Preliminary Thoughts and Questions
Initially, effects associated with temperature were believed to be unrelated to work and mechanical energy. Thermal effects were associated with the transfer of something called "caloric" (hence the unit calorie) which was contained in the material. The transfer process of the caloric from one object to another was call heat. The caloric was conserved just as mass and mechanical energy were conserved, but each object had a finite supply of caloric.
While supervising the boring of cannons, Benjamin Thompson (Count Rumford) noticed the work of boring produced hot metal including chips. The chips were able to boil water even if very small. This suggested that the "caloric" content of a material was not limited.
Others studied the phenomenon, but it was James Prescott Joule who first quantified the effect. Joule did a known amount of work to turn a paddle in an insulated container of water. He found that the ratio of work to heat was always the same (the ratio is called the mechanical equivalence of heat). This showed work and heat were part of the same general category of energy, but with different units and that 4.186 Joules = 1.000 calorie (now defined to be exact).Thus, the caloric theory was inconsistent with measurement and dropped. And, a new form of energy - thermal energy - was introduced for energy conservation.
Similarly, there is work associated with electrical circuits and current flow. This electrical work will also produce thermal energy, e. g., an electric stove. This is what you will investigate.
To calculate the electrical work, we need to
review electrical units. The unit of charge is a coulomb, C, in the
SI system. "Voltage", V, measures the energy per charge in a circuit.
The units are Volts in the SI system: 
Current measures the charge flowing past a region every unit of time.
The units of current, I, are Amperes in the SI system: 
.
The voltage across a region times the current through the region
equals the electrical power (work per time), P = V I. To find the
electrical work, we must multiply the power by the time interval (the
amount of time V and I are present. Electrical work is 
.
If electric work is similar to mechanical work, then electrical work and energy should be a term in energy conservation. Assuming all the electrical work is converted to thermal energy, how should the totals compare?
One Food Calorie (capital "C") equals 1 kilocalorie. How many joules is one food Calorie?
Apparatus voltmeter, ammeter, power supply, stop watch, Pasco Electrical Equivalent Heat (EEH) jar, black India ink, scale, thermometer, water, paper towels
Procedure:
Wire the circuit shown in the diagram below. For best results, connect the voltmeter leads directly to the binding posts of the jar. The voltmeter measures the voltage between the two leads. The ammeter measures current flowing through the leads. The meters will measure the voltage and current for the light bulb. Assume all of the energy exchange is between the bulb and water only.
Fill the jar to the indicated water line with cold water. DO NOT OVERFILL. If possible, the water should be approximately 5šC below room temperature.
Add about 10 drops of India ink to the water, enough so the lamp filament is just barely visible when the lamp is illuminated.
Only turn on the power supply when the light bulb is in the water. Turn on the power supply and quickly adjust the power supply voltage to about 11.5 volts, then shut the power off. DO NOT LET THE VOLTAGE EXCEED 13 VOLTS.
Stir the water gently with the thermometer or probe while observing the temperature.
When the temperature warms to about 5šc degrees below room temperature, simultaneously turn power supply on and start you timer (so t ¡= 0 in table).
NOTE: You may want to turn the lamp on to help the cold water reach this starting temperature. If you do, be sure that you turn the lamp off for several minutes before you begin your measurements, so you are sure the water temperature is even throughout the jar. Record the starting time (t¡) and the temperature (T¡).
Record the current, I, and voltage, V. Keep an eye on the ammeter and voltmeter throughout the experiment to be sure these values do not shift significantly. If they do shift, use an average value for V and I in your calculations.
When the temperature is about 5šc above room, shut off the power and record the time and Continue stirring the water gently. Watch the thermometer or probe until the temperature peaks and starts to drop. Record this peak temperature.
Analysis:
Calculate the Electrical Equivalence of Heat = E/Q.
Questions:
1. Explain how your experimental value for the Electrical Equivalence of Heat would change (lower or higher or no change) if the inked water is not completely opaque to visible light?
2. Explain how your experimental value for the Electrical Equivalence of Heat would change (lower or higher or no change) if there is some transfer of thermal energy between the calorimeter and the room atmosphere. (Hint: Why did you start below room temperature?)
3. Explain how your experimental value for the Electrical Equivalence of Heat would change (lower or higher or no change) if the thermometer and the bulb inside the calorimeter were also heated.
4. How does you measured Electrical Equivalence of Heat compare with the Mechanical Equivalence of Heat and how should they compare?
5. A typical food diet requires a person to consume 2000 Calories a day. How many Joules are consumed in a day?
6. A can of Diet Coke from Australia says it contains 0.9 kJoules. How many calories does it contain? How many food calories?