A telegraph circuit is a large loop. Electricity flows from the sender to the re

Question

A telegraph circuit is a large loop. Electricity flows from the sender to the receiver through a long wire on the surface of the earth, then back from the receiver to the sender straight through the earth. Over a century ago, just before the American Civil War, the transatlantic cable (crossing the Atlantic Ocean) was completed, making the biggest electric loop in the world. Often, strange "ghost signals" were heard through the cable, when messages were not being sent. After much investigation, these signals turned out to be attributed to (choose one, then explain your choice) :

a. thermal variations in the cable

b. fluctuations in the earth's electric field

c. fluctuations in the earth's magnetic field

d. iron ships

e. ghosts

Explanation / Answer

(c) Fluctuations in earth's magnetic field.

Because according to lenz's law , whenever there is change of magnetic flux throught the closed loop , the current will be induced in the circuit to nullify the effect.

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