Physics 18 clickers

Entropy can be:

created, and conserved, but not destroyed.

The greater the difference in temperature between the input reservoir and the output reservoir for a heat engine, the:

greater the efficiency. The pressure and Temperature are proportional. Greater temperature = greater pressure. Better efficiency

More efficient gasoline engines can be built if:

materials are developed that can withstand higher temperatures. Melting point of engine materials limits the upper temperatures at which they can operate. Ceramic engines would be better!

Systems that are left alone, tend to move toward a state of:

more entropy. Few exceptions, but greater entropy occurs with time. Energy transforms from one form to another directed toward greater disorder.

During an adiabatic compression of an ideal gas:

no heat enters or leaves the system. Internal energy changes are equal to the work done on/by the the system. Work ON system: IE increases (tire pump warms up). Work BY system: IE decreases (valve cools off).

During an isothermal compression of an ideal gas:

*air temperature* rises as pressure is increased, or as heat is added. This does not mean *internal energy*. work is done on the system, as result of compression, the volume will decrease, and temperature will try to increase. To maintain the temperature at constant value (as the process is isothermal) heat energy has to leave the system and enter the environment. The amount of energy entering the environment is equal to the work done (by compressing the perfect gas) because internal energy does not change. The thermodynamic sign convention is that heat entering the environment is also negative. Thus -Q = W.

The amount of chemical energy ultimately converted to heat by an automobile is about:

100% ultimate actual efficiency (it will all eventually be transformed into heat!), as opposed to 50% ideal efficiency.

Is it possible to wholly convert a given amount of heat energy into mechanical energy?

No. The 2nd law of thermodynamics says no heat engine can convert all the heat supplied into mechanical energy. Only some heat is transformed into work, with the rest expelled in the process.

It is possible to totally convert a given amount of mechanical energy into heat.

True. *Pushing a heavy crate across a rough floor: all the work goes into heating the floor and crate. Work against friction produces heat.

If you run a refrigerator in a closed room with the refrigerator door open, the room temperature will:

remain unchanged. By pumping out the heat from its interior, the fridge lowers its internal temperature and raises the room's temperature outside. Opening the door will circulate hot and cold air, equalizing everything.

The first law of thermodynamics is a restatement of

the conservation of energy, including heat. When heat flows to or from a system, the system gains or loses an amount of energy equal to the amount of heat transferred.

When a volume of air is compressed and no heat enters or leaves, the air temperature will:

will increase (adiabatic compression) no heat enters or leaves system; work is done *on* the system by compression.