Energy Transfers and Efficiency

An open system is...

• an object with a hole in it

• an object which gains or loses energy

• an object which does not let energy in or out

• an object that is outside

Almost all objects lose energy in the form of __________.

Select the correct equation:

• $Efficiency\ =\ \frac{useful}{wasted}\times100$

• $Efficiency\ =\ \frac{wasted}{useful}\times100$

• $Efficiency\ =\ \frac{wasted}{input}\times100$

• $Efficiency\ =\frac{useful}{input}\times100$

A __________ diagram shows the energy transfers in a system.

What is the value of the wasted energy?

As a percentage, what is the efficiency of the bulb represented by the Sankey diagram?

What type of energy is useful?

Which bulb is the most efficient?

• Filament bulb

• LED light

• CFL lamp

A device transfers 600 J of electrical energy into 350 J of useful sound energy. Calculate the efficiency of the device to 2 significant figures.

A bulb is 70% efficient. It produces 49 J of light energy. How much energy is inputted?