PHYS 1401 – General Physics I
Transport of Heat
Leader: _________________________ Recorder: __________________________
Skeptic: _________________________ Encourager: ________________________
Materials
Cylindrical Ice Blocks
Erlenmeyer flask with stopper
Piece of tubing
Hot Plate
Three Styrofoam Cups
Stop Watch
Digital Caliper
Laptop
Labpro
2 x Stainless steel thermometer probes
Shiny and black can with lids
High Intensity lamp
Safety
1. The hot plates available at the NRG physics lab are very high power. Make sure that you operate them with the wire mesh over the burner and that you treat them as very hot and dangerous.
2. You will be using an Erlenmeyer flask to generate steam. Don’t let all of the water boil out of the flask. This can cause the flask to break. If you are running out of water in the flask, turn off the hot plate, record the time and stop data collection.
3. Do not handle the flask while hot and avoid being scalded by steam.
4. Keep the laptop and LabPro as far as possible from the water.
Introduction
In this activity we will investigate two of the three heat transport mechanisms, namely conduction and radiation. First, we will create a temperature difference across a material of known effective area and thickness and determine the thermal conductivity for that material. We will then examine the rates of heating and cooling for a shiny and black object both illuminated by an intense light source.
Part
1 Thermal
Conduction
Procedure
1. Setup and Preliminary Measurements
Place the
The idea of this lab is that we will add heat to the ice by generating steam. The heat from the condensing steam will be transferred to the ice by conduction through a solid. We will then collect the melted water.
Place one of the Styrofoam cups underneath the trough. This cup will collect the melted ice. Place the second Styrofoam cup underneath the lower tube on the side of the apparatus. This will collect the condensed steam from the apparatus. Measure and record the mass of the Styrofoam cup underneath the trough.
Mass of cup collecting melted ice = ___________________
Use the digital calipers to determine and record the radius of the cylinder of ice.
Radius of ice cylinder = __________________
What is the material through which the heat will be conducted? Note the material may have aluminum covers. You need to look at the edge of the material to see what it is.
Material = _____________
Use the digital calipers to measure and record the thickness of the material through which the heat will be conducted.
Thickness of material = ___________________
Q1) At what temperature does the ice melt?
Q2) How much energy is required per kilogram to melt the ice?
Q3) Will the ice melt even if we don’t generate steam? Explain.
Q4) If the ice melts even if there is no steam, will we tend to overestimate or underestimate the energy transferred through the material from the ice to the steam? Explain.
To avoid this we will first make a measurement of the rate at which the ice is melted by the ambient environment. Remove the cylinder of ice from its form and place it on the face of the apparatus. The two aluminum pieces will hold it in place. Start the stop watch and allow the ambient environment to melt the ice for 10 minutes. While waiting, proceed with part 2 of the lab. After 10 minutes determine the mass of the water collected in the cup. Place a different cup underneath the trough to avoid spilling water onto the table while determining the mass of the collected water.
Water + cup = _________________
Collected Water = ______________
Q5) How much energy was required to melt the amount of ice into water that you collected?
Q6) Remember that power = energy/time. What was the power input into the ice from the ambient environment?
Empty the water from the cup. Turn on the burner and once you are generating steam, place the collecting cup back under the trough. Collect water for 10 minutes again. Turn off the hotplate at this point. Determine the mass of the water collected in the cup. Place a different cup underneath the trough to avoid spilling water onto the table while determining the mass of the collected water.
Water + cup = _________________
Collected Water = ______________
Q7) Does the water you collected this time represent only the melting do to the steam?
Q8) How much energy was required to melt the amount of ice into water that you collected?
Q9) Remember that power = energy/time. What was the power input into the ice in this case?
Q10) How can you find the power that was added to the ice from the steam only?
Q11) Record the power delivered to the ice by the steam.
The power of heat conducted through
a material depends on several factors as given by the expression 
(equation 1). In the expression, ΔQ/Δt is the power of heat added, A is the
cross-sectional area through which the heat flows, l is the thickness of the
material and k is a constant that depends on the material called the thermal
conductivity.
Q12) What is the temperature difference between the two sides of the material? Explain.
Q13) The temperature difference per thickness of the material is called the temperature gradient, ΔT/l. Determine the temperature gradient for this case.
Q14) What is the relevant cross-sectional area through which the heat flowed? Explain.
Q15) Determine the area.
Q16) Solve equation 1 to obtain an expression for the thermal conductivity.
Q17) Determine the value of the thermal conductivity for the material used here.
Part 2 - Radiation
In this lab, we will explore how the temperature of objects that absorb light differently change temperature when they are illuminated by a strong light source.
Procedure
1. Set Up
Place the lid on the can and insert the temperature probes through the hole on the lids into the can. Connect the probe in the black can to CH 1 on the LabPro and the probe in the silver can to CH 2. Start LoggerPro. The program should automatically detect the two temperature probes. If it doesn’t, contact your instructor. Click on the Experiment menu and then click on Sampling … Adjust the data collection time to 15 minutes.
2. Data Collection
Plug in and turn on the lamp. Arrange the lamp and the cans so that the lamp is about 6” from the cans, and illuminates the cans evenly. The cans should not touch. Click on the collect button. After 7.5 minutes, turn off the lamp while still collecting data. Do not stop data collection when you turn off the lamp. Continue until the data collection ends.
Data Analysis
Examine your graphs.
Q18) Which of the cans seemed to go up the fastest in temperature?
Q19) Which of the cans seemed to go up slowest in temperature?
Q20) Which of the cans seemed to go down the fastest in temperature once you turned the light off?
Q21) Which of the cans seemed to go down slowest in temperature once you turned the light off?
Q22) If an object rises in temperature rapidly, it will go down in temperature ________.
Q23) If an object rises in temperature slowly, it will go down in temperature ________.
Important
Information
Emissivity is a measure of how effective an object is at absorbing and emitting radiation. Emissivity is a number without units which ranges from 0 to 1. Something that readily absorbs and emits radiation will have an emmissivity close to 1, whereas something which is a poor absorber and emitter of radiation will have an emissivity closer to 0.
Q24) Which has a higher emissivity, the black can or the silver one? Explain.
Q25) If you wished to prevent heat transfer by radiation, should you use an object with a high or a low emissivity? Explain.