Faraday Cage: AM vs. FM

To demonstrate the fact that electric fields (unlike gravitational fields) can be shielded, I have taken to showing the effects of a Faraday cage on radio signals. (I wonder how many more years I'll be able to perform this demonstration this way.) I use a transistor radio as my "field detector" and a metal colander and a metal splatter screen as my blockers.

In serendipitous monkeying around, I noticed that FM signals "behave" better for this demonstration than AM signals do.

The FM seems impervious to being placed on the screen or in the colander. But when encapsulated, it virtually drops to nothing.

The AM signal, on the other hand, is sensitive to being placed in the screen or in the colander. But the signal remains intelligible even when the radio is fully encapsulated.

Take a look.

Faraday Cage AM FM

ExploratoRio 2014: The 20th Anniversary Begins

Today the exhibit recipes were posted. I plan to adopt them out prior to the Presidents' Week break.

ExploratoRio 2014 Exhibit Recipes Posted



For more on ExploratoRio, see
ExploratoRio Resources.

Evidence of ball lightning published in PRL

Physical Review Letters has published the work of Chinese scientists who appear to have recorded an instance of ball lightning.

Ball Lightning
Chinese scientists have recorded the rare phenomenon in nature for the first time

Here's a quick review of ball lightning.

And the video (with spectrometer image).

First recorded scientific video of Ball Lightning

Van de Graaff Hair 2014: first draft

No post-processing or culling. These were the pics as taken.

Balanced Balloons - a new Figuring Physics

I am delighted to have developed some "Figuring Physics" ideas for The Physics Teacher columnist, Paul Hewitt over the years.

If you want a treasure-trove of Hewitt's "Figuring Physics" (a.k.a. "Next-Time Questions"), you're in luck.

Hewitt's Next-Time Questions at Arbor Scientific

We're in the midst of our study of electrostatics. Usually this brings torrents of rain to Northern California. This year's drought seems to be impervious to my machinations.

In any case, this little puzzle came to mind. It was preceded by the developments of Balancing Charges 1 and Balancing Charges 2 PhyzJobs. But I turned the concept into a standalone puzzle.

We begin with two helium-filled balloons that, when oppositely charged, are exactly balanced. They are attached to a massless bar that has a frictionless hinge at its midpoint.

I'll post the answer in the comments next week. It's a fun one to think through. Maybe it will make the cut for next year's round of "Figuring Physics."

Dan Burns updated his Science on The Simpsons page

From Dan:

"Hello Science on the Simpsons fans, I have added 13 more clips to the website. I included more biology related ones so share it with your life-science colleagues. Don't worry, there are some new physics ones like "Faster than Sound" and "Black Hole 1 and 2". The new clips start with "Acid Rain" in the right column:

Science on The Simpsons

Remember these are for educational purposes only.

Dan Burns
Los Gatos High School"

Go take a look. But be warned, you may find yourself binge-viewing the clips!

The new adventures of old Star Trek

Did you know about this and not tell me?

Star Trek Continues E01 "Pilgrim of Eternity"



Jimmy Doohan's son playing Scotty? Marina Sirtis as the ship's computer? Nichelle Nichols guest appearance?

It's certainly not J.J. Abrams' Star Trek. And I count that as a plus, as I've seen about as much emotion splashing out of Zachary Quinto's Spock as I care to.

This holds true to The Original Series' aesthetics and sensibilities, for better or worse. And I'll apologize right now for the hour you're about to lose watching this. If you're a TOS fan, you won't regret it.

Hewitt Drew It! screencast directory update

Paul Hewitt continues to produce screencasts. And I think I've final caught up with him on my simple, home-made directory.

Screencasts for Atomic and Nuclear Physics and Relativity have not yet been released. But there are over 120 Conceptual Physics screencasts out there right now!

Hewitt Drew It! Screencast Directory

Lightning shot at 11,000 FPS

PetaPixel has an article about some incredible high-speed lightning video. And they link to the goods!

Incredible High Speed Video of Lightning Captured at 11,000 Frames Per Second

Here's the clip posted to YouTube.

Incredible Slow Motion Lightning Strike! (1 sec. = 3 min!)



I had never seen the "sparkling" high in the clouds as the stroke develops. So much randomness before a channel is established. The things you can see with high-speed video!

Figuring Physics: EQUIVALENT RESISTANCE

This month's The Physics Teacher (TPT) includes my most recent contribution to Paul Hewitt's "Figuring Physics" panel. Figuring Physics questions are not easy to develop, and many good questions are not good Figuring Physics questions.

Here's a link to the page that will give you access to downloading a PDF of the panel.

January 2014 Figuring Physics

Apparently TPT now waits a month before revealing the answer panel. So you're on your own for now.