AC Power with Half-Wave Rectification

As a means of visualising what happens to the potential difference, current and power dissipated in an alternating current circuit with half-wave rectification, I have created the interactive applet with all 3 graphs next to each other.

It should be easy for students to see that with half-wave rectification, the power dissipated is half that of a normal a.c. supply with the same peak p.d. and current.

Simulation on the effect of vaccination on the spread of Covid-19

My ex-colleague Lawrence did a simplified simulation on how vaccination can work to slow down the spread of Covid-19. It shows a clear correlation between rate of transmission and percentage vaccinated. Of course, experts recommend 80% vaccination rate but every bit counts as you can see from the simulation. I will be sure to receive mine when we get our turn.

It could also be useful for educating the public on the continued need for social distancing/masks despite having a sizeable population being vaccinated.

(Note: p = probability of spread upon contact, and you can use the dropdown menu to select different modes of safe management measures)

Electric Potential between Two Point Charges

In preparing for blended learning lessons for my JC2 students, I tweaked the Gravitational Potential applet made last year for a similar display of the electric potential between two point charges. This is a testament to the similarities between the two concepts as well as the ease of adapting a GeoGebra applet for education.

We can scaffold students’ learning using this interactive applet by asking questions such as:

  1. By observing the electric potential graph, are you able to find a point when the net field / force acting on a test charge is zero? What are the necessary conditions?
  2. The slope of the sum of the electric potentials is analogous to that of a physical slope where a ball will roll downhill in the same way that a positive test charge will accelerate based on the potential gradient. However, this analogy will work differently for a test charge that is negative. Why?
  3. Given that $E = -\dfrac{dV}{dx}$, where x is the distance from the point charge, is the direction of the E-field vector consistent with the negative of slope?

To paste this applet into SLS, use the following embed code. In SLS, create a new component within an Activity within a Lesson using the “+” button. Choose Text/Media and select the button that shows “</>” or reads Embed Website/App”. Copy and paste the following codes to the box.

<iframe scrolling="no" title="Electric Potential of Two Point Charges" src="" width="640px" height="480px" style="border:0px;"> </iframe>

By embedding the gravitational potential distance graph for two masses, a comparison can be made between the two. This will help students draw connections between the two concepts based on the fact that the forces both follow an inverse-square law.

This is the embed code for the applet on gravitational potential.
<iframe scrolling="no" title="Gravitational Potential between Two Planets" src="" width="638px" height="478px" style="border:0px;"> </iframe>

Root-mean-square Currents

The concept of root-mean-square values for Alternating Currents is challenging if students are to relate the I-t graph with the Irms value directly.

They have to be brought through the 3 steps before arriving at the Irms value. This interactive applet allows them to go through step by step and compare several graphs at one time to see the relationship.

Through the interaction, students might be asked to observe that the Irms value is never higher than the peak Io.

For a complete sinusoidal current:

For a diode-rectified current:

In comparing the Irms of both currents, students can be asked to consider why the ratio of the values is not 2:1 or any other value, from energy considerations.

Worked on this earlier as I am the lead lecturer for this JC2 topic and am trying to integrate useful elements of blended learning. Do let me know in the comments if you have ideas or feedback that you would like to share.