Question

How to get the electric power in each resistor when there's only one voltage in a circuit?

Answer 1

OK, hard to give a full answer without knowing the values of V and all resistor(s) or the circuit configuration, but I’ll give a theory-based answer.

Explanation:

The voltage dropped across each resistor depends on how they are arranged: in series the potential difference (p.d. or voltage) across each resistor is in proportion to that resistance. [e.g. for a p.d. of 6V two resistors of size 4`Omega` and 8`Omega` will get a p.d. of 2V and 4V respectively] In parallel circuits (with only one resistance in each branch) each one will get the full supply p.d. In combination circuits you need to apply both rules: first the parallel, then the series one.

Once you know the p.d. across each individual resistance you can find the power dissipated from `P = V^2/R` or find the current (using Ohm’s law `I = V/R`) then use `P = I^2R`