# Homework Help: Ohms law question?

1. Jan 9, 2008

### samblue

1. The problem statement, all variables and given/known data

Define resistance and resistivity? A 30W, 6A bulb has a filiment which is directly prortional to the absolute temperature? At 37 degrees celcius the reisitance of the fimament is 015ohms. What is the working temperature of the filament?

2. Relevant equations

None given. But from my attempt I have used V=IR, P=IV.

3. The attempt at a solution

Resistance is a measure of a materials ability to pass charge. Reisistivity is a constant for each material which allows us to calculate the resitance, thus it is the ability for a material to pass current.

Ok so I worked out the current using P=IV
getting: I=6A

I then used this to work out the resistacne using V=IR
getring R=1.2ohms.

Im stuck here and dont know what to do, can someone please give me some hints or a rough idea about how to go about solving this problem? thanks

2. Jan 9, 2008

### Shooting Star

> A 30W, 6A bulb has a filiment which is directly prortional to the absolute temperature?

This question should be a statement and has got something missing -- probably that the resistance is directly prortional to the absolute temperature. Please verify.

3. Jan 9, 2008

### samblue

sorry. its the resistivity which is directly proportional to the absolute temperature.

4. Jan 9, 2008

### Shooting Star

You know the R at the working temp T -- you've solved it. You also know R at 37 C. Any ideas?

5. Jan 9, 2008

### samblue

No sorry i dont. I know this is almost certainly something simple which will make me feel stupid when I see the answer but at the moment I dont have the figgiest. My best guess would be to assume that the reistance and the temperature are related linerly?

6. Jan 9, 2008

### Shooting Star

Why would that be your guess? It's GIVEN in the problem, in the sentence you had mistyped. Refer post #3.