Astring of 27 identical christmas tree lights are connected in series to a 120 v source. the string dissipates 68 w. what is the equivalent resistance of the light string? answer in units of ω.

The power dissipated by the whole string of tree lights is:

where 
V is the potential difference of the whole circuit
I is the current flowing through the tree lights.

By using P=68 W and V=120 V, we find the current:


Ohm's law for the whole string of tree lights is:

where  is their equivalent resistance. Re-arranging the equation, we find the value of the equivalent resistance: