Efficiency

• What is the main topic discussed in the video?

  The efficiency of energy transfer in devices
• Why is energy not always transferred into the intended form?

  Most devices are not 100% efficient
• What is considered useful energy output for a lamp?

  Light energy
• How is the efficiency of a device defined?

  As the proportion of input energy that is converted to useful output
• How do you calculate the efficiency of a device using energy?

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

  Efficiency = useful power output / total power input
• What is the efficiency calculation process for two lamps with different bulbs?

  1. Calculate efficiency for each bulb:

  • Incandescent: \( \text{Efficiency} = \frac{45 \text{ joules}}{300 \text{ joules}} = 0.15 \)
  • LED: \( \text{Efficiency} = \frac{225 \text{ joules}}{300 \text{ joules}} = 0.75 \)

  1. Compare efficiencies: \( \frac{0.75}{0.15} = 5 \)
• What is the efficiency of the incandescent bulb in decimal form?

  0.15
• What is the efficiency of the LED bulb in decimal form?

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

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

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

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

  75%
• What is a common mistake when calculating efficiency?

  Getting the division the wrong way around
• What happens if you calculate efficiency incorrectly and get a value greater than 1?

  It implies more energy output than input, which is impossible
• What principle explains why energy cannot exceed input in efficiency calculations?

  The conservation of energy principle
• How do you calculate the useful power output of a microwave with 70% efficiency and 800 watts input?

  1. Convert efficiency to decimal: \( 70\% = 0.7 \)
  2. Use the efficiency equation:

  • \( \text{Useful Power Output} = 0.7 \times 800 \text{ watts} = 560 \text{ watts} \)
• What is the efficiency of the microwave discussed?

  70%
• What is the useful power output of the microwave with 800 watts input?

  560 watts
• Why are most devices not 100% efficient?

  They produce some form of waste energy
• What is an exception to the rule of devices not being 100% efficient?

  Devices designed to produce heat, like electric heaters