Question

Those fifty 15 ohm parallel connected Christmas tree lights. Calculate the total current in the circuit if they are connected to a 115 VAC source.​

Answer 1

If you have fifty 15-ohm resistors all connected in parallel, their "effective" resistance is (15/50) = 0.3 ohms.

Current = (voltage) / (resistance)

Current = (115 V) / (0.3 ohm)

Current = 383.3 Amperes

This is an interesting question, with a VERRRRY interesting answer.  The fuse or circuit breaker that feeds the outlet where these lights are plugged in is most likely rated 15 or 20 or 25 Amperes, and it trips immediately.

But let's say it doesn't ... let's say the juice just keeps on flowing.

Power = (voltage) x (current)

These lights use energy at the rate of (115V)x(383.3A) = 44,083 watts.  This is roughly the same as the power used to run 22 toasters or 37 blow-dryers, all at the same time.  AND ... the lights are going to produce almost as much heat as 22 toasters or 37 blow-dryers all running at the same time.  The lights will probably burn the house down before long.

If electrical energy costs 20¢ per kilowatt-hour in this city, then running those lights for ONE HOUR is going to cost $8.82 !

All in all, it will be a good idea to unplug the Christmas tree lights when the family goes to bed.