Name: _____________________ Class: Physics 214
SSN/ID:   _____________________ Section & Group: ____________
Lab 3 - Temperature and Heat

Objective
To determine the temperature of a liquid in degrees Fahrenheit and Centigrade and to use the data to confirm the general relationship between the two scales. Also, to determine the specific heat of a metal object by measuring the amount of heat transferred from that metal object to another, cooler body (of water). But the main purpose of this lab is to elucidate the scientific method at work. The idea is to make a guess (your hypothesis) based on some underlying reasoning. Then, you perform an experiment to confirm or deny that hypothesis and, based on the results, modify your guess (your hypothesis), if necessary.

Equipment
See the Shockwave applets below. All data and calculations can be recorded using these sheets and your handout.

Definition
The main idea in this lab is to make a guess, or hypothesis, for how long you think it'll take water to boil. What differentiates Science from things like Astrology is the precision and testability of our predictions. Both Astrologers and Physicists make predictions; the only difference is that the Physicists' predictions are exact and subject to objective verification.

You can make a theoretical prediction (or hypothesis) based on your theory (as opposed to an intuitive prediction based on no pre-knowledge and just whatever patterns you pick up on). You have learned enough science in this class to predict how much heat will be needed to raise the temperature of a certain mass of water from a certain temperature to boiling. The idea is to use this required amount of heat energy, and the rate at which heat energy is being pumped in, to predict how much time that process should take.

In order to get water to boil, you have to raise its temperature to 100oC (at a pressure of 1 atmosphere). If you know the amount of water you have, and the temperature it starts out at (room temperature = 20oC), then you can determine just how much heat energy that mass of water will need to get to boiling temperature. If you also know the power, or the heating rate (remember, power is given in units of [Watts] = [Joules/second]), you can determine just how long it'll take to transfer the amount of heat you need to make the water boil. This can be done by dividing the amount of heat energy needed by the power, or heating rate, (which is simply the amount_of_energy_transferred / time). This is symbolized as:


                  [amount_of_heat_needed]     [amount_of_heat_needed]
[time_required] = ----------------------- = ---------------------------
                          [power]           [energy_transferred]/[time]

Procedure

Is there anything more exciting than watching water boil?

  1. Set the initial water amount
  2. Set the starting water temperature
  3. Set the heating power
  4. Finally, enter how long you think it will take to boil the water (this is your guess or hypothesis)
    • Please note, the boiling point of water is 100oC
    • Compute the amount of heat energy needed to boil your sample of water using the following formula: Q = m c ΔT
    • Use the amount of energy (computed above) and the heating power to calculate how long it should take the water to boil (this time will be your hypothesis/guess):
                             Energy Transferred    [Joules]    Heat Energy   [calories]    Q     
      Heating Rate = Power = ------------------ = ---------- = ----------- = ---------- = --- 
      	                     time             [sec]         time         [sec]       t  
      
      	     Q     m c ΔT
      ==> Power = --- = --------
      	     t       t
      
      	    m c ΔT
      ==> t = ----------------
      	 (Heating Rate)
      	
      Please remember that Power (the heating rate) is just Energy/Time (either Joules/sec or calories/sec).

      STOP! Record how you obtained your hypothesis on the fill-in sheet or handout and show them to your class supervisor before you proceed...

  5. Now Start the experiment; when it finishes, note the actual time it took to boil and also how accurate your guess was (the accuracy is displayed as a percentage of the actual time)
  6. Now repeat Steps 1-5, holding the water amount and starting water temperature constant (keep them the same)
    • However, change the heating power to be greater than your original value
  7. Now repeat Steps 1-5, holding the heating power and starting water temperature constant (keep them the same)
    • However, change the water amount to be greater than your original value this time around
  8. Did your hypothesis improve with Runs 2 and/or 3?

Run Water Amount
[kg]
Starting Temp
[oC]
Heating Power
[J/sec]
Heat Energy Needed, Q
[J]
TimeHypothesis
[sec]
TimeActual
[sec]
Accuracy
[%]
1.                
2.                
3.                

The Shockwave Applet:

URL: http://ippex.pppl.gov/interactive/energy/boil_water.dcr



Questions

  1. In an actual experiment (as opposed to this idealized experiment), what other factors might affect the boiling time? For each factor you identify, would it increase or decrease the time?

Notes