Question for electrical geniuses

[srfisher17]

About how many micro-amps would a multimeter need to register (from a power source) to run a small, 4watt, LED desk clock? Dumb question, I know, but I can't remember the whole amps-volts-watts- thing. I'm also to lazy, or too old (62), to get online and re-learn it. I'm become a real Wyle E. Coyote with this stuff. Thanks, I know our hobby attracts folks who are smarter than the average bear!!
BTW; yeah, its kid's science fair time. Finding this answer is my only contribution to my 6th grade Daughters project; all the parents that do all the work for these projects drive me nuts. I even know someone who had a professional graphics company do their kid's project...what a way to learn.

 

[bionicarm]

Originally Posted by srfisher17
http:///forum/post/3230144
About how many micro-amps would a multimeter need to register (from a power source) to run a small, 4watt, LED desk clock? Dumb question, I know, but I can't remember the whole amps-volts-watts- thing. I'm also to lazy, or too old (62), to get online and re-learn it. I'm become a real Wyle E. Coyote with this stuff. Thanks, I know our hobby attracts folks who are smarter than the average bear!!
BTW; yeah, its kid's science fair time. Finding this answer is my only contribution to my 6th grade Daughters project; all the parents that do all the work for these projects drive me nuts. I even know someone who had a professional graphics company do their kid's project...what a way to learn.
I=E/R
I=current (Amps), E=voltage, R=resistance.
Watts = Volts X Amps
4 watts = 120 volts X Amps
Amps = 4/120
Amps = .03333

 

[srfisher17]

Originally Posted by bionicarm
http:///forum/post/3230145
I=E/R
I=current (Amps), E=voltage, R=resistance.
Watts = Volts X Amps
4 watts = 120 volts X Amps
Amps = 4/120
Amps = .03333
Then .033333333333333333333 amps would be the answer need? I think a micro-amp is one-millionth of an amp. So, if I read about 2 microamps, it is too little, by a factor in the thousands? Right? Thanks!

 

[bionicarm]

Originally Posted by srfisher17
http:///forum/post/3230151
Then .033333333333333333333 amps would be the answer need? I think a micro-amp is one-millionth of an amp. So, if I read about 2 microamps, it is too little, by a factor in the thousands? Right? Thanks!
Move the decimal point over 6 places, so it's 33,333 uA.

 

[srfisher17]

Originally Posted by bionicarm
http:///forum/post/3230159
Move the decimal point over 6 places, so it's 33,333 uA.
Got it, Thanks!

 

[saxman]

i'm actually wondering what kind of meter you're using...most peeps don't have a microammeter or a picoammeter, and most "average" meters only range down into the milliamps, especially multimeters.
your meter would have to be showing 0.000XXX to be reading in the microamp range.
just curious...

 

[srfisher17]

Originally Posted by saxman
http:///forum/post/3231026
i'm actually wondering what kind of meter you're using...most peeps don't have a microammeter or a picoammeter, and most "average" meters only range down into the milliamps, especially multimeters.
your meter would have to be showing 0.000XXX to be reading in the microamp range.
just curious...
It is a multimeter.....so how many milliamps would 4 watts need? One milliamp=.001 amps, right?
My daughter is getting a reading of about 2....somethings...from a lemon. Would she be reading milliamps or microamps? Next year, her project better be something I know about; but that really limits the choices. Next year she does it herself--the way its supposed to be.

 

[scsinet]

She could be readnig in volts or amps, if she's reading "2 something" then it's probably 2ma (milliamps) or 2 mV (millivolts). Conventional multimeters don't read down to microamps.
If we are talking lemon batteries... when you say "LED Desk Clock" do you mean the type of clock that plugs in a wall outlet? If so, 4w at 120v = 33ma as the other said, but I think it was just assumed you were talking about an plug-in clock. If you are talking about lemon batteries, perhaps you mean something else... ??

 

[srfisher17]

Originally Posted by SCSInet
http:///forum/post/3231739
She could be readnig in volts or amps, if she's reading "2 something" then it's probably 2ma (milliamps) or 2 mV (millivolts). Conventional multimeters don't read down to microamps.
If we are talking lemon batteries... when you say "LED Desk Clock" do you mean the type of clock that plugs in a wall outlet? If so, 4w at 120v = 33ma as the other said, but I think it was just assumed you were talking about an plug-in clock. If you are talking about lemon batteries, perhaps you mean something else... ??
There are many reasons I don't like science fairs; the main one is that they make me feel like an idiot. But my son is a soph in college and majoring in math (weird, for a jock) and he still gets help from me....but anyway....it must be milliamps. Thanks, Guys!