You and a friend are studying for an exam and the session goes until the early m

Question

You and a friend are studying for an exam and the session goes until the early morning. At about 4 am you decide to cook some breakfast. Despite being sleepy you've got the coffee perking. Now you want to make some waffles but you realize there might be a problem. The 1000-watt waffle iron and the 600-watt coffee maker are plugged into the 110 V kitchen electrical outlets. If you plug in your 700-watt blender, will you overload the 20 A circuit breaker? The circuit breaker protects those kitchen circuit wires that have the most current from carrying too much current. You are trying to figure out how the electrical outlets are connected together in a circuit when your friend reminds you that when you disconnect the coffeepot, the waffle iron stays on. Now everything is clear.

Explanation / Answer

Consider the fact that the waffle iron and coffee maker are connected parallel across a common potential difference of 110 V. Let us again consider that blender can also be connected parallel to the previous connection. It is given that there is a 20 A circuit breaker connected to the system of devices. Any current greater than 20 A drawn from the parallel connection will cause the 20 A breaker to break and disconnect the flow of current. Thus, the current drawn should be smaller than 20 A to avoid overload in the 20 A breaker.

Power is equal to potential difference times current. Thus, current is equal to power divided by potential difference.

Now, the current drawn from the 1000 W waffle iron is

I1 = 1000 W / 110 V

    = 9.0909 A

The current drawn from the 600 W coffee maker is

I2 = 600 W / 110 V

    = 5.4545 A

The current drawn from the 700 W blender is

I3 = 700 W / 110 V

    = 6.3636 A

The breaker will break if the total current drawn from the three devices is greater than 20 A.

Thus,

I1 + I2 + I3 = 9.0909 A + 5.4545 A + 6.3636 A

                  = 20.909

                 > 20 A

Thus, the current flows in the breaker is greater than 20 A if the 700 watt blender is used.

Therefore, there will be overload in the 20 A breaker if the 700 watt blender is plug in.

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