Experiment 14 Heat & Thermo Lab1

Temperature

The coffee and the bath water are at the same temperature.  Both are ÒhotterÓ than the air in the room.  However, it costs much less to heat the coffee than it does to heat the bath water. Why?  ArenÕt the words heat and temperature synonymous?  Is heat a substance or what?  In this unit you will learn how contemporary physicists define and use familiar terms like ÒheatÓ and ÒtemperatureÓ to help them understand thermal processes.

 

. . . . thermometer readings alone do not tell the entire story of thermal interactions, . . . something else must  be happening, and . . . an additional concept (or concepts) must be invented.

A. Arons

 

Lab GroupNames

Author:     ________________________

Technician:________________________

Analyst:    ________________________

Date:                  ________________________

Part I.  Temperature Scales

Suggested Reading:  201- 10-1 thru 10-3

                                    213 - 19-1 thru 19-4

Objective 1.  The object of this part is to convince us that the relationship between any two temperature scales ia a linear function.  In other words, if an object has temperature TA using scale A, and temperature TB using scale B, then TB = (some constant)*TA + (some other constant), or, for the severely mathematically  impaired, TB = (slope)*TA + TBintercept.

To accomplish this formidable task we will invent our own temperature scales and take the temperature of 8 different things with our thermometer, as well as with both Centigrade and  Fahrenheit thermometers.  Then we will graph Tours vs TC, Tours vs TF, and TC vs TF.

 

 To conduct this investigation and several others in this session you will need:

¥ An unmarked glass bulb thermometer (Blue capped tube), cab 4D

¥ Masking tape for marking temperature scales, See Instructor

¥ A Centigrade glass bulb thermometer (Yellow Tube) Cab 4D

¥ Boiling Tap water, on Table 1

¥ Boiling Alcohol, on Table 1

¥  Boiling Salt Water, on Table 1

¥ Room Temperature Tap water, on Table 1

¥  Body Temperature, Yours

¥ Salt(NaCl)water on ice, on Table 1

¥ Ice Alcohol, Table 1

¥ Ice Tap Water, on Table 1

¥ Styrofoam cups w/ insulating lids, cab 4C

¥  Graphical Analysis

 

Activity 1.  How to build your own Thermometer

 

a)  First place a 6" piece of Scotch tape lengthwise on an unmarked thermometer as directed by the instructor.  Obtain two easily reproducible Òfixed pointsÓ of temperature from the table below and mark these on the tape.

 

b)  Decide what number to assign to either the top or bottom fixed point temperature and label it .

 

c)  Decide how many units (ÒdegreeÓ marks) you want between the two fixed points, mark and label the other end point and at least 5 points between the two.

 

  Creating your own thermometer.

 

Choose your 2 fixed points from the following available items, and follow steps a, b, & c above to create your own thermometer.

 

Boiling water

boiling alcohol

boiling salt water

your own temperature (armpit)

room temperature water

room temperature alcohol

      Ò               Ò      metal

      Ò               Ò      wood

ice water

ice salt water

ice alcohol (cup of alcohol sitting in ice bed)

 

1.  Using thermometers marked with a Fahrenheit , Celsius(centigrade). and our scale, complete the following table.

Item

Fahrenheit (TF)

Celsius (TC)

Your  (Tours)

Boiling Salt Water

 

 

 

Boiling water

 

 

 

body temperature

 

 

 

room temperature

 

 

 

ice alcohol

 

 

 

ice water

 

 

 

ice salt water

 

 

 

 

2.  Use Graphical Analysis to plot a graph of TC vs Tours.  If the curve looks like a line, use automatic curve fit and click the appropriate dot  to obtain the equation of TC as a function  of  Tours.

Obtain a printout of your graph and include it when you hand in this activity.  Be sure it is labeled clearly.

 

Write your equation here:  TC= ______________

 

3.      Repeat for Tours vs TF .  Write our equation for Tours as a function of TF here.  Tours = ________

 

4.  Testing our Accuracy:  Repeat for TC vs TF  Write your equation here:  TC= ______________

 

Note:  your data for TC vs TF should indicate that the relationship between TC & TF is linear, but due to our crude thermometers, your equation may not be exactly right.  Use the fact that water boils at 212o F and 100o C , and freezes at 32o F and 0o C , find the ÒcorrectÓ relationship by determining the equation of the line thru the points (32 o, 0 o), & (212o, 100o).  Comment on your accuracy:

 

Show the algebra you used to obtain the actual formula here.

