Parallel resistor question

[Regis]

Ok, say I parallel a pair of resistors while building an attenuator.

If I want say, 8 ohms, and parallel a 40 ohm and a 10 ohm to get it, will one or the other run hotter or soak up more or less current? Or cause other problems?

Would it be better to try and get the two more evenly matched?

Not sure if I am explaining this right.

Thanks guys

[JoeM]

Two 4 ohms in series or two 16 ohm in parallel would be better (if you only want to use two resitors), each resistor will dissipate the same amount. How much power do you need to dissipate?

[Albert Kreuzer]

The 10 Ohm resistor will dissipate 80% of the power, the 40 Ohm 20%. Otherwise, no problem.

[Regis]

Thanks guys, I thought it was something like that. For this particular attenuator, it's only about 15 watts.

Albert, what formula is used, or how did you figure the 80/20 ratio?

Thanks again

[defaced]

Ohm's Law (V = I*R) and then the electrical power equation (P = V*I). Rearrange as needed to get the formulas in a form you want, but after some Algebra, you can get P = (V^2)/R. So figuring both have 10 volts across them (just for a nice round number), you get 10w for the 10R resistor, and 2.5w for the 40R resistor. 10w is 80% of the 12.5w total and 2.5w is 20% of the 12.5w total.

[Albert Kreuzer]

Exactly. Mike was faster

[Regis]

thanks again, good stuff