Electricity science

• What is electric current?

  Electric current is the flow of electric charge.
• What units are charge, current, and time measured in?

  Charge is measured in coulombs, current in amperes, and time in seconds.
• What is the same at all points when charge flows in a closed loop?

  The electric current is the same at all points in a closed loop.
• What must there be in a closed circuit so that electrical charge can flow?

  There must be a complete path for the electrical charge to flow.
• Which two factors does current depend on and what are their units?

  Current depends on voltage (volts) and resistance (ohms).
• What happens to the current if the resistance is increased but the potential difference stays the same?

  The current decreases if the resistance is increased while the potential difference remains constant.
• What is an ohmic conductor?

  An ohmic conductor is a material that follows Ohm's law, where current is directly proportional to voltage.
• What happens to the resistance of a filament lamp as its temperature increases?

  The resistance of a filament lamp increases as its temperature increases.
• What happens to the resistance of a thermistor as its temperature increases?

  The resistance of a thermistor decreases as its temperature increases.
• What happens to the resistance of a light-dependent resistor when light intensity increases?

  The resistance of a light-dependent resistor decreases as light intensity increases.
• What are the main features of a series circuit?

  • Current is the same through all components
  • Total voltage is the sum of the voltages across each component
  • If one component fails, the entire circuit is broken
• What are the main features of a parallel circuit?

  • Voltage is the same across all components
  • Total current is the sum of the currents through each component
  • If one component fails, the rest can still operate
• Why is the current provided by a cell called a direct current (d.c.)?

  The current provided by a cell is called direct current (d.c.) because it flows in one direction only.
• What is an alternating current (a.c.)?

  Alternating current (a.c.) is an electric current that reverses direction periodically.
• What kind of current is supplied by mains electricity?

  Mains electricity supplies alternating current (a.c.).
• What is the frequency and voltage of mains electricity?

  The frequency of mains electricity is 50 Hz and the voltage is typically 230 V.
• What colours are the live, neutral, and earth wires in a three-core cable?

  The live wire is brown, the neutral wire is blue, and the earth wire is green/yellow.
• What is the function of the live wire in a three-core cable?

  The live wire carries the current to the appliance.
• What is the function of the neutral wire in a three-core cable?

  The neutral wire completes the circuit by carrying current away from the appliance.
• What is the function of the earth wire in a three-core cable?

  The earth wire provides a safety path for current to prevent electric shock.
• When is there a current in the earth wire?

  There is a current in the earth wire when there is a fault in the appliance.
• Why is the live wire dangerous?

  The live wire is dangerous because it carries a high voltage that can cause electric shock.
• What is the National Grid?

  The National Grid is a system for distributing electricity across a country.
• What are step-up transformers used for in the National Grid?

  Step-up transformers are used to increase the voltage for efficient transmission of electricity.
• What are step-down transformers used for in the National Grid?

  Step-down transformers are used to decrease the voltage for safe distribution to consumers.
• How does having a large potential difference in the transmission cables help to make the National Grid an efficient way to transfer energy?

  A large potential difference reduces energy loss as heat during transmission.
• What two things does energy transfer to an appliance depend on?

  Energy transfer to an appliance depends on power and time.
• What are the units for power, current, potential difference, and resistance?

  The units are watts for power, amperes for current, volts for potential difference, and ohms for resistance.