# 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!**