Question

A string of 14 identical Christmas tree lights are connected in series to a 124 V source. The string dissipates 70 W. What is the equivalent resistance of the light string? Answer in units of Ω.

Answer 1

V=IR

P=VI=V^2/R

R(total)=14R

70W=(124V)^2/14R

R=124^2/14*70=15.7omhs per light

R(total)=14R=219.6omhs=220ohms total equivalent resistance of the light string