# 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...

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 acgainst large current by opening to stop the current at a specified safe value.

A 1650W toaster, a 1090W iron, and 1250W microwave turned on. They are all connect through a 20A circuit breaker to a 120V power supply.

How do I calculate the equivalent reisistance of the three devices.

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### 1 Answer

A 1650W toaster, a 1090W iron, and 1250W microwave turned on. They are all connect through a 20A circuit breaker to a 120V power supply.

Let respectively current in each device respectively toaster ,iron and microwave be `I_1,I_2, and I_3.` The resistance of each device be respectively `R_1,R_2, and R_3.`

We know work done by electrical energy is `H=I^2RT` ,where T is Time in hours electrical energy used. So

we have

`I_1+I_2+I_3=20 A` (i)

Also

`1/R_1+1/R_2+1/R_3=1/R` (ii)

where R is equivalent resistance of the three devices.

`R_1=1650/(I^2_1)`

`` `R_2=1090/(I^2_2)`

`R_3=1250/(I^2_3)`

Also `R<=(120/20)=6`

Using above relations we can calculate the equivalent resistance.