Investigation 17C: Resistors and Ohm’s law

Essential questionsHow is resistance measured?
Ohm’s law, I = V/R, is the fundamental relationship among current, voltage, and resistance in a circuit. Devices that measure resistance are based on Ohm’s law. These devices apply a known voltage and/or current, then determine the resistance. In this investigation you will use a similar experimental technique to measure the resistance of a bulb.
Part 1: Current through different resistors

Part 1: Current through different resistors
  1. Open the experiment file 17C_ResistanceAndOhmsLaw, and then power-on the current sensor and connect it to your software.
  2. Construct the circuit shown using one battery, a switch, a current sensor, a 10-Ω resistor, and any necessary wire modules.
  3. Start data collection, close the switch, and record the measured current in the data table.
  4. Repeat the experiment for the 33-Ω and 100-Ω resistors. Tabulate your results for R and I.
  1. Graph I on the vertical axis and R on the horizontal axis. What type of curve best fits this data?
  2. Calculate 1/R for each resistor. Make a second graph with I on the vertical axis and 1/R on the horizontal axis to create a linear graph. Fit a line to determine the slope of the data. What is the value of the slope?
  3. What does the slope of this graph represent? Why?
Part 2: Resistance of a light bulb

Part 2: Resistance of a light bulb
  1. Power-on the voltage sensor and connect it to your software.
  2. Replace the resistor with the bulb and attach the voltage sensor across the bulb.
  3. Measure the current and voltage for the illuminated bulb.
  4. Calculate the resistance of the bulb using Ohm's law, R = V/I.
  1. What is the resistance of the bulb? Show your work, including units.
  2. Imagine you have a complicated circuit containing many resistors. Describe in words how you can use Ohm's law to find the effective resistance of the entire circuit.

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