New York State Master Electrician Practice Exam

When three resistors are connected in series and an amperage of ten amps is achieved, how does the ampere reading change when an equal resistor is added in parallel?

1. It doubles

2. It remains the same

3. It increases slightly

4. It decreases

The correct answer is: It doubles

When three resistors are connected in series, the total resistance is the sum of the individual resistances. The current flowing through a series circuit is the same across all components, so if the amperage is ten amps with three resistors, that represents the total current flowing through the circuit. When an additional equal resistor is added in parallel to the existing resistors, the total resistance of the circuit changes. In a parallel connection, the effective resistance decreases because the current can split and flow through multiple paths. The formula for calculating the equivalent resistance of resistors in parallel is: \[ \frac{1}{R_{total}} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3} + ... + \frac{1}{R_n} \] In this case, since one resistor is added in parallel, the total resistance decreases compared to the series arrangement. As the total resistance decreases, according to Ohm's Law (V = I × R), for a constant voltage source, the current must increase in order to maintain the relationship defined by Ohm's Law. Therefore, with the new resistor in parallel reducing the total resistance, the overall current in