Concept explainers
* Two compass needles are fixed at the ends of a straw (the north pole of one needle is placed above the south pole of the other needle) and are hung at the end of a light string as shown in Figure P20.6. The needles are brought close to a long horizontal wire connected to a circuit, as shown in the figure. (a) How will the needles point after the switch is closed? Explain. (b) Your friend claims that Earth's magnetic field does not affect the two-needle device. Do you agree or disagree? Explain your reasoning.
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