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 1700 W toaster, a 1050 W iron, and a 1250 W microwave oven are turned on in a kitchen. As the drawing shows, they are all connected through a 20 A circuit breaker to an ac voltage of 120 V. a) find the equivalent resistance of the 3 devices. b) obtain the total current delivered by the source. c) will the breaker open to prevent an accident?

Explanation / Answer

1. P = v2/r

1700 = 1202/R R = 8.47

1250 = 1202/R R = 11.52

1050 = 1202/R R = 13.71

equivalent resistance = 1/(1/8.47 + 1/11.52 + 1/13.71) = 3.6

2. total current = 120 V / 3.6 = 33.33 A

3. the breaker will trip, 33 > 20

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