Physics 115B
Lab 1: Energy, Temperature, Heat, and Power
Learning goals
• “Technique”: looking for lab practices that make a
measurement reliable.
• Distinguish between heat and temperature.
• Measure energy in different forms and demonstrate that it is
conserved.
• Apply these experiences to everyday life.
Part I: One Temperature - Many Thermometers (45-60min)
There is a collection of thermometers on the tables, including
an unusual Star-Trekky one (the “grey instrument”, “g.i.”) and
several digital thermometers, some hooked up to computers.
1. Using the "contact" thermometers (the ones that need to touch
whatever they are measuring), take about 10 minutes to measure
and record the temperature of a few objects (your fingers,
computer, etc.). Does it matter how it's done? What do you
observe about the temperature readings over time (stable, slowly
changing, etc.)?
2. Now, study and play with the "non-contact" g.i., Take about 10
minutes to use it on yourself (or a partner), on the wall, on a
computer screen, and at least four other interesting items. Make
a table in your notebook showing the results. Again, does it
matter how it's done?
3. There is a red lamp on a nearby lab table. Some of the light
shines on a few mirror-like surfaces. Use the g.i. to measure the
bulb temperature. Now use it to measure the temperature of the
reflection of the bulb in the mirror. Is the mirror really that hot?
Discuss how the g.i. may work in this case and put some
speculations in your notebook. Describe in one paragraph
some real-world situations where the g.i. could be useful and
when it may be inaccurate.
4. Fill a glass beaker with tap water and use the computer
thermometer on the water. Once you have the baseline
temperature, gently stir the water with the thermometer. Does
the temperature change? Is the energy of the water changing?
Discuss in notebook your thoughts about why it does or does
not.
5. Put your hands around the beaker and repeat Step 4 with the
computer thermometer. Discuss the same issues in notebook.
Part II: Liquid Nitrogen Demos (5-10 min)
Physical properties can change dramatically with temperature.
The AI’s will show you cool things with serious cold!!
Part III: Transforming Kinetic Energy to Heat Energy (2030 min)
1. Carefully open the bottle and see what is inside. Measure the
temperature in the middle of the copper shot using a computer
thermometer. Make sure the thermometer doesn’t touch the
bottom of the plastic bottle. Leave the thermometer in place
and let the temperature “stabilize”. If it is slowly drifting, just
record the approximate temperature.
2. Describe (to your lab partners and in your notebook) what
would happen if you shook the bottle vigorously and then set it
down. We want a description in terms of energy. (e.g. Energy
in what form? From where?) Would the energy content of the
bottle change? What about the temperature? What if you
waited awhile afterward?
3. Put the lid on the bottle and shake it 40 times vigorously then
repeat your temperature measurement. Watch it for a while.
Record what you observe, then sketch the how the
temperature varies with time. Compare what you observe to
your expectation in Step 2. Try repeating the experiment
several times. (Everyone should do it at least once.) Why
might such repetition be useful? Describe several reasons.
4. Discuss briefly in notebook the similarities and differences
from your predictions. Speculate why you may be seeing the
differences (if any).
Part IV: Heat and Temperature (30-45 min)
Using the materials available on the table, we’ll take a look at
how objects can store heat. In order to see this accurately, you’ll
need to make some careful measurements and record the data in
your notebook. You will follow the steps listed below. Read the
steps now, but, before you do them, read the rest of this section.
You should understand exactly how the steps will allow you to
determine the specific heat of your sample before you start making
the measurements.
1. Get a metal block (Aluminum) from an AI and measure its mass
(Mmetal). Also measure the mass of an empty styrofoam cup.
2. Fill a glass beaker with cold water and ice (see AI). You’ll find
the ice in the freezer and cold water in the refrigerator.
3. Put room temp tap water in a styrofoam cup - there should be
just enough water in the cup just to have your block completely
submerged. Measure total mass of water in cup. From that
determine the mass of the water (MH20). Measure its temperature
without the block (TH20,intial). You can use two probes on the
same computer, one for the ice water, one for the tap water.
4. A string is attached to the metal sample. Use it to place the
metal it in the ice water. Leave for 1 minute. Measure the
temperature of the ice water (Tice water =Tmetal,initial). Make sure
thermometer isn’t touching an ice cube.
5. Then, carefully remove metal from ice water and place in the
styrofoam cup of water. Stir with thermometer and track the
temperature on the computer. When it reaches a nearly
constant value, record it: (TH20,final=Tmetal,final).
We can connect the temperature change of the water to energy.
Recall from the lecture that the heat (energy) required to raise the
temperature of 1 kg of water by 1°C is 1 Calorie ≈ 4200 J, so it
takes about 4.2 J to raise 1 g of water by 1°C.
Consider the following:
• How much did the temperature of the water in the
styrofoam cup change when the block was added?
• How many Joules of heat energy did the water lose?
• What principle allows you to determine the change in the
energy of the block?
• By how much did the block’s energy change?
• Did the block’s temperature change by the same amount
as the water?
Recall that temperature and heat are related, but not the same!
Each substance has a “specific heat,” the amount of energy needed
to raise 1 g of the substance by 1°C. From the above discussion,
the specific heat of water is CH2O ≈ 4.2 J/g-°C. (It can also be
quoted in other units, for example, 1 Cal/kg-°C). In this lab, C
does not depend on the mass, shape, or temperature of the material
– it just depends on what the object is made of.
Use this definition and your measurements to figure out the
specific heat, Cmetal, for your block. Report your result to one
of the AI’s. Does your metal or water have the higher specific
heat?
Discuss and list some real-world situations when having a
material with high specific heat or low specific heat can be
important. REMEMBER: high specific heat is not the same as
high thermal conductivity!
Part V: Electrical Energy and Power – a Watt is a Watt
(20-30 min)
The 100-Watt light bulb has been set up for safe immersion in
water. (Don’t try this at home!)
1. Locate the setup with an orange water jug, light bulb & stand,
and the Kill-A-Watt meter. Male sure the bulb is outside of the
jug for now and make sure bulb is dried off (paper towels near
sink). Try plugging the light into the Kill-A-Watt meter and the
meter into the wall. Try the various buttons. How much
electrical power is being used? Now, we will try to measure
this ourselves.
2. Unplug the meter from the wall so the light is off. Place the
light bulb stand so the bulb is in the jug close to the bottom then
add 1000 ml of water. Figure out the mass of the water. (Why
is this easy?) Put the probe of a digital thermometer in the
water. It should not touch the wall of the jug or the bulb.
Measure the temperature of the water with the bulb off.
3. Turn on the bulb. Use a plastic ruler to stir the water gently and
continuously so water circulates around bulb. Record the
temperature of the water over time with the computer probe for
several minutes. Print a plot of the temperature vs. time and
place in your logbook.
4. We can connect the temperature change of the water to energy.
Recall from your textbook that the heat (energy) required to
raise the temperature of 1 kg of water by 1°C is 1 Calorie ≈
4200 J, so it takes about 4.2 J to raise 1 g of water by 1°C. At
what rate is energy being added to the water (J/s = Watts)
while the bulb is on? Should it be 100 W? Why or why not?
Is there a limit to the process?