 

 

 

Objective 2:  Understand how change in temperature affects different materials.

 

The molecules in any solid or liquid are actually vibrating at all times, in gases they actually move.  This gives them a kind of kinetic energy.  Temperature is actually a measure of the average kinetic energy per molecule in a substance.   Bang on a penny with a hammer and it will heat up.  That's because all that banging rattles the molecules in the penny causing the average kinetic energy per molecule to go up.  Since they are vibrating more violently, the penny actually swells up.  Different elements and compounds swell different amounts with the same amount of increased  kinetic energy per molecule.  Thus, different substances have different coefficients of linear expansion.

 

 

 

- Discussion 1: The coefficients of linear, area, and volume expansion.

 

Consult the Temperature Coefficient of Expansion table in your text for values of a

Note the formulas :

 

DL = aLoDT

DA = gAoDT = 2aAoDT

DV = bVoD = 3aVoDT

 

- Discussion 2: The Glass Bulb Thermometer

Sketch a picture of a glass bulb thermometer. Explain how it works.

 

 

Objective 3:  Learn how  to use the electronic  temperature probe.

 

Sensing Temperature Electronically

 

Next you will explore temperature measurement with an electronic temperature sensor that can be attached directly to the microcomputer at your lab station. This system has several advantages over the use of the glass bulb thermometers. The sensors usually respond more quickly to changes in temperature. You can produce a graph of temperature vs. time for one or two sensors at a time automatically. And, as usual, the data you collect can be displayed in tabular form and transferred to other programs for further analysis and display. The purpose of this activity is to become familiar with electronic temperature measurement, some of the limitations of electronic sensing, and features of the temperature measuring software.

 

To carry out these investigations you will need in addition to some of the other materials used earlier in this session:

 

 

                        ¥ LoggerPro Icon  - Under the Apple Menu

                        ¥ a temperature probe G/S -1

                        ¥ a Lab Pro - in red toolbox in PS-5 (under the glass cabinets)

 

To get started:

 

Activity 2:  Introduction to the Temperature Probe.

1.  Plug the temperature probe into the LabPro.

 

2. Find the temperatures of the air around you.  Open Logger Pro.  A temperature-time axis should appear on the screen with the current temperatures being read by  the probe(s) at the bottom of the screen.

 

Electronic vs. Glass Bulb Temperatures

Our new temperature sensors are fairly accurate without calibration, but you may calibrate if desired.

 

Caution!!   Cups will NOT support the thermometers !! Hold onto cup with one hand and thermometer with the other at all times!!

 

Note :  You will have to use a styrofoam lid for the hot water in order to obtain a stable reading (otherwise it cools off too fast), poke the thermometer and probe thru holes in the lid.

 

- Activity 3: Comparing Temperatures

(a)   To determine the accuracy of the temperature probe,  re-measure a couple of temperatures using both kinds of thermometers for a reality check. Try ice alcohol and boiling salt water for a check and fill out the table below.

 

 

Glass Bulb

Therm (o C)

Electronic

Therm (o C)

Difference

(o C)

Ice Alcohol

 

 

 

Boiling Salt Water

 

 

 

 

(b) How close is the electronic reading to your "standard"?

 

Note: If you are off by more than ±1 degree Celsius you should re-calibrate carefully before any session where accurate temperature readings are needed. Don't bother re calibrating now unless you are off by 5¡ or more.

 

Some Important Properties of Temperature Sensing

There are a couple of things you should know about temperature sensing in order to measure temperature more accurately.

 

-      Discussion 3: Time Delays

 

(a) When a nurse pops a room temperature thermometer in your mouth to see if you have a fever, can the temperature be determined immediately? Why not?

 

 

 

 

 

(b) Suppose you want to measure room temperature with a thermometer that has been in ice water. Which do you predict would cause more time delay, measuring room temperature water or room temperature air? Explain the reason for your prediction.

