Investigation 17E: Electrical power

Essential questionsHow is power related to energy?
What determines the power rating of a device?
Electrical devices are commonly rated in units of power, such as a 100-W light bulb or a 1200-W microwave. The electric company bills homes in units of energy. Why the difference? In this investigation, you will build circuits containing two different resistors in series and parallel (representing two different electrical devices) and measure the power and energy output of each device for each circuit.
Part 1: Resistors in series

Part 1: Resistors in series
  1. Open the experiment file 17E_ElectricalPower and then power-on the Current and Voltage sensors and connect them to your software.
  2. Construct the circuit shown. Connect the voltage sensor across the 33-Ω resistor.
  3. Begin recording data and close the switch. Continue recording data until the energy has reached 1 joule.
  4. Repeat the experiment for the 100-Ω resistor.
  1. What happens to the power output for each resistor when the switch is closed? The energy measurement?
  2. Which resistor recorded a higher power output? Why?
  3. Which resistor consumed 1 joule of energy the fastest? How is this related to the power output?
  4. Fit a line to each energy versus time run. How does the value of the slope compare to the power output? What does the slope represent?
Part 2: Resistors in parallel

Part 2: Resistors in parallel
  1. Construct a circuit using the same components as Part 1, but wire the resistors in parallel. Place the current sensor in series with the 33-Ω resistor and connect the voltage sensor across the 33-Ω resistor.
  2. Begin recording data and close the switch. Continue recording data until the energy has reached 1 joule.
  3. Repeat the experiment for the 100-Ω resistor.
  1. Does each resistor have the same power output as Part 1? Why or why not?
  2. Which resistor has the higher power output? Is this the same as the results in Part 1? Why or why not?
  3. Do the resistors consume energy faster in series or in parallel? Why?
  4. Does the power output of a device depend on the properties of the device, how it is wired in the circuit, or both? Explain.

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