Phy 132 – Assignment 13
A.
B. 1. a. Hold a piece of metal over a flame, or put an egg in a hot frying pan, or
… (There are thousands of possible answers.)
b. Put an ice cube in a hot frying pan. (If kept well stirred, the ice/water
mixture stays at 0°C until completely melted. As energy is added, the internal
energy goes up, but the molecules are not gaining kinetic energy, so the
temperature stays the same. Rather, the energy goes into breaking bonds
between molecules, increasing a form of potential energy.)
2.
C.
D. 1. a. One of many possible answers: Start a fire by rubbing two sticks
together. The work done by friction, not heat flow, raises a stick’s internal
energy and its temperature.
b. Ride in an elevator. Work is done on you as you are lifted, but it increases
an external form of energy, having no effect on internal energy or temperature.
2.
E. 1. a. -100 J: ΔEint = Q + W. Q = 0 is the definition of the word adiabatic.
(No heat flow.) There is 100 J of work, and W is negative when work is done
by the gas. Or, think of the sign this way: As the gas expands, it gives energy
to the outside world, perhaps turning the wheels of a car. Since energy is
flowing out, the internal energy must be decreasing, and Δ(anything) is positive
for an increase, negative for a decrease.
b. 0 J: ΔEint = nCVΔT. ΔT = 0 is what the word isothermal means. (No
temperature change.)
2.
F.