# FireFighter Aptitude Test Tuesdays – Electrical Circuits

Every Tuesday I post a common question you might encounter during your firefighter aptitude test. This week we will be covering electrical circuits.

For more questions, have a look at the Firefighter Practice Tests – Premium Pack. They offer over 99 practice tests and over 1500 questions.

The Problem:

The circuit shown in the following figure has three resistors, R1 = 3Ω, R2 = 6Ω and R3 = 9Ω. If all of the resistors used in the circuit shown is designed to operate at a maximum of 4 Amperes, which of the three resistors may fail?

1) All resistors will fail
2) R1 will fail
3) R2 and R3 will fail
4) No resistors will fail

The Solution:

The correct answer is #2, R1 will fail. Here is how:

If the current passing through a resistor is higher than its designed capacity, the resistor would fail.

Let us first find the value of current passing through each resistor.

Use the Ohm’s law:

The current flowing in any resistor is inversely related to its resistance value.

I = V/R

All of the resistors have a voltage V = 18 Volt across their terminals.

So,

I1 = V/R1 = 18/3 = 6 Amperes

I2 = V/R2 = 18/6 = 3 Amperes

I3 = V/R3 = 18/9 = 2 Amperes

Current I1 passing through the first resistor is higher than its design capacity. Therefore, R1 will fail.

What would you like me to solve next week? Leave your comment below!

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