Ohms Law

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It was all part of the energy savings act along with the phase out of incandescent lamps. As part of that act, to get people to save energy, bulbs labeled as 60 watt officially became something like 43 watt lamps.


You can see the schedule here


https://www.bulbs.com/learning/phaseoutschedule.aspx

Edit:

Yes the hot vs. cold resistance will make the biggest difference. But even if you could measure the hot resistance, you would still be off by the 43/60 watt ratio.
 
Yes the hot vs. cold resistance will make the biggest difference. But even if you could measure the hot resistance, you would still be off by the 43/60 watt ratio.

You just had to throw that 43/60 in there. I was feeling good with the answers now tell me how you got 43/ 60
 
190130-2452 EST

Dennis:

From responses you provided I don't see that you really understand what is happening.

Get a Variac and do some tests. But even without the Variac measure the room temperature resistance of a 100 W tungsten bulb with a Fluke DVM.

Another simple test to do is a V, I measurement with a 100 W 120 V tungsten bulb connected to a 12 V car battery.

Relative to inrush current see my first two plots at http://beta-a2.com/EE-photos.html .

.
 
190130-2452 EST

Dennis:

From responses you provided I don't see that you really understand what is happening.

Get a Variac and do some tests. But even without the Variac measure the room temperature resistance of a 100 W tungsten bulb with a Fluke DVM.

Another simple test to do is a V, I measurement with a 100 W 120 V tungsten bulb connected to a 12 V car battery.

Relative to inrush current see my first two plots at http://beta-a2.com/EE-photos.html .

.

gar, do you have a spare Variac I can borrow? Oh, wait! Darn Amazon has everything!

41xkJGA7QbL.jpg
 
190201-0525 EST

Gary11734:

If you don't have a Variac, then a 12 V volt battery is a convenient low voltage source, most people will haver a car or truck, provides a low enough voltage to see a point between 0 V and 120 V that will show a large resistance change. Or put 10 100 W bulbs in series. Another possibility is a 15 W in series with a 100 W supplied from 120 V.

.
 
190201-0610 EST

100 W tungsten bulb at 12.4 V DC is 0.25 A or 49.6 ohms and a very dim glow.

Might be able to run a variable voltage test with a Lutron CL dimmer adjusted for maximum phase shift range and use of good RMS meters. I don't believe you can get as low as 12 V.

.
 
It was all part of the energy savings act along with the phase out of incandescent lamps. As part of that act, to get people to save energy, bulbs labeled as 60 watt officially became something like 43 watt lamps.


You can see the schedule here


https://www.bulbs.com/learning/phaseoutschedule.aspx

Edit:

Yes the hot vs. cold resistance will make the biggest difference. But even if you could measure the hot resistance, you would still be off by the 43/60 watt ratio.

We, the Besoeker houshold, use LED lights. The spotlights in the kitchen are GU10 5W, 3000k coour which is bright white.
 
190201-0610 EST

100 W tungsten bulb at 12.4 V DC is 0.25 A or 49.6 ohms and a very dim glow.

Might be able to run a variable voltage test with a Lutron CL dimmer adjusted for maximum phase shift range and use of good RMS meters. I don't believe you can get as low as 12 V.

.

OK, but I'm not sure what this experiment is intended to demonstrate?
 
Dennis, a complete version of Ohms Law states that an electric current in a closed circuit or loop will increase when the voltage increases or will decrease when the voltage decreases provided the resistance of the circuit does not change.

Most versions of ohms law, especially the simplified math version (E=IxR) leave out two critical statements that allows one to know if the formula application is valid. Those two statements are in bold text above. If the measured value does not match the calculated value those statements can provide valuable clues as to why the desired results were not achieved.
 
You just had to throw that 43/60 in there. I was feeling good with the answers now tell me how you got 43/ 60

Since the general public doesn't know what a lumen is (i.e. the SI unit of brightness), the energy efficient bulbs get compared to something that people actually can relate to, which is the incandescent bulbs that the newer bulbs replace. Incandescent bulbs burn a lot of their energy as infrared radiation, which the human eye can't see. Newer bulbs are built to emit less of this, and the same visible light, as their incandescent counterpart corresponding to the Watt-equivalent rating.
 
I believe he is trying to demonstrate the resistance curve of the tungsten lamp as it heats up. Measuring V & I across the range of the Variac would do this.
I agree, it would. But you can calculate the hot resistance from rated voltage and power. A regular DVM will give you the cold resistance. The RTC of tungsten gives you intermediate values between cold and operating temperature which is around 2500C.
 
I agree, it would. But you can calculate the hot resistance from rated voltage and power. A regular DVM will give you the cold resistance. The RTC of tungsten gives you intermediate values between cold and operating temperature which is around 2500C.

Agree - I suspect he thought a hands-on experiment would more useful to drive home the concept in this case.
 
You just had to throw that 43/60 in there. I was feeling good with the answers now tell me how you got 43/ 60


We use the 60 watts as a fixed known. Then, this happens!

Based on the new information, 43/60. I would energize this light. Let it get to operating temperature, then put an amp probe on it.

Now you can determine what the true resistance is at operating. And, what the wattage is.

Also, you can now measure the resistance cold and see the difference between room temp and operating resistance for clarity.
 
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