Challenge Circuit 3

Real Inductor Circuit

Solution and Practical Results

In this post, I’ll show one of the ways of solving Challenge Circuit 3: Real Inductor Circuit and connect the circuit to get practical results. The real results are rarely same as the theoretical, but it’s good to compare how far off they are from each other. This can be quite useful for the students.

Here is the circuit from Challenge Circuit 3

Challenge Circuit 3 details

The values that were given are:

Supply is 15V 50Hz AC
By design, this Inductor has two components, where the resistive component is 18 ohms and the inductive component is 92mH

The challenge was to find

  1. The circuit current
  2. True power consumed by the inductor
  3. Power Factor of the circuit

Theory Solution

Here is one of the ways of solving the circuit above. This challenge is more involved than the previous ones, so I have broken it down into steps that I thought were the easiest for students to follow.

Circuit Connection and Measurement

As you would expect, the theory solutions can be different to the practical results, but calculations are a good place to start to understand a circuit. 

Here is a video of our circuit connection for this challenge circuit and the measurements.

Comparison: Theory VS Practical

Let’s compare the difference between the calculations and the measurement for this circuit

Value Theory result Practical result
The Circuit Current
0.44 A
0.442 A
True Power
3.49 W
3.6 W
Power Factor
0.53
0.546

Why is there a difference in the theory and practical values? 

There can be many reasons for this difference. Here are some of them that could be affecting the results in this circuit

  • Resistance of the inductor
  • Inductance value of the inductor
  • Power supply accuracy
  • Meter calibration

Let’s see a couple of reasons why we see the difference in results in this circuit

Resistor Theoretical Value Practical Value
Resistance of the inductor
18 ohms
18.4 ohms
Power supply voltage
15 V
15.1 V

The resistance of the inductor was considered to be 18 ohms during the calculation but when measured, the value was 18.4 ohms. This discrepancy in the value can affect the current, power and power factor.

There could be more reasons for these discrepancies, but these give us a good idea.

If you used a different method of solving this circuit or have other reasons for the difference in the theory vs practical results, please share it in the comments so our readers and students can benefit from your input.

Thanks for reading.

Husnen Rupani

Husnen Rupani

I help electrical training organisations increase learner engagement by designing innovative training equipment. I have a saying "Electricity - you cannot see, you cannot hear it, but by the time you feel it, it may be too late." My main aim is to turn this black magic that we call electricity into something that people can understand.