Electrical Power and Energy

• Why is understanding electrical power and energy important in GCSE Physics?

  It is crucial for grasping how electrical systems work and how energy is used in various applications.
• What is the definition of electrical power?

  • Electrical power is the rate at which electrical energy is transferred or converted into another form of energy.
  • Measured in watts (W).
• What is the formula for electrical power?

  $P =$$V \times I$
• What do the variables in the power formula represent?

  $P =$$\text{Power (W)}, V =$$\text{Voltage (V)}, I =$$\text{Current (A)}$
• What is one watt defined as?

  One joule of energy transferred per second.
• How can power be expressed in circuits with resistors?

  1. \(P = I^2 \times R\)
  2. \(P = \frac{V^2}{R}\)

  • Where \(R\) is resistance in Ohms (Ω).
• What is the definition of electrical energy?

  Energy consumed by electrical devices or produced by electrical systems over time.
• What is the formula for electrical energy?

  $E =$$P \times t$
• What do the variables in the energy formula represent?

  $E =$$\text{Energy (J)}, P =$$\text{Power (W)}, t =$$\text{Time (s)}$
• How do you convert energy to kilowatt-hours?

  $E (\text{kWh}) =$$\frac{P (\text{kW}) \times t (\text{h})}{1000}$
• What is the power consumed by a device that operates at 120V and draws a current of 3A?

  360W
• How much energy does a heater that consumes 1500W of power use for 2 hours?

  10,800,000J or 10.8 MJ
• What is efficiency in the context of electrical devices?

  • Efficiency measures how much of the electrical energy supplied is converted into useful energy output.
  • Expressed as a percentage.
• What is the formula for calculating efficiency?

  $\text{Efficiency} (\%) =$$\left( \frac{\text{Useful Power Output}}{\text{Total Power Input}} \right) \times 100$
• What are some practical applications of understanding electrical power and energy?

  • Home appliances: Calculating energy consumption and costs.
  • Renewable energy: Evaluating energy efficiency in solar panels and wind turbines.
  • Electric vehicles: Understanding power used in charging and energy efficiency of motors.
• What is the summary of electrical power and energy concepts?

  • Electrical Power: Rate of energy transfer, calculated as \(P = V \times I\).
  • Electrical Energy: Total energy consumed over time, calculated as \(E = P \times t\).
  • Efficiency: Assesses how effectively devices use energy.
• What is the power consumed by a device that operates at 240V and has a current of 2.5A?

  $P =$$240V \times 2.5A =$$600W$
• How much energy does a light bulb using 60W of power for 5 hours consume in kilowatt-hours?

  $E =$$60W \times (5 \text{ hours} \times 3600 \text{ seconds/hour}) =$$1080 \text{ Wh} =$$1.08 \text{ kWh}$
• If a resistor has a resistance of 8Ω and carries a current of 4A, what is the power dissipated in the resistor?

  $P =$$I^2 \times R =$$4A^2 \times 8Ω =$$128W$
• If a kettle with a power rating of 3000W is used for 10 minutes, how much energy does it consume in kilowatt-hours?

  $E =$$3000W \times (10 \text{ minutes} \times 60 \text{ seconds/minute}) =$$1800000 \text{ J} =$$0.5 \text{ kWh}$
• If an appliance has a total power input of 1000W and outputs 800W of useful energy, what is its efficiency?

  $\text{Efficiency} (\%) =$$\left( \frac{800W}{1000W} \right) \times 100 =$$80\%$