows through all the components, Can only switch them all off at once, PD 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
• Parallel Components

  Connected separately to the power supply, Current flows through each one separately, You can switch each component off individually, PD 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
• Static Electricity

  A property of all matter
• Positive and negative charges

  If a body has the same amount of positive and negative charge, they cancel out, forming a neutral body
• Like Charges

  Repel
• Opposite charges

  Attract
• Insulators do not conduct electricity
• Insulators

  Their electrons cannot flow throughout the material, they are fixed
• Conductors can conduct electricity
• Conductors

  Their electrons can flow, and are not fixed (they are delocalised)
• Charging by friction

  When two insulators are rubbed together, electrons are transferred from one object to the other, forming a positive charge on one object and a negative charge on the other
• Sparking

  Occurs when enough charge builds up, and the objects are close but not touching. The charge jumps through the air from the highly negative object to the highly positive object to balance out the charges
• Lightning

  Occurs when the charge difference between clouds and the Earth becomes so great, and a massive spark (lightning) jumps across to balance the charge
• Forces exerted

  The charged objects experience a force called electrostatic force of attraction/repulsion. Greater charge or closer distance results in a greater force
• Earthing

  Allows electrons to flow to the earth, removing excess charge and allowing materials to stay neutral
• Insecticide sprays

  Are sprayed from aircraft with a charge, causing the spray droplets to repel each other, spread evenly, and be attracted to the earth
• Dangers of Sparks

  If charge builds up and a spark forms when fuelling cars, it could ignite and cause a massive explosion. Hoses are earthed to prevent this
• Electric Fields

  Similar to magnetic fields for magnets, electric fields are for charges. They point in the direction a positive charge would go, away from positive charges and towards negative charges
• Parallel circuits

  • Charge can only pass through any one branch
  • Current is shared between each of the branches
  • Current through source is the sum of current through each branch
  • Total resistance is less than the branch with the smallest resistance
  • Two resistors in parallel will have a smaller overall resistance than just one
• Parallel circuits

  Because charge has more than one branch to take, only some charge will flow along each branch
• As current increases, electrons (charge) has more energy
• When electrons flow through a resistor, they collide with the ions in the resistor
• The current through a resistor does work against the resistance, transferring energy to the ions, causing them to vibrate more (heating resistor)
• Resistance increases and current decreases as electrons collide with ions and resistance increases
• Some appliances like a toaster use heating filaments with high resistance to get hot easily
• With temperature, normal wires experience the same process as atoms vibrate when hot
• Thermistors have lower resistance at hotter temperatures and are used in temperature detectors/thermostats
• Greater length of wire results in more resistance and lower current
• Thinner wires have greater resistance due to less room for electrons to pass through between atoms
• LDR (Light Dependent Resistor) has lower resistance with greater light intensity and is used in automatic night lights
• Diodes allow current to flow freely in one direction and have very high resistance in the opposite direction
• Efficiency is improved with low resistance wires to reduce energy loss as current flows through the circuit
• Gradient of each website is 1/resistance, so a sharper gradient means lower resistance
• Testing Relationships

  1. Make sure components do not overheat, leave to cool down between each reading

  2. Repeat and take average

  3. Varied wire resistance testing: wires ranging from 1Ω to 10Ω connected to different DC voltages, measure current for each voltage, plot a graph

  4. Filament lamps testing: connected to different DC voltages, measure current for each voltage, plot a graph

  5. Diodes testing: connected to different DC voltages, measure current for each voltage, switch diode direction to record current for negative voltages, plot graphs for positive and negative potential differences
• Open switch


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• Closed switch


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