 

 

 

 

Note:  You really should use two temperature probes to do this part and part (e).  You can share with another group, or simply do each part separately.  You'll need to calibrate the new temperature probe.

 

Do!(c) Use the Standard Temp Probe program to verify your prediction quantitatively by recording how the temperature of an electronic temperature sensor changes over time when it is transferred from ice water to room air and vice versa.  (YouÕll need to set the scales to 0 & 25 0 C and 0 to 300 seconds.)

 

                                    Stabilize both thermometers in the ice water, then click on Collect and place one in the room temperature water and wave the other around in the air.  Continue until both stabilize at room temperature.  Click on analyze to obtain the times.

 

Ice water to room air:       Dt (sec) =  

 

Ice water to room temp water:  Dt (sec) =  

 

Discuss! (d) On the basis of these measurements what should you watch out for in making temperature measurements?

 

 

 

 

Discuss! (e) The temperature difference between room temperature and ice water is about 20¡C.  What do you think will happen to the measured time delays if the temperature of the sensor is only a degree or two below room temperature?  Try it!   Make some cool water in a styrofoam cup, and some room temperature  water in another.  Place both sensors in the cool water until they stabilize.  Then place one in the warm water, and wave the other one around in the air.

 

 

                                    cool water to room air:      Dt (sec) =  

 

 

                              cool water to room temp water:  Dt (sec) =

 

Compare and comment on  the ratios  DT/Dt  for these two cases to the ones above in part (c)

Discussion -Can we trust our "feelings" when it comes to temperature ?  Discuss this demo but do not do it. 

 

Thermal Equilibrium

Are objects lying around a room really at the same temperature?  To explore this question of thermal equilibrium you can use the following:

 

¥ A piece of metal with a sensor hole Cab 1-B

                        ¥ A piece of Styrofoam with a sensor hole Cab 4-C

                        ¥ A piece of wood with a sensor hole C4-C

                  ¥ A thermometer or MBL temperature system C4-D 

 

-      Activity 4: Predicting Relative Temperatures

 

(a) Feel the wood, metal, and Styrofoam.  Predict which one  actually has the highest temperature and the lowest temperature.

 

 

 

(b)  Now measure the temperature of the three objects and record your measurements in a table below.

 

 

 

 

(c) Did your observation jive with your prediction? _______  Is your sense of touch an accurate predictor of relative temperatures? __________

 

(d) According to other observations you have made in this session, should the temperatures of three different materials sitting around in the same room be the same or different?

 

 

 

(e)    On the basis of previous observations, you should be able to explain the reason why some objects feel colder than others. Hint: Is the temperature of your hand different

 

than the room temperature? If so, what is happening when you touch an object which is at room temperature?

Problems Assigned:  (In addition to those in Chapter 19 (213) or chapter 11 (201)

 

1.  A 40 Fo  increase in temperature of an object would be what increase in Co ?

 

 

2.  A 60 Co drop in temperature of an object would be what change in temperature on a Fahrenheit scale?

 

 

3.  A change of 80 Kelvins on the absolute temperature scale would be what change on the:  a) Centigrade scale, b) on the Fahrenheit scale?

 

 

4.  At what temperature are the Kelvin and Fahrenheit scales the same?

 

 

 

5.   At what temperature are the Centigrade and Fahrenheit scales the same?

 

6.  At what temperature are the Kelvin and Centigrade scales the same?

 

 

 

7.  The New River Gorge bridge in West Virginia is a steel arch bridge 518 m in length.  How much will its length change between temperature extremes of -20 degrees C and 35 degrees C?

 

 

 

 

8.  If a fast marble hits a random scattering of slow marbles, does the fast marble usually speed up or slow down?  Which gain(s) kinetic energy and which lose(s) kinetic energy?  How do these questions relate to the direction of heat flow?

 

 

 

 

9.  Suppose you apply a flame for a certain amount of time to 1 liter of room temperature water and the temperature rises 2o C.  If you apply the same flame to 2 liters of room temperature water for the same amount of time, by how much will its temperature rise?

 

 

 

10. Approximately what is human body temperature on the Celsius temperature scale?_____

 

 

 

11.       Which is better at transferring heat , water or air?  How does this fact explain the length of time it takes the temperature probe to reach thermal equilibrium with the air or water it is in?