Power and efficiency

[P] = 1 Watt (= 1 horsepower)

Understanding power:

a conversion of electric energy to thermal energy and radiation energy (light + heat)

efficiency (example Prezi lamp) = 7% (that’s useful) → 100J electric energy, 7J light and 93J heat

100W; 100J of energy is converted per second. (Meaning of power)

The lamp does 100J of work per second

heat = energy lost to the environment

^^P = delta E / delta t^^ = W / delta t (with delta t standing for energy per second)

<<Power = the amount of energy that is converted per second/ + the amount of work done per second (exam question)<<

100000 W = 100 kW

Exercise:

F* delta x / delta t = Fg * delta x / delta t = m*g delta x / delta t = 8,7 **10³ kg*9,81/delta t = 1710(to the fourth) W

Efficiency:

^^η = E useful / E total (for %: *100) (eta)^^

→ when given 20% write 20/100

E total = E k / 0.20 = (m * v²) /2 = (375000) /0.20 = 19*10 to the 6th

→ don’t forget to divide by 3.6 en 0.20

Exercise: E useful (gravitational potential) = m*g*h = (176580)

(176580)/0.200*10 to the sixth = (0.8829) = 0.88 J → 88%

Exercise 2: P = E pg / delta t = m*g*h/ delta t = (549360)/200W (P)= (2746.8) = 27*10² s

sustainable energy → there for next generations and good for the climate (not environment)

dissipation, energy lost because of the unusable form → heat