Challenge Circuit 1

LET DC Circuit

Solution and Practical Results

In this post, I’ll show one of the ways of solving Challenge Circuit 1: LET DC Circuit and connect the circuit to get practical results. Real results are very rarely the same as the theoretical; we will compare how far off they are from each other. 

Here is the circuit from Challenge Circuit 1

Challenge Circuit 1 details

The values that were given are:

A = 2 ohms
B = 5 ohms
C = 39 ohms
D = 20 ohms
Voltage across the circuit = 20V

The challenge was to find the current through resistor C, voltage across resistor D and the total power of the circuit.

Theory Solution

When it comes to solving a circuit, there may be many ways to do it. Here I’ll show you one of those ways. I have broken it down into steps that I thought were the easiest for students to follow.

Circuit Connection and Measurement

As we can understand, the theory solutions may not be the same as the practical results. In fact, in most cases, they differ slightly and in some cases, quite drastically. 

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
Current through resistor C (39 ohms)
0.4A
0.37A
Voltage across resistor D (20 ohms)
17.46V
16.7V
Total power dissipated by the circuit
25.4W
24.4W

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

There can be many reasons for this difference. Here are some of them

  • Resistor tolerances
  • Cable and connector resistance
  • Power supply accuracy
  • Meter calibration

To understand one of the above reasons, we measured the resistance values of the resistors in this circuit. Here is the comparison

Resistor Theoretical Value Practical Value
Resistor A
2 ohms
2.15 ohms
Resistor B
5 ohms
5.25 ohms
Resistor C
39 ohms
39.2 ohms
Resistor D
20 ohms
20.3 ohms

Just the difference in the resistor values will change the total resistance, which will affect the current and all other values in the circuit. This is good information because it helps us understand that the components we choose may not behave exactly as expected, but will be close to our theoretical calculations.

If you used a different method of solving this circuit or have other reasons for the difference in the theory vs practical results, please put 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.