RH Grip Rule

Originally uploaded by coach_robbo

I’m slowly adding to the concept maps to my Flickr page to include some of the things discussed in class. Visual thinking tools have been shown to improve understanding of complex topics.
Let me know if there are any requests.

photoelectric effect current and voltage
Originally uploaded by coach_robbo

Here is the photocurrent vs voltage graph we concentrated on for a bit today. Add this to the energy vs frequency graph and you have the photoelectric effect pretty much covered. If you follow through the flow chart in the earlier post “Photoelectric effect starter” you should see consistency with both graphs. I cannot recommend enough reinforcing this with the PhET photoelectric simulation. It’s available for download so you can run it offline if preferred. (You will need to install Java but there are instructions on the site.) Do it. If you invest 20 focused minutes (not “Oh, I’ll just listen to this and watch that at the same time” – focused minutes) it will pay you back.

photoelectric effect energy vs freq
Originally uploaded by coach_robbo

Listen to some terms and definitions associated with the photoelectric cell and the photoelectric effect (along with special comments). You simply have to know what these things mean. See the “audio bites” if you prefer a more polished version. The standard energy vs frequency graph you would expect to see goes with the audio of terms and definitions and has points of interest labeled.

The photoelectric effect is one of the more trippy spin outs that nature can throw you IMHO. I mean if you think about it, it doesn’t make much sense. Well this is where the simulations can really help. The very best one is the Photoelectric Interactive Solution (PhET) from the University of Boulder (we love those guys!) It shows the electrons being ejected from the photocathode and moving from one plate to the other. This visual is usually very helpful in developing understanding of the principle and the photoelectric cell. Current vs intensity, current vs voltage and electron energy vs frequency can also be viewed. Grab the virtual experiment instructions from here and see how much you can work through.
Walter Fendt has an applet offering similar features but nowhere near as “attractive” with it’s presentation. Repetition with variety is the key. We will play some real equipment next time we meet in the laboratory to take a closer look at the photoelectric effect.

Light is predominantly thought of as a wave these days but this was not always the case. Our old friend Isaac Newton put his significant scientific weight behind the particle (or corpuscular) explanation for much of light’s behaviour. It was up to guys like Young, Huygens and Fresnel to challenge the old views which was published successfully by Young in the very early 1800’s. The double slit interference experiment that underpinned the “light as a wave” model is often referred to as Young’s double slit experiment.
There is a nicely done, full colour online simulation of the double slit interference experiment here that is well worth exploring. The width of the slits, slit to screen distance and frequency of light are all adjustable and the representation of the wave from each slit along with their superposition is extremely helpful for an understanding of path difference. Quantitative data is available if desired. Walter Fendt treats it in a more simplified way here.
If that is a bit much or a refresher is required review your knowledge of waves at the ScienceJoyWagon. Some simulations require a membership but the ones available for free viewing will still prove useful.
Walter Fendt has a brilliant simulation of reflection and refraction combining the ray model with Huygens’ wave front principle. Highly recommended

Seth’s Blog: Winning on the uphills

Interesting business lesson learned on a bicycle: it’s very difficult to improve your performance on the downhills.

Applies to most things really.

I am not on campus Tuesday but forge ahead we must.
Problem Sets 13A and 13B should be attempted by now. If not that is the first thing to be attended to. Without a fundamental understanding of sound waves and what they do the rest will be a struggle.
Next step is to read up on reflection and resonance of sound waves on strings/wires. This is on p310 – 314 in your text and you should already have the class notes (get them here). Pay close attention to Fig 13.23 (p314) and the difference between terms harmonic and overtone. This can be confusing but we can (hopefully) clarify this next lesson.
The PhET simulation “Waves on a string” is very useful to visualise the concepts and the sound section of Hyperphysics has further explanations, diagrams and background information.

This activity is a great demonstration for electromagnetic induction and Lenz’ law. Just a regular aluminium egg ring on each “arm” of the “dissectible transformer”.

Why does the egg ring get launched off the top?

Why doesn’t the egg ring get launched off the top this time? It also gets quite hot (which is why you touch it carefully before removing it!) Can you explain why that happens?

We shot this video in the lab last Wednesday. If you roll your mouse over the play head as it’s moving then click on the plus sign you can add comments, tags, ask questions or explain what’s happening. They correspond to Activity 1 of the “Electrical Power Activities”.

Electromagnetic induction with permanent magnet and bobbin from dissectible transformer

Electromagnetic induction with both bobbins from dissectible transformer – no iron core

Electromagnetic induction with both bobbins from dissectible transformer - 

with iron core

I have updated the class notes for “Power Transmission” and posted them on the Unit 4 Page. All the page numbers should now match the new text, let me know if there are any errors.
There is a unit guide available here with a breakdown of topics, reading, key examples and diagrams and practice questions. It will continue to grow and evolve so it may be an idea to bookmark it.