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A positively charged rod is used to charge a sphere by induction. Which of the following is true?
  1. The sphere must be a conductor.
  2. The sphere must be an insulator.
  3. The sphere can be a conductor or insulator but must be connected to ground.
  4. The sphere can be a conductor or insulator but must be already charged.
Question by OpenStax is licensed under CC BY 4.0.
Solution Video

OpenStax College Physics for AP® Courses Solution, Chapter 18, Problem 18 (Test Prep for AP® Courses) (1:08)

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This is College Physics Answers with Shaun Dychko. A positively charged rod is used to charge a sphere by induction and which of the following is true? And the answer to that question is (a) and I'll show you why. Suppose you have a positively charged rod and you bring it close to an initially neutral sphere... charging by induction means that there's going to be a charge distribution created by this charged object being close but not quite touching the object and so we are going to have electrons on the near side of this sphere and then it's going to leave behind some atoms that will become positively charged since they are missing these electrons that went to the near side. Now in order for these electrons to move, this object has to be a conductor otherwise you know that's the definition of what a conductor is is that there are free charges capable of moving and so an insulator wouldn't do this and so the answer has to be (a).