Electrical Energy and Power

• How is power defined in mechanics?

  As the rate of doing work

  
• What does potential difference represent?

  Work done per unit charge
• What is current defined as?

  The rate of flow of charge
• How is electrical power defined?

  As the rate of change of work done

  
• What does the power in an electrical component represent?

  Energy transferred per second
• How can power dissipated by an electrical device be expressed?

  Using Ohm's Law and resistance
• If the current or voltage doubles in a resistor, how does the power change?

  It becomes four times as great
• What determines which power equation to use in a problem?

  The given value of current or voltage
• What is the equation for energy transferred in terms of voltage, current, and time?

  E = VIt
• What does E represent in the equation E = VIt?

  Energy transferred (J)
• What does V represent in the equation E = VIt?

  Voltage (V)
• What does I represent in the equation E = VIt?

  Current (A)
• What does t represent in the equation E = VIt?

  Time (s)
• What happens when two lamps are connected in series to a 150 V power supply?

  • Both lamps light normally
  • The 15 V lamp does not blow
  • Both lamps light at normal brightness

  
• What mnemonic can help remember the power equations?

  “Twinkle Twinkle Little Star, Power equals I squared R”
• What is the unit of electrical power?

  Watts (W)
• Why should time be in seconds when calculating electrical power?

  Because the unit of power is Watts