Hey so im stuck on a 2part question, it goes as follows: A tungstan filament in a light bulb is rated 75w for a 230v supply. The resistance of the filament at 20*C (*C means degrees celcius) is 68 ohm. Assume a constant temperature coefficient of 0.005. Calculate: A) The hot resistance of the filament Ok so I have no idea what temperature to use for "hot" so I used 100*C (I mean thats hot!:tongue2: ) Then used the equation R1=R0 (1+0.005x100) - Where R1= Resistance at 100*C R0= Resistance at 20*C 0.005= Temperature Coefficient 100= 100*C "Hot" temperature. If you work this out it gives you a resistance of 102ohm @ 100*C. I think that bit is right but is the 100*C right? I have a second part to this so I'll put it in a different colour to help.... B) The operating temperature of the filament? Well for this one I was going to use the formula (T1= R1/R0-1 All Divided By 0.005) But turns out that gives you an operating temp of 100*C .... yea im lost and have googled looking for operating temperature formulas...Help! Thanks People!!