7.3 - Efficiency (Energy & Power)

• What can energy be transferred into?

  Different forms of energy
• Why are most devices not 100% efficient?

  Because energy is lost in the process
• What is efficiency in terms of energy transfer?

  • Proportion of input energy converted to useful output
  • Useful energy output vs. total energy input
• What type of energy does a lamp convert its input energy into?

  Light energy and heat energy
• How is useful energy output defined for a lamp?

  As the light energy produced
• What is the formula for calculating efficiency?

  Efficiency = useful energy output / total energy input
• How do you calculate efficiency using power?

  Efficiency = useful power output / total power input
• If a lamp has an input of 300 joules and outputs 45 joules of light, what is its efficiency?

  0.15
• If a lamp has an input of 300 joules and outputs 225 joules of light, what is its efficiency?

  0.75
• How many times more efficient is the LED lamp compared to the incandescent bulb?

  5 times more efficient
• How do you convert efficiency from decimal to percentage?

  Multiply by 100
• What is the efficiency of the incandescent bulb in percentage terms?

  15 percent
• What is the efficiency of the LED bulb in percentage terms?

  75 percent
• What happens if you get the division wrong when calculating efficiency?

  You get a value greater than one
• What does an efficiency rating of 133 percent imply?

  More energy output than input
• What principle states that energy can only be transferred?

  Conservation of energy principle
• If a microwave is 70% efficient with a total power input of 800 watts, what is the useful power output?

  560 watts
• What is the common waste energy produced by devices?

  • Thermal energy
  • Often considered non-useful output
• What is an exception to the rule of efficiency in devices?

  • Devices designed to produce heat
  • Example: Electric heaters