Electricity | AQA GCSE Physics Notes | Topic 2

AQA GCSE Physics Notes for Topic 2 - Electricity, guaranteed to get you a GRADE 9

  • Cells: provide voltage. Pushes charge
  • Batteries: two or more cells.
  • Open switch: off
  • Closed switch: on (connected)
  • Resistor: controls current to a certain level.
  • Variable Resistor: this can be adjusted manually.
  • Diode: only allows current to flow in one direction (high resistance backwards).
  • Ammeter: measures current (connect in series).
  • Voltmeter: measures potential difference (connect in parallel).
  • Thermistor: as temperature increases, resistance decreases automatically (thermostats)
  • LDR: as light intensity increases, resistance decreases automatically (street lamps)
  • Current: rate of flow of charge.
  • Q = It
  • Q: charge (C), I: current (A), t: time (s)
  • V = IR
  • V: potential difference (V), I: current (A), R: resistance (Ω)
IV Graph for Fixed Resistor
  • In a fixed resistor, resistance is constant, so the I-V graph is a straight line.
IV Graph for Filament Lamp
  • In a filament lamp, resistance increases as the lamp gets hot, so the current slows down.
IV Graph for Diode
  • In a diode, current doesn't flow backwards so the I-V graph doesn't go down.
  • Series Circuits: (one loop). Current is the same everywhere. Voltage adds up to battery. Resistance adds up.
  • Parallel Circuits: Voltage is the same everywhere. Current adds up from each branch.
  • Mains electricity is an ac supply. In the United Kingdom, the domestic electricity supply has a frequency of 50 Hz and is about 230 V.
  • Live wire: brown. Carries the alternating potential difference from the supply.
  • Neutral wire: blue. Completes the circuit.
  • Earth wire: green and yellow. Safety wire to stop the appliance becoming live.
  • P = IV
  • P = I2R
  • E = Pt
  • E = QV
  • P: Power (W), E: Energy (J)
  • The National Grid is a system of cables and transformers linking power stations to consumers.
  • Step-up transformers are used to increase the potential difference from the power station to the transmission cables. (P = IV so a high V allows I to be low. If I was high, that would cause heated wires, which is inefficient.
  • Step-down transformers are used to decrease the V for homes to use.

Triple Science Only

  • When certain insulating materials are rubbed against each other they become electrically charged. Negative electrons are rubbed from one material to the other.
  • When two charged objects are brought close together they exert a force on each other. Like charges repel. Opposite charges attract. These are non-contact forces.
  • A charged object creates an electric field around itself. The electric field is strongest close to the charged object. A second charged object placed in the field experiences a force. The force gets stronger as the distance between the objects decreases.