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A radioactive substance A was placed in a lead-lined container and the radiation it emitted was allowed to pass through a small aperture in the container and below a positively charged plate. The path of the particle changed such that it angled up toward the plate. Which of the following could it be?

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Correct Answer: B. Beta particle
Since the radioactive emission angled up toward the positive plate, it must be oppositely charged, that is, negatively charged. The only negatively charged species in the answer choices is the beta particle which is, by definition, an electron or a positron. Note that electromagnetic radiation like gamma rays (particles) and infrared radiation are not deflected in electromagnetic fields.
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