charge - 2024 ACF Winter at Online

Question

Robert Millikan’s oil drop experiment measured the “elementary” value of this quantity, which is the smallest amount of this quantity that can exist on its own. For 10 points each:

[10e] Name this quantity, which is negative 1.602 times 10-to-the-minus-19 coulombs for an electron.

ANSWER: charge [accept elementary charge; prompt on q]

[10m] Conservation of charge is expressed as [read slowly] “the time derivative of charge density plus [this operation] applied to current density equals zero.” Gauss’s law states that this operation applied to the B-field equals zero, implying magnetic monopoles do not exist.

ANSWER: divergence [accept div or del dot or nabla dot; reject “del” or “dot” alone]

[10h] Per Noether’s (“NURR-tuh’s”) theorem, conservation of charge is a consequence of one of these conditions being invariant with respect to a transformation. Another one of these conditions sets the divergence of the vector potential to zero.

ANSWER: gauge [accept gauge invariance or Coulomb gauge]

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Summary


2024 ACF Winter at UC Berkeley	2024-11-16	Y	3	26.67	100%	100%	67%
2024 ACF Winter at Lehigh	2024-11-16	Y	7	18.57	100%	57%	29%
2024 ACF Winter at Northwestern	2024-11-16	Y	7	12.86	71%	43%	14%
2024 ACF Winter at Ohio State	2024-11-16	Y	6	16.67	100%	50%	17%
2024 ACF Winter at Online	2024-11-16	Y	8	11.25	88%	25%	0%
2024 ACF Winter at Central Florida	