Calling all electrical experts! Please help an idiot!

J_F said:
wattage is a calculation, it's not measured
he's suggesting it's very difficult to measure the resistance of a lit incandescent bulb
but with an ammeter, you can see the lit amps, and calculate you watts

those microscopes were mechanical, eh?
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Watts are measured based on time, how do you think the hydro company knows how much to charge you in kilowatts per hour :LOL:
Turn everything in your house off and go look at your hydro meter, now turn on one light bulb. Wow, we are measuring wattage.
No, microscopes are largely optical with a good portion of mechanical and electronic related parts and accessories, then there is all the other scientific and medical equipment you would need to google to know what it even did.

"The watt (symbol: W) is a unit of power. In the International System of Units (SI) it is defined as a derived unit of 1 joule per second,[1] and is used to quantify the rate of energy transfer."
 
the meter does the calculation then expresses that over time
it does not measure watts

I'm not getting sucked into this crap again
go on believing you're more clever than everyone else

cheers
 
UHmmmmmm
Watts = volts x amps
Pretty simple. It's measurement of energy.

Ya wanna know how many watts a bulb is?
Set your multi meter to amps, put in a serial circuit with the bulb. Now ya know amps.
Measure the voltage at the power supply. Now ya know the voltage.

I don't know how time would be involved.
Joules are the metric equivalent measurement, but it's metric so it makes more sense. It takes 1 joule of energy to raise one cc/ml of water one degree centigrade
Watts x time would be Horse power. Horse power is a dumb measurement.
 
Trials said:
Watts are measured based on time, how do you think the hydro company knows how much to charge you in kilowatts per hour
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Hows 'bout
Kilowatts used divided by Hours to use them
I'm pretty sure that'll get ya' kilowatts per hour.
... or am I missing something? I got taught "NEW MATH"

... or are you thinking about "usage rates"? Which is different than straight kilowatt hours
 
An incandescent bulb is a fancy resistor.

The resistance of a resistor is a function of its temperature. For a normal resistor that you see soldered onto a circuit board, this isn't significant, but given the very high operating temperature of an incandescent filament, the resistance at operating temperature (bulb lit) will not be the same as it is when the bulb is cold. The resistance when the bulb is cold will be lower. So ... for a fraction of a second after being switched on that it takes for the filament to get up to operating temperature and start glowing ... that "5 watt" (at operating temperature) bulb will pull more current and therefore more power. It also means that if you measure the resistance of the bulb with an ordinary multimeter with the bulb not turned on, you will get a falsely low measurement that doesn't represent what the resistance actually is with the bulb switched on and the filament hot and glowing.

Having said that ... all incandescent bulbs are designed for the filaments to be in pretty close to the same temperature range and they all use tungsten filaments, so it will be off by a predictable factor. And that is ...


Note that the resistivity at room temperature is much lower than at operating temperature (about 2700 - 2800 K) which implies that a bulb will have a pretty high inrush current (due to resistance being much lower at ambient temperature than at operating temperature). But a tungsten filament has very low mass - the resulting inrush current will very quickly heat the filament and thus increasing the resistance so that the inrush current quickly drops towards normal operating current.
 
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Glad I haven't said anything incorrect yet :unsure:
Yes, kilowatts per hour would be a rate much like would be used to calculate your hydro bill :| you pay for watts, it represents spent energy.
 
Trials said:
what on earth are you on about :unsure: it's a light bulb not a space shuttle booster rocket seal.
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OK I have just measured the resistance of a light bulb in my hands. The resistance of the bulb was 50 ohms. It's a 120 volt bulb so according to you and ohms law it should draw 2.4 amperes, A = Voltage divided by resistance. The output (2.4 amps X 120 volts) should be 288 watts. However the bulb is only 25 watts.

That is because the resistance of a conductor rises with temperature and the white hot filament of the bulb takes that to the extreme.

It is very difficult to measure the resistance of an operating device because an ohmmeter typically blows a shunt if connected across a voltage. I learned that the hard way seeing the puff of smoke float up out of the meter when the case was opened.

In reality the 25 watt, 120 volt bulb would draw about 0.2 amps. That would mean the calculated hot resistance would be 576 ohms (120 divided by 0.2).

You might note that, going the other temperature direction, superconductors tend to run at absolute zero or thereabouts.

Read up on temperature resistance coefficient. It's not rocket science.

Physics joke. The researcher fell into a vat of liquid nitrogen. He's OK now.
 
Trials said:
Watts are measured based on time, how do you think the hydro company knows how much to charge you in kilowatts per hour :LOL:
Turn everything in your house off and go look at your hydro meter, now turn on one light bulb. Wow, we are measuring wattage.
No, microscopes are largely optical with a good portion of mechanical and electronic related parts and accessories, then there is all the other scientific and medical equipment you would need to google to know what it even did.

"The watt (symbol: W) is a unit of power. In the International System of Units (SI) it is defined as a derived unit of 1 joule per second,[1] and is used to quantify the rate of energy transfer."
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As you indicate, a one kilowatt device run for an hour will get you a bill for one kilowatt hour of electricity, plus various surcharges, debt retirement fees, taxes and account fees.

Your meter watching comment reminded me of a client with a 30 KW snow melting system.

He was in the process of moving into the house so electrical usage was next to nothing. However he had turned the snow melting on to keep the driveway clear in case they had to transport something. He asked how much power the system consumed.

Since we were standing by the meter and the snow melting switch I pointed out that the wheel was barely turning, being turned off for testing. Then I flicked the switch and the wheel just about spun a bearing. His face turned white. The system had been on 24/7 for about three weeks.
 
Glad I kept a low profile. You guys can drive each other nuts. ;)
 
imagine if it was something complicated
:ROFLMAO: a 30 cent light bulb :ROFLMAO:
 
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