Energy Transfers

• What is electrical power defined as?

  The rate of energy transfer or the amount of energy transferred per second
• What factors does the power of a device depend on?

  The voltage and current of the device
• What is the formula for electrical power?

  P = VI

  
• What is the unit of power and how is it defined?

  • The unit of power is the watt (W)
  • 1 watt is equivalent to 1 joule per second (J/s)
• How do you calculate the potential difference through a device if you know its power and current?

  Use the equation \( V = \frac{P}{I} \)

  
• What is the relationship between voltage, current, and resistance in an electric device?

  The voltage across an electric device depends on the current and resistance of that device

  
• How can power be expressed in terms of resistance?

  Power can be written as \( P = I^2 R \)

  
• How do you calculate the power through a resistor if you know its resistance and current?

  Use the equation \( P = I^2 R \)

  
• What is the energy transferred by electrical work in a component dependent on?

  The current, potential difference, and time the component is used for
• What is the equation for calculating energy transferred?

  Energy transferred \( E = P \times t \)
• How can the energy transferred also be expressed using current and potential difference?

  As \( E = I \times V \times t \)
• What does the equation \( E = Q \times V \) represent?

  The energy transferred depends on charge and potential difference

  
• What happens when charge flows around a circuit?

  The energy transferred from the cell or battery equals the energy transferred to all components in the circuit
• What is the power rating of an appliance?

  The amount of energy it transfers by electrical work every second
• What information is typically included on the power rating label of an appliance?

  The potential difference, frequency of supply, and power rating in watts
• Why is it important not to plug an appliance into a mains supply with a much higher voltage than stated?

  It could cause the appliance to fuse or catch fire
• What does the National Grid do?

  It distributes electricity across the UK
• What are the two types of transformers used in the National Grid?

  Step-up transformers and step-down transformers
• How do step-up transformers increase the efficiency of the National Grid?

  By increasing voltage and decreasing current, reducing energy loss due to heating

  
• What type of current is produced in power stations?

  Alternating current (AC)
• What is the function of transformers in the National Grid?

  To increase and decrease the potential difference of the current
• What distinguishes a step-up transformer from a step-down transformer?

  A step-up transformer has more turns on the secondary coil than the primary
• What is the purpose of a step-down transformer?

  To decrease the potential difference for domestic use