Finding the resistance value and total

Question

Two incandescence 50w-220v connected in series, then the two lamps are connected in parallel with incandescent lamp an 80W, 220V

A ) how the obstacles total?

B ) how power produced all the joint if connected to voltage 110v?

Answer 1

This is a little hard to follow (I guess it was translated?), but I'll try.

a) I think you're asking for the total resistance of the lamps. Try this:

1. For each lamp, solve for the resistance using a formula that relates power (P), voltage (V), and resistance (R). P = V²/R. Do this for all 3 lamps first (2 of them are the same of course).
2. Recall that resistors in series can simply be added together. So, for the 2 resistors in series, just add them up. You could call this R₁₊₂ if that helps.
3. Parallel circuits are trickier. Here, the general formula is 1/R_eq = 1/R_a + 1/R_b + 1/R_c + 1/R_d ... etc. We only have 2 branches to this parallel circuit, so it's not too bad.
4. You are solving for R_eq. One of your R values comes from the value you just found for R₁₊₂, and the other comes from the 80W/ 220V lamp
5. CAREFUL: The value that you find for R_eq MUST be lower than the resistance in each branch of the parallel circuit.

b) This is the easier part. Go back to the formula for Power, P = V²/R. But now, instead of using it for individual resistors, you're using it for the circuit as a whole. You just found the R value, and V is given as 110 V. So, just plug in to find the total power (in Watts) for the circuit.