Basic electrical lesson

[dave1949]

I have a dryer that has a dial that goes to eleven.
Can I play in this conversation?

Only if it also has a "damp dry" setting. :laughing:

 

[xtn]

Thank goodness. :laughing:

To be picky, I didn't think my original sentence was all that bad. The discussion was about the electricity cost of operating a clothes dryer.

If I had included the implicit information such as: "[Operating a dryer rated at] 7200 watts per hour [of use] = 7.2kWh." Would I still be guilty?

Ahhhhh... the difference context can make, huh? It would still be clearer if you just said "operated for an hour." Hmmmm, I wonder if sentences like yours are the real reason people so commonly get it wrong. I mean your sentences is technically accurate, but then some guy's going to later try explaining to his wife and what she's going to hear is "7200 watts per hour = 72 kilowatt-hours."

 

[CobyRupert]

I have a dryer that has a dial that goes to eleven.
Can I play in this conversation?

- Yes Nigel. Why didn't you just make the 10 setting hotter?

 

[dave1949]

Ahhhhh... the difference context can make, huh? It would still be clearer if you just said "operated for an hour." Hmmmm, I wonder if sentences like yours are the real reason people so commonly get it wrong. I mean your sentences is technically accurate, but then some guy's going to later try explaining to his wife and what she's going to hear is "7200 watts per hour = 72 kilowatt-hours."

It sounds like I'm still guilty of something. Nothing new there. :laughing:

 

[CobyRupert]

A beautiful mind?

Ha ha, true story, I guess there is some similarity, though I never won any Nobel Prizes or went to MIT.

 

[troutsqueezer]

Ha ha, true story, I guess there is some similarity, though I never won any Nobel Prizes or went to MIT.

Technically, that would be "NOR went to MIT". :laughing:

 

[JerryK]

In the sixties, before I got to go play in Vietnam, I was taught that the holes flow from Positive to Neg, and the electrons flow from Neg to Pos... [ so there, pppppppppffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffftt ] [ I assumate that raspberries are allowed on this forum.. ]

 

[CobyRupert]

It gets confusing because nobody knows what a Joule of energy is, or the relationship between (total) energy, (instant) power and time.
A Watt is the power being applied in that instant, whereas a Joule represents the total energy required, regardless of time. See, a Watt already has a time component in it, in that 1 Watt= 1 Joule/sec. Or conversely, consuming 1 Watt for 1 second = 1 Joule of total energy used.
(Example: It might take 100 joules of total energy to pick up a rock into a truck. You can use a 25 watt motor (and gears/pulleys) to do it in 4 seconds, but you would need a 200 Watt motor if you wanted to do it in a 1/2 sec. Understand?

So when you talk about 7.2 kilowatt-hours, that is the (total) energy that 7200 Watts (of instantaneous power) consumes in an hour. (Or 7200 Joules/sec x 3600seconds = 25.9 mega joules (or about 24,000 BTU's using imperial uits), but nobody says " Hey the electric bill last month was 25.9 mega-joules, cause it would be even more meaningless than saying it's 7.2 kilowatt-hours."

Its a way of using units that don't make logical sense but are familar, sort of like answering "How far is it to the dealer?" With "About an hour if you drive the speed limit" [Hint: An hour is not a unit of distance!- pet peeve!]

 

[CobyRupert]

Technically, that would be "NOR went to MIT". :laughing:

See, that proves my point. :laughing:

 

[mikehaugen]

Imagine my surprise when I first heard a boiler rated in hp. I know it's the type of measurement, but it seemed strange. Hmm... makes me wonder how my tractor's 38 hp converts to btus/hr.

Not quite electrical I know, but I thought it was relevant nonetheless.