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 formula for calculating energy transferred in joules?

  Energy transferred \( E = P \times t \)
• How do you calculate the energy transferred when a current of 0.7 A passes through a potential difference of 4 V for 1 minute?

  Use \( E = I \times V \times t \) to find \( E = 0.7 \times 4 \times 60 = 168 \text{ J} \)
• What is the power rating of an appliance?

  • The amount of energy it transfers by electrical work every second
  • Given on a label including voltage, frequency, and power rating in Watts

  
• What is the consequence of plugging an appliance into a mains supply with a much higher voltage than stated?

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

  A system of cables and transformers linking power stations to consumers
• What do step-up transformers do in the National Grid?

  They increase the voltage and reduce the current

  
• Why is the National Grid efficient?

  It uses step-up and step-down transformers to minimize energy loss

  
• How does increasing the potential difference affect energy dissipation in wires?

  High potential difference means low current, resulting in less energy dissipated
• What is the role 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