The total current delivered to a number of devices connected in parallel is the

Question

The total current delivered to a number of devices connected in parallel is the sum of the individual currents in each device. Circuit breakers are resettable automatic switches that protect against a dangerously large total current by "opening" to stop the current at a specified safe value. A 1670-W toaster, a 1040-W iron, and a 1300-W microwave oven are turned on in a kitchen. As the drawing shows, they are all connected through a 20-A circuit breaker (which has negligible resistance) to an ac voltage of 120 V. (a) Find the equivalent resistance of the three devices. (b) Obtain the total current delivered by the source and (c) determine whether the breaker will ?open? to prevent an accident (yes or no).

Explanation / Answer

Power = V^2/R

Toaster => 1670 = (120)^2/R
R(toaster) = 8.62
R(iron) = 13.85

R(microwave) = 11.08

b) Net resistance of the circuit = 1/(1/R1 + 1/R2 + 1/R3) = 3.59

Current = 120/3.59 = 33.42 Amp

c) Yes the circuit will open

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