Experiment 12: Heat and Temperature
(Also look at lab 13 today: You need to get data ahead of time, which you should start to plan for.)
Fill your steam generator about two-thirds full of warm water and set it on the hot plate, turned all
the way up. DO THIS IMMEDIATELY BECAUSE YOU WILL HAVE TO WAIT FOR IT TO
BOIL. Do not let it boil dry, or let the hose touch the hot plate. DO NOT PUT THE
THERMOMETER IN IT; electronic thermometers don't like being steamed. Gloves and tongs for
handling hot objects are available if you want them.
Part 1: Specific Heat
You will measure the specific heat of a piece of metal. The masses of the metal and a cup of water
are measured. The metal is then heated by boiling water. Once hot, the metal is placed in the cup of
room temperature water. The temperature in the cup is measured before and after adding the hot
metal. The specific heat is calculated from the idea that the heat gained by the water equals the
(negative of) the heat lost by the metal.
1. Measure the metal’s mass and note the kind of metal it is. Mass a pair of Styrofoam cups, one
inside the other. (Two cups for a little extra insulation.) Fill the inner cup about half full of water,
find the total mass of the cups and water and subtract to get the water’s mass.
2. While waiting for the water to boil, put the metal in the steam generator with the string hanging
out. If the metal has been in the water a few minutes when it reaches a boil, the metal is ready to go.
Either leave the cork off or have the hose’s end in a beaker so the table won’t get wet.
3. Measure the temperature of the water in the Styrofoam cup just before putting the metal in it, to
the nearest tenth of a degree.
4. Hold the cup right next to the boiling water and quickly transfer the hot metal into the cold water.
(Heat escapes into the air very rapidly.) Stir it a lot with the thermometer. Record the highest
temperature the water reaches. (It will rise for a minute or so as it gains heat from the metal, then
slowly drop as heat is lost to the air.)
Calculations: Set ΣQ equal to zero. The only unknown in this equation will be the metal's specific
heat, which you solve for. (The initial temperature of the metal is 100C, since it was hanging in
boiling water. The specific heat of water is 1.0 cal/g·C, from the definition of the calorie, or if you
prefer joules, 4186 J/kg·C.)
Conclusion: Compare your experimental value to the accepted one in the text or formula sheet. Do
they agree within a total uncertainty of 15%?
Part 2: Heat of Vaporization.
You will measure the heat of vaporization of water. The mass of a cup of water is measured. The
container of boiling water is corked, making steam flow through the hose on it. A water trap on the
hose ensures that only steam gets through. This bubbles through the cup of water, where it
condenses. Massing the cup again and subtracting tells how much steam condensed. The
temperature change is also measured. The heat of vaporization is calculated from the idea that the
heat gained by the cool water equals the (negative) heat lost by what was added to it.
Caution: If the hose gets blocked, boiling water could splatter when
the steam generator’s cork pops. To avoid burns, don’t pinch the hose.
Don’t submerge the water trap in the cup, which might make the
steam in it collapse into water, sucking in water which then can’t flow
back out fast enough.
You can use the same cup of water from part one. Measure its
temperature. Put the glass water trap on the end of the hose from the
steam generator. Cork the steam generator so that steam jets from the
tube. (Tongs and gloves are available.) Put the end of the tube in the
cup, with the trap above the water. When not using the steam, leave
the tube's end in a beaker so it doesn't mess up the table.
Stir the water with the thermometer so it isn't in a hot or cold spot. When the temperature has
increased 35 or 40, remove the delivery tube, note the final temperature, and
measure the mass again to determine the mass of the steam added.
Ways it can go wrong:
- If water which condensed elsewhere gets past the trap, it makes msteam too
large.
- If heat is added to the cup without the water it came from getting in the cup,
msteam will be too small. This happens if the water trap is too low, so heat flows through its
walls into the cup of water.
Calculations: The only unknown in ΣQ = 0 will be the heat of vaporization, which you solve for.
Conclusion: Compare your experimental value to the accepted one in the text or formula sheet. Do
they agree within a total uncertainty of 15%?
Part 3: Coefficient of Linear Expansion.
You will measure the coefficient of linear expansion for a metal rod. The rod is inside a pipe with a
cork in each end, the ends of the rod protruding through holes in the corks. To measure how much
the rod's length changes when steam blows through, the apparatus has a built in micrometer at one
end. To show when the micrometer screw touches the rod, a circuit is completed through the rod
making a light come on. From this ΔL, the overall length of the rod, and the temperature change,
the expansion coefficient is calculated, and compared to the book value.
1. Check that the ends of the rod look clean enough for good electrical contact, not rusty.
2. Attach the hose from the steam generator to the nozzle on the steam jacket which points upward.
The hose from the downward pointing nozzle should lead to a large beaker. Leave the cap off the
steam generator for now.
3. Record the rod's length to the nearest millimeter. You may find it easier to measure an identical
rod which is out of the steam jacket; one is available. Check that the screws at each end of the
apparatus line up with the rod, somewhere fairly near the rod's center. (They often get bumped in
storage.)
4. Zero the micrometer. (It's
there to tell you how much the
rod grew, which is presently
zero.):
a. Back off the screw on the
other end.
b. Turn the micrometer dial
until it reads 0.00 mm. The first digit comes from which mark on the little metal bar lines up
with the dial. The last two digits come from which mark on the dial lines up with the little metal
bar.
c. Run the screw on the other end back in just enough to make the light come on.
d. Double check: Back off the micrometer, then run it back in to see if the light comes on at
exactly zero. (To take a reading, run the screw in until the light comes on, and then slowly back
it off until the point where the light just barely stays on.)
5. Back the dial off a couple of turns to allow the rod room to grow.
6. Record the initial temperature of the rod, room temperature, from your thermometer.
7. Cap the steam generator so that steam flows through the apparatus.
8. Wait a few minutes until steam is coming from the drain hose. Turn the micrometer until the
light comes on. Since the rod is now longer, and its other end couldn't move, the screw won't go
back as far as it was before. Record ΔL. (It reads in millimeters.)
9. Turn off the steam. Back off the dial 3 or 4 mm so the light can’t come on and kill the battery.
Tip the apparatus to drain it. Pull out the center cork so the inside dries while in storage. Leave the
drain beaker on the table, not the floor.
Calculations: From the data you have taken, find the coefficient of linear expansion.
Conclusion: Compare this to the accepted value given in the text. Do they agree within a total
experimental uncertainly of 15%?
Again, be sure to look at lab 13 now also. At the start of the period, you will need:
1. The car’s weight (printed on the registration).
2. Its gas mileage.
3. The results of the road test.
PHY 121
Report on Experiment 12: Heat & Temperature
Part 1:
kind of metal _____________________ , mmetal ____________________
mcups _____________________ , mcups&cw ___________________ , mcw ____________________
Initial: Tmetal ____________________, Tcw ____________________
Tfinal ____________________
Calculate Specific Heat:
Part 2:
Before: mcups&water _______________ , mcw _______________, Tcw _______________
After: mcups&water _______________ , msteam _______________, Tfinal _______________
Calculate Heat of Vaporization:
Part 3:
Type of metal ____________________________
Initial length _______________
Initial temperature _______________
ΔL = _______________
Calculation of coefficient of linear expansion:
Book value =_______________