P7.2 Power and Efficiency

• The units of power are watts
• The units of energy efficiency are percent
• Match the concept with its description:

  Energy Transferred ↔️ The amount of energy that changes from one form to another per unit time.

  Work Done ↔️ The amount of work done per unit time.

  Units of Power ↔️ Watts (W) or Joules per second (J/s)
• Match the concept with its description:

  Energy Transferred ↔️ The amount of energy that changes from one form to another per unit time.

  Work Done ↔️ The amount of work done per unit time.

  Units of Power ↔️ Watts (W) or Joules per second (J/s)
• Why is the unit of power the watt (W)?

  It measures energy transfer rate
• Power measures the rate of energy transfer or work done per unit time.


  True
• The watt is equivalent to the work done in one second.


  True
• Energy efficiency is the ratio of useful energy output to total energy input.


  True
• Applying power and efficiency concepts is relevant to real-life examples.

  True
• Power is the rate at which energy is transferred or work is done
• What is the unit of power?

  Watt (W)
• What is the formula for power?

  $P =$$\frac{W}{t}$
• What does the symbol $W$ stand for in the power formula?


  Work done
• Match the concept with its definition or formula:

  Energy Transferred ↔️ The amount of energy that changes from one form to another per unit time

  Work Done ↔️ The amount of work done per unit time
• What is the formula for calculating energy efficiency?

  $\frac{E_{useful}}{E_{total}} \times 100 \%$
• Power measures how efficiently work is completed or how quickly energy changes form.


  True
• Energy efficiency is the ratio of useful energy output to the total energy input.


  True
• What is the relationship between power and joules per second?

  1 W = 1 J/s
• If 100 joules of work are done in 5 seconds, what is the power in watts?

  20 W
• Calculate the power if 100 joules of energy are transferred in 5 seconds.

  20 watts
• How much energy does a 60W light bulb consume per second?

  60 joules
• What is the definition of total energy input in the context of energy efficiency?

  Total energy entering the system
• Efficiency is expressed as a percentage.


  True
• Power measures the rate at which work is done or energy is transferred.


  True
• What does 't' represent in the formula for power?

  Time
• What is the formula for power in terms of work done?

  $P =$$\frac{W}{t}$
• What does 'P' represent in the formula for power?

  Power
• What is one watt equivalent to?

  Joules per second
• Energy efficiency is expressed as a percentage
• A refrigerator uses 600 J of electricity to produce 450 J of cooling. Its efficiency is 75%
• What does it mean if a solar panel has an efficiency of 40%?

  40% of solar energy converts to electricity
• Match the component with its symbol, definition, and units:

  Energy Input ↔️ $E_{\in}$ ||| Total energy supplied to the system ||| Joules (J)

  Energy Output ↔️ $E_{out}$ ||| Energy used for the intended purpose ||| Joules (J)

  Efficiency ↔️ % ||| Ratio of useful energy output to total energy input, expressed as a percentage ||| %
• Power is the rate at which energy is transferred or work is done.

  True
• If 100 joules of work are done in 5 seconds, the power is 20 watts.
• Match the example with its calculated power and energy efficiency:

  Gasoline-Powered Car ↔️ 4.2 kW ||| 30%

  LED Light Bulb ↔️ 16 W ||| 80%

  Solar Panel ↔️ 0.556 kW ||| 20%
• The unit of power is the watt (W), which is equivalent to joules per second.
• One watt represents the amount of energy transferred or work done in one second.
• The unit of power is the watt, which is equivalent to joules per
• Using watts helps us understand the energy usage of appliances and compare their efficiency
• The formula for energy efficiency is useful energy output divided by total energy input, multiplied by 100%.