Basic basic electrical question (Ohm's law)
 

What am I doing wrong here guys-

I have a tiny auto light bulb and want to know its wattage so I can go shopping.

It draws 120mA as measured by an in-serries ammeter at 12VDC. Ohms law says that means it is approx. a 1.44 watt bulb and its resistance is 100ohms.

But measured filiment resistance is 9.5 ohms...huh? What's wrong here?

Try a diffrent DVOM.

Thats all I can think of.

As the wire heats and glows, the resistence goes up.

Oh yeah thats right. I forgot about that.

Red-beard -so it's normal that cold resistance would be that low and the 1.44W calc is OK? Thanks.

Re: Basic basic electrical question (Ohm's law)
 

What does the manual call for in the position the bulb goes in? You're not working on a car without a maintenance manual open are you?

http://www.geocities.com/SiliconValley/Circuit/1858/resiscale.htm

Yes it is normal.

I used to know that, but I never need to use some of that knowlege anymore. so you know, it gets forgotten.

The nominal wattage may be 2 watts. Where is the bulb located? The speedo/guage cluster?

Also remember, car are 12v nominal, 13.8V at the battery and about 15vdc when charging.

It's a bulb from the 3rd brake light array on my 993. It's a little one, and there are 20-something of them.