Electricity

• What is the definition of current?

  Flow of electrical charge
• What is the unit of current?

  Ampere, A
• What is potential difference?

  Driving force that pushes charge round
• What is the unit of potential difference?

  Volt, V
• What is resistance?

  Anything that slows down charge flow
• What is the unit of resistance?

  Ohm, W
• What does the equation $Q =$$It$ represent?


  Charge is the product of current and time
• What happens to current if there is no source of potential difference?

  No current flows
• How does resistance affect current?

  The greater the resistance, the smaller the current
• What is the relationship between potential difference and current for a fixed resistance?

  The greater the potential difference, the larger the current
• What is the potential difference equation?

  $V =$$IR$
• What are the circuit symbols for common components?

  • Cell
  • Battery
  • Switch (open and closed)
  • Resistor
  • Variable resistor
  • Filament lamp
  • Ammeter
  • Voltmeter
  • Diode
  • LDR (Light-Dependent Resistor)
  • Thermistor
  • LED (Light-Emitting Diode)
  • Fuse
• What characterizes an ohmic conductor?

  Current is directly proportional to potential difference
• What happens to the resistance of a filament lamp as current increases?

  Resistance increases as temperature of filament increases
• How does a diode function in a circuit?

  High resistance in one direction, allowing current in the other
• What are the characteristics of series circuits?

  • Total resistance: $R_{total} =$$R_1 +$$R_2$
  • Current is the same everywhere: $I_{total} =$$I_1 =$$I_2$
  • Total potential difference is shared: $V_{total} =$$V_1 +$$V_2$
• What are the characteristics of parallel circuits?

  • Total resistance is less than the smallest resistor
  • Adding a resistor decreases total resistance
  • Total current is the sum of currents through each branch: $I_{total} =$$I_1 +$$I_2$
  • Potential difference across each branch is the same
• What are the three wires in a three-core cable?

  Live wire, neutral wire, earth wire
• What is the potential difference of the live wire in the UK mains electricity?

  230 V
• What is the frequency of the UK mains electricity supply?

  50 Hz
• What happens if there is a fault in the earth wire?

  Current only flows through earth wire
• What is the definition of power in electrical terms?

  Energy transferred per second
• What is the power rating of an appliance?

  Maximum safe power an appliance can operate at
• How is energy transferred in electrical systems?

  Energy transferred electrically to thermal or kinetic energy stores
• What is the National Grid?

  • System of cables and transformers
  • Connects power stations to consumers
  • Transfers electrical power efficiently
• Why is transferring power at high current inefficient?

  It heats up wires and wastes energy
• What happens when two insulating materials are rubbed together?

  Electrons move, creating static charge
• What is an electric spark?

  Passage of electrons across a gap
• What are the steps to create an electric spark?

  Charge builds, potential difference increases, spark occurs
• What are the characteristics of electric fields around charged objects?

  • Charged objects feel a force in each other's fields
  • Non-contact forces
  • Stronger fields have closer field lines
  • Electric fields can ionize air particles
• What happens to the force between charged objects as distance decreases?

  The force acting on the charges increases
• What is the definition of an electric field?

  Region where another charged object feels a force
• What occurs during attraction and repulsion in electric fields?

  Like charges repel, opposite charges attract
• How do electric fields affect air particles?

  Strong electric fields can ionize air particles