This problem requires two resistors.  Use four 1/4 watt resistors.  You will have two resistors of one value, R_a, and two resistors of another value, R_b.

• You will need a power supply that can produce a variable voltage - up to 25 or 30v.
• As questions are raised in this lesson, you should record your answers and any supporting experimental observations in your laboratory notebook.  You will need that data and those thoughts to write your report.
• Your analytical/paper work should be done and handed to your instructor before you begin the experimental work.
• Your analytical work should be done entirely symbolically.  You will not learn values for the bulbs until you have done the theoretical work.

• Imagine applying a voltage, V1 to two resistors in parallel.  Assume both resistors have the same wattage rating.
• Predict which resistor will get warmer, and record your reasoning in your lab notebook.
• Imagine applying a voltage, V2 to two resistors in series.  Assume both resistors have the same wattage rating.
• Predict which resistor will get warmer, and record your reasoning in your lab notebook.
• Now, hand in your work to your instructor and begin the experimental portion of this exercise.

• Apply 5v to a 100W resistor in parallel with a 150W.  Wait for the two resistors to come to thermal equilibrium.  Wait at least two minutes.
• Do not touch the resistors during this period.  Then, see if you can determine which resistor is warmer.  (You can use a thermocouple to measure temperature?)
• Determine if the resistors are operating within their rated range.
• Now, slowly increase the voltage above 5v.  At this point you are putting a voltage across the resistors which will eventually take them beyond their rated wattage.  As you carefully and slowly increase the voltage, the resistor which first emits smoke is the one which is warmest.  Turn off the power supply, and let that resistor cool down to room temperature and measure the resistance value to determine if it has changed value.

• Apply 12v to a 100W resistor in series with a 150W.  Wait for the two resistors to come to thermal equilibrium.  Wait at least two minutes.  Do not touch the resistors during this period.  Then, experimentally determine which resistor is warmer.
• Determine if the resistors are operating within their rated range.
• Now, slowly increase the voltage above 12v.  At this point you are putting a voltage across the resistors which will eventually take them beyond their rated wattage. As you carefully and slowly increase the voltage, the resistor which first emits smoke is the one which is warmest.
• Turn off the power supply, and let that resistor cool down to room temperature and measure the resistance value to determine if it has changed value.