Question

Question 27 (3 points)
If P equals an amount of energy, which equation correctly expresses n, or energy
efficiency?
A. n=P out + P in
B. n- Pout - Pin
C. n = P out / P in​

Answer 1

Answer:

C. n = P out / P in

Explanation:

Efficiency, in terms of energy, is generally defined as the amount of useful energy in output from a system divided by the amount of energy in input needed to make the system working.

Mathematically:

$\eta = \frac{E_{out}}{E_{in}}$

Or, since in our problem the energy is labelled with P,

$\eta = \frac{P_{out}}{P_{in}}$

No machine can have an efficiency of 1.0 (100 %), because not all the energy in input can be converted into useful output energy: part of it, in fact, is wasted because of internal frictions, and converted into thermal energy (heat).