magnetic fields - 2026 ACF Regionals

Question

The topology of these constructs is given by their helicity, which is the sum of their writhe and twist. For 10 points each:

[10e] Name these vector fields whose lines can be visualized using iron filings and are drawn from the north to south pole.

ANSWER: magnetic fields [accept magnetic field lines; or B-field]

[10m] For a particle in a non-uniform magnetic field, they experience a component of this quantity proportional to the gradient of B. For electrons in a uniform electric field, this quantity equals mobility times electric field.

ANSWER: drift velocity [prompt on drift; prompt on velocity; prompt on u]

[10h] Moving particles in a magnetic field also experience a drift velocity term named for and proportional to this quantity. In MHD, magnetic fields with a non-zero value of this quantity experience magnetic tension equal to this quantity times B-squared over permeability of free space.

ANSWER: curvature [accept curvature drift; prompt on kappa; reject “radius of curvature”]

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Summary


California (North)	Main Site	Y	3	13.33	100%	33%	0%
California (South)	Main Site	Y	4	7.50	75%	0%	0%
Canada	Main Site	Y	7	8.57	86%	0%	0%
Florida	Main Site	Y	1	20.00	100%	100%	0%
Great Lakes	Main Site	Y	5	14.00	100%	40%	0%
Lower Mid-Atlantic	Main Site	Y	7	10.00	100%	0%	0%
Midwest	Main Site	Y	5	8.00	80%	0%	0%
Northeast	Main Site	Y	3	13.33	100%	33%	0%
Overflow	Main Site	Y	3	10.00	100%	0%	0%
South Central	Main Site	Y	1	0.00	0%	0%	0%
Southeast	Main Site	Y	5	10.00	100%	0%	0%
UK	Main Site	Y	10	11.00	100%	10%	0%
Upper Mid-Atlantic	Main Site	Y	7	11.43	100%	14%	0%
Upstate NY	Main Site	Y	2	10.00	50%	50%	0%

Data


Stanford A	Berkeley A	10	0	10
UC Irvine	UC Santa Barbara	10	0	10
UCLA A	Arizona State	10	0	10
UCLA B	UCSD A	10	0	10
UCSD B	UCSD C	0	0	0
Toronto B	Carleton University	10	0	10
Guelph	Waterloo B	10	0	10
McGill B	Western C	10	0	10
Brock	McMaster B	0	0	0
Waterloo A	Ottawa	10	0	10
Queen's	Simon Fraser	10	0	10
UBC A	Western A	10	0	10
Central Florida A	Florida B	10	10	20
Michigan B	Michigan A	10	0	10
Ohio State A	Michigan C	10	10	20
Ohio State B	CWRU A	10	10	20
CWRU B	Ohio State C	10	0	10
Pittsburgh	Michigan State	10	0	10
Duke	NC State A	10	0	10
Virginia Tech B	James Madison A	10	0	10
Virginia	NC State B	10	0	10
William and Mary	North Carolina A	10	0	10
South Carolina A	Wake Forest	10	0	10
North Carolina C	South Carolina B	10	0	10
Virginia Tech A	Liberty B	10	0	10
Berkeley B	Berkeley D	10	10	20
Illinois B	Illinois A	10	0	10
Indiana A	Purdue B	10	0	10
Chicago E	Northwestern C	0	0	0
Notre Dame B	Chicago D	10	0	10
Purdue A	Indiana C	10	0	10
Washington A	Claremont	10	0	10
Minnesota A	Missouri A	10	0	10
Georgia Tech A	Washington B	10	0	10
Murray State A	Texas A	0	0	0
Harvard A	Brandeis B	10	10	20
Harvard B	Bowdoin A	10	0	10
MIT	Brown	10	0	10
Bruin	Alabama A	10	0	10
Louisville B	Alabama B	10	0	10
Georgia Tech C	Kentucky	10	0	10
Mississipi State	Louisville A	10	0	10
Georgia Tech B	WashU B	10	0	10
Birmingham	Imperial B	10	0	10
Edinburgh A	Cambridge A	10	0	10
UCL	Edinburgh B	10	0	10
Imperial A	Bristol	10	10	20
Imperial C	City St. George's	10	0	10
Durham	LSE	10	0	10
Warwick A	Manchester	10	0	10
Montpellier	Southampton A	10	0	10
Oxford A	Cambridge B	10	0	10
Oxford B	Cambridge C	10	0	10
Columbia A	Georgetown	10	0	10
John Jay	Columbia C	10	0	10
Johns Hopkins A	Maryland B	10	0	10
Rutgers B	NYU A	10	0	10
NYU B	Maryland C	10	0	10
Columbia B	NYU C	10	0	10
Rutgers A	Swarthmore	10	10	20
Cornell A	Cornell C	10	10	20
Penn State	RIT	0	0	0
Stanford B	Berkeley C	10	0	10