The plasma globe or plasma ball is an underutilized resource for teaching the physics of electricity. It also offers a convenient source of electric field that can be used for demonstrations and experiments. Unlike the Van de Graaff generator, the plasma globe does not shock you and is essentially silent. Other authors have written up some of these activities, but the full potential of the plasma globe is generally not taken advantage of by most teachers. I hope that this article can bring more awareness to how this ubiquitous piece of novelty lighting can be an essential physics teaching apparatus.
REFERENCES
1.
This article comes with an online video abstract at TPT Online, https://doi.org/10.1119/1.5018702 E-PHTEAH-56-031801.
2.
I perform many of the demonstrations in my AAPT Films videos: “
Top 10 Ways to See the Electric Field Parts 1 and 2
,” http://www.youtube.com/watch?v=Y6YdC2UoDYY and http://www.youtube.com/watch?v=bOLd2KVK-Mo.3.
Nicholas R.
Guilbert
, “Deconstructing a plasma globe
,” Phys. Teach.
37
, 11
(Jan.
1999
)4.
Wheijen
Chang
, “Integrating electrostatics with demonstrations and interactive teaching
,” Am. J. Phys.
79
, 226
(Feb.
2011
).5.
This is known as the Thomson cascade; see Nicholas Guilbert
, “Shedding some light on fluorescent bulbs
,” Phys. Teach.
34
, 20
(Jan.
1996
).6.
You may wonder why the electric field doesn’t just ionize the air around the globe. The E-field is not high enough to ionize air at 1 Atm, unless a conductor is employed to focus it. This can be accomplished by simply putting a penny on top of the plasma globe and touching it with your finger. This will generate a small (semi-painless) spark and is a lot of fun.
7.
You probably have one of these tubes above your head in your classroom; ask a custodian to help you borrow it. Otherwise, the very long ones can be found at hardware stores, which I recommend.
© 2018 American Association of Physics Teachers.
2018
American Association of Physics Teachers
AAPT members receive access to The Physics Teacher and the American Journal of Physics as a member benefit. To learn more about this member benefit and becoming an AAPT member, visit the Joining AAPT page.