Energy Efficiency You can’t get something for nothing!

Efficiency  Nothing can ever be 100% efficient  There is always some energy lost due to frictional (dissipative) forces  This is usually lost as heat, which is difficult to reclaim  Typical efficiencies of electrical turbines are usually 25-33%.

Efficiency  The incandescent light bulb is about % efficient at converting electrical energy into light.  The rest is lost as thermal energy.  The CFL (spiral light bulb) is typically 9- 11% efficient  The LED light bulb is 4 times as efficient as incandescent lights.

Efficiency

Example  A family uses several planks to slide a 350. kg piano onto the back of a pickup truck. The box at the back of the pickup is 81 cm above the ground. The planks are 3.0 m long N is used to move the piano up the planks. a)Find the work done in loading the piano. b)Calculate the efficiency to load the piano. c)Where does the rest of the energy go?

Example Solved a) W = F●d = (1500 N)(3.0m) = 4.5 x 10 3 J b) E out is gravitational potential energy. E g = mgh = 350 kg(9.81 m/s 2 )(0.81 m) = J e = E out /E in = J/4500 J = 0.62 = 62%

Where did the energy go?  The lost energy from friction, as the piano slides along the planks, is transformed into i)thermal energy ii)sound energy (the piano sliding along the wood).

Perpetual Motion?  