This is a 3-part problem of which I have solved 1 and 2. I've included here just so you can follow the problem. A 50-watt lamp, a 20-watt, a 75 watt lamp, and a 100-watt lamp are connected in parallel to a 110-volt circuit. Calculate a) the current through each lamp; b) the resistance of each lamp; c) the total resistance of the circuit.
The Attempt at a Solution
a.) Current is calculate by I=P/V where P is in Watts so
I=50/110 = .45 A
I=20/110 = .18 A
I=75/110 = .682 A
b.) Here we use Ohm’s Law again: R = V / I
For 50 Watt lamp R=110/.45 = 244.4 Ω
For 20 Watt lamp R=110/.18 = 611 Ω
For 75 Watt lamp R=110/.682 = 161.29 Ω
For 100 Watt lamp 110/.91 = 120.88 Ω
c.)To find total resistance of the circuit in parallel, use
R=1/(1/244.4) + (1/611) + (1/161.29) + (1/120.88) = 49.5 Ohms
I've seen many ways to calculate resistance - but is it accurate to do it this way for a parallel circuit?