Department of Natural Sciences
Clayton State University
Morrow, Georgia

January 29, 2009

SCI 1901E - Quiz 3

Name _________SOLUTION____________

(07)    1.         A coal-fired power plant produces electricity.  The electricity is then transmitted by power lines to users, and finally used to provide electrical power to a variety of devices.

a.       If 1.00 J of chemical energy is used in burning coal for every 0.360 J of electrical energy produced, calculate the efficiency of the power plant for the production of electricity from burning coal.

e = (useful energy output / energy input ) x 100%

e_coal = (electrical energy output / chemical energy of coal input) x 100%

e_coal = (0.360 J)/(1.00 J) x 100%

e_coal = 36.0 %_ANS

b.         If 10.0% of the electrical energy that leaves the power plant is lost in itstransmission to a particular user, what is the efficiency
                                for transmission?

If 10.0%  is lost, then 90.0 % is transmitted.  Therefore,

e_trans = 90.0 %

c.         If the user runs an electric motor with an efficiency of 80.0% using th electrical energy transmitted to it, calculate the efficiency
                                of the overall process that began with the burning of coal at the power plant.

e_motor = 80.0 %

e_tot = e_coal e_trans e_motor

e_tot = (0.36)(0.90)(0.80) = 0.2592

e_tot = 25.9%

Circle the single best answer in question 2.

(04)     2.         In an isolated or closed system,

a.         Mechanical energy is always conserved.

b.         No work is done on the system and no heat is added to the system.

c.         Heat energy may flow into or out of the system.

d.         The thermal energy of the system cannot change in time.

(04)     3.         Explain what is meant by “sustainable development.”

                        Development which meets the needs of the present without compromising the ability of future generations to meet their own needs.