# Homework Help: Resistors! physics question

1. Apr 14, 2010

### knobles8179

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

A 2.7 kOhms and a 3.8 kOhms resistor are connected in parallel; this combination is connected in series with a 1.5 kOhms resistor.
If each resistor is rated at 0.9 W (maximum without overheating), what is the maximum voltage that can be applied across the whole network?

2. Relevant equations

parallel resistors 1/Req = 1/R1 + 1/R2 + 1/R3 ...
resistors in a series Req = R1 + R2 + R3 +...
Vab = E- IR
I= V/Req

3. The attempt at a solution

2. Apr 15, 2010

### rl.bhat

Re: Resistors!

Using the formula for wattage
w = I^2*R, find the current in resistance in series.
This is the current drawn from the battery.
Using this current, check the wattage of the individual resistance in the parallel combination. If it is less than 0.9 W, proceed further to find the total resistance of the circuit. Then V = I*Req.
If not, find the current in the individual resistance in the parallel combination for 0.9 w dissipation. Take the minimum current for finding the maximum voltage supply.