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Lesson: Design of the Ohmmeter Physics

In this lesson, we will learn how to describe the combining of a galvanometer with fixed and variable resistors to design a dc ohmmeter.

Lesson Plan

Students will be able to

  • describe the appropriate connection of a galvanometer and fixed and variable resistors to produce an ohmmeter,
  • explain the required resistance ratio of the fixed and variable resistors,
  • explain the nonlinear variation of the arm deflection of an ohmmeter with linear change in measured resistance.

Lesson Presentation

Lesson Video

Video Thumbnail
13:12

Lesson Explainer

Lesson Playlist

Lesson Worksheet

Q1:

A circuit that can be used as an ohmmeter is shown. The circuit uses a galvanometer, a direct-current source with a known voltage, a fixed resistor, and a variable resistor. Which of the following most correctly states how to calibrate the circuit to directly measure the circuit’s total resistance?

Q2:

The diagram shows the scale of an ohmmeter that is being used to measure an unknown resistance. The resistance of the ohmmeter is 25 kΩ. The angle of full-scale deflection of the ohmmeter Φ=60∘. The angle of deflection of the ohmmeter arm 𝜃=30∘. What is the unknown resistance? Answer to the nearest kilohm.

Q3:

The diagram shows the scale of an ohmmeter that is being used to measure an unknown resistance. The resistance of the ohmmeter is 25 kΩ. The angle of full-scale deflection of the ohmmeter 𝜙=60∘. The angle of deflection of the ohmmeter arm 𝜃=48∘. What is the unknown resistance? Answer to the nearest kilohm.

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