# An odd electronics test question

Discussion in 'Electronics Homework Help' started by Xaos, Apr 9, 2012.

1. ### Xaos

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Jun 13, 2011
An odd electronics test question (SOLVED)

I could really use some help. I am taking an electronics test, and this is one of the questions:

Direct current would NOT ordinarily be used in which of the following?
A. Ships
B. Airplanes
C. Battery Charging
D. Arc Welding
E. Electric clocks

Now I may be totally crazy, but don't all on the list use or are capeable of using both AC & DC? I've pretty much narrowed this down to either battery charging or arc welding, but both of these have AC & DC versions... Battery chargers are typically run on AC, but output DC, though there are the 'quick charge' packs that use entirely dc...

Any help appreciated.

Last edited: Apr 12, 2012
2. ### davennModerator

13,798
1,939
Sep 5, 2009
hi Xaos

interesting question, I wonder how much googling you have done on each of the possible answers ?
you have to look closely at the question and in particular the way its worded.

.... NOT ordinarily.....

I learnt a few things myself when I googled the options.... particularly that in several cases tho DC is used AC is the primary power source.

have a bit of a google ... particularly on the first 2 options then we can compare notes

cheers
Dave

3. ### Xaos

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Jun 13, 2011
Actually through extensive research and picking the brain of everyone, I'm leaning towards electric clock.

The reason being is that this test is quite old (I would say 60s due to the fact that part of the test deals with thyratrons used as rectifiers, a long outdated concept). There can be only one correct answer, so ships and airplanes are too general and similar in propulsion concept to choose between one and the other, plus pretty much anyway you look at it, they use both AC & DC voltage in one way or the other. Arc welders, historically, were first made using DC before their AC counterparts came out. Batteries are DC and thus the charging of them will always involve DC. Electric clocks (up to the probable time of this test) used AC oscillation to keep an accurate time, prior to quartz movement.

as hereElectric Clocks

Thanks very much for help.

Last edited: Apr 12, 2012