IP4 13 DC Circuits

Internal Resistance and Terminal Potential Difference


This applet demonstrates how terminal potential difference (as measured by the voltmeter across the terminals of the battery) changes depending on :

  1. internal resistance r
  2. external resistance R
  3. emf E
  4. when a switch is turned on and off
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Potential Divider with Thermistor Applet

The wonderful thing about GeoGebra is that you can whip up an applet from scratch within an hour just before your lesson and use it immediately to demonstrate a concept involving interdependent variables. I was motivated to do this after trying to explain a question to my IP4 students.

The RGB colours of the thermistor reflects the temperature (red being hot, bluish-purple being cold)


This was done to demonstrate the application of potential dividers involving a thermistor and a variable resistor. It can, of course, be modified very quickly to introduce other circuit components.

Videos on Series and Parallel Bulbs

These are two videos that I made on series and parallel bulbs. The second video is specially made to highlight the increase in brightness of the remaining bulbs when one or more bulbs is removed from its socket.

What students will learn in O levels is that the brightness of the bulbs will not change as the potential difference is a constant, being the emf itself.

Based on the conflict between what is taught and what is observed, students will be led to discuss the reason why.

If anyone is interested in getting the demonstration kit, do check out Funlearners.com.

Hidden Circuits Interactive

I made this interactive tool using javascript for the teaching of DC circuits for integration with SLS as part of the IP4 Physics blended learning experience in the upcoming weeks.

The intention of this interactive is for students to do a preliminary inquiry activity to exercise what they learnt about series and parallel circuits. They can be tasked to draw out what they think the circuit diagram will be like, either on Nearpod or SLS.

Students can even notice the differences in brightness under different conditions. Questions can be designed around this as well.

Previously we used to construct little boxes with wires hidden underneath. However, due to wear and tear and with Covid-19’s safe management measures, a digital version that can be accessed via the students’ mobile devices is more suitable.

Light bulb image is adapted from Good Ware from www.flaticon.com
Switch image is adapted from Those Icons from www.flaticon.com

For a direct link to this interactive, please go to: https://www.physicslens.com/wp-content/uploads/2022/04/index.html (updated link)

To obtain the zip file for upload into SLS as an interactive media object, click here.

Internal Resistance and Maximum Power Theorem

I’ve created this simulation to demonstrate the effect of an internal resistance due to a cell on the potential difference and current of an external load.

One can also vary the internal resistance and external resistance to observe the maximum power theorem. The theorem states that for a given finite internal resistance, one can obtain the maximum external power only when the resistance of the load is equal to the internal resistance of the source.