Challenge Circuit 5

Capacitor Charging Circuit

Solution and Practical Results

In this post, I’ll show one of the ways of solving Challenge Circuit 5: Capacitor Charging Circuit and connect the circuit to get practical results. It’s also much easier to understand capacitor charging with an analog meter.

Here is the circuit from Challenge Circuit 5

Challenge Circuit 5 details


The given value were:

  • C = 1000 uF
  • R = 4.7k ohms
  • Supply voltage = 12V

Capacitors charge when DC voltage is applied across them. By connecting a resistor in series with a capacitor we can control the amount of current that goes through and hence the time it takes to charge it.

The Challenge was to find

  • Time constant
  • Full charge time
  • Expected voltage across the fully charged capacitor

Theory Solution

Here is one of the ways of solving the circuit above. 


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. In this case, the practical results were quite similar to the theoretical values.

Value Theory result Practical result
Full Charge Time
23.5 s
23.44 s
Expected Voltage across fully charged capacitor
12 V
11.68 V

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

Unlike our previous challenge circuits, the practical and theoretical values were quite close, but there was still some difference. Here are some of the factors that could be affecting the results in this circuit

  • Tolerance of the resistor
  • Tolerance of the capacitor
  • Power supply accuracy
  • Meter calibration
  • Manual timer

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.

Picture of 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.