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Before World War II, some radios got power through a
Chapter 21, Problem 11(choose chapter or problem)
Problem 11CQ
Before World War II, some radios got power through a “resistance cord” that had a significant resistance. Such a resistance cord reduces the voltage to a desired level for the radio’s tubes and the like, and it saves the expense of a transformer. Explain why resistance cords become warm and waste energy when the radio is on.
Questions & Answers
QUESTION:
Problem 11CQ
Before World War II, some radios got power through a “resistance cord” that had a significant resistance. Such a resistance cord reduces the voltage to a desired level for the radio’s tubes and the like, and it saves the expense of a transformer. Explain why resistance cords become warm and waste energy when the radio is on.
ANSWER:
Solution 11CQ
A transformer is a device used for step up or step down the voltage supply, to the desired value.
In this case, the voltage is desired to cut down to a level, matched to power up the radio set. So the resistance cord is used as supply cable as well as a device to cut down the voltage supply.
As the cord has a resistance of its own, so when the current pass through it, certain amount of voltage drop will be take place as,
V =I R
Here, V is the voltage, I