Question

A string of 5 (Five) 15 ohm Christmas tree lights are connected in parallel. One burns out, the rest will stay lit. Calculate the total resistance when one of the bulbs is out.

Pt 2.

Those five 15 ohm, series connected Christmas tree lights, calculate the total current in the circuit if they are connected to a 115 V source. What would be total power?

Pt. 3
Those five 15 ohm parallel connected Christmas tree lights. Calculate the total current in the circuit if they are connected to a 115 V source. Calculate total Power.

Please list formula and data etc etc

Answer 1

r = 15 ohms for a single bulb

1 / R = 1 / r + 1 / r + 1 / r + 1 / r

R = r / 4 = 15 / 4 = 3.75 ohms total resistance

part II

If bulbs are in series R = 5 * 15 ohm = 75 ohm total resistance

P = I V = V / R * V = V^2 / R

P = 115^2 / 75 = 176 watts

part III

If the bulbs are in parallel then

R = 15 / 5 = 3 ohms for the circuit

I = 115 / 3 = 38.3 amps for circuit

P = 115^2 / 3 = 4400 watts

Check: P = I V = 38.3 * 115 = 4400 watts