Let me just say at the outset that this post is Reason I'm a Terrible Person #417.
I was scoping out the YouTubes in search of a nice video lesson on the photoelectric effect. Demonstrating the effect can be troublesome and finicky. So why not enjoy the fruits of someone else's labor?
I watched through Adam Micolich's lesson (below) and... found it wanting. Wanting to be used as a lesson in skepticism and critical thinking!
The story/script is nicely straightforward:
1. A negatively charged electroscope is discharged via exposure to ultraviolet light.
2. The UV light is causing the discharge: a glass plate blocks the UV and prevents the discharge.
3. The UV liberates electrons: a positively charged electroscope is not discharged by UV light.
Let's see how it goes. (The actual photoelectric demo begins at about 2:50.)
Each segment seemed to go according to plan and proved the aspect being investigated. The content as spoken is spot-on correct.
And I have no reason to suspect shenanigans. But in my judgment, the demonstration is flawed to the point it would be fraudulent if done intentionally.
Consider it a PhyzMaster Challenge: Can you find the flaws I found?
I offer this challenge in good faith as an exercise in physics-based critical thinking. These principles are ostensibly valued by Common Core, NGSS, and the reimagined AP Physics courses. I mean no disrespect to Mr. Micolich. He was good enough to produce the video lesson; I—someone who didn't bother to create a video lesson of the photoelectric effect—spent a Saturday night finding fault with it. So who is more deserving of harsh judgment? (That was rhetorical.)
Hints and specific allegations in the comments. I might remove these later if I assign a skeptical critique to my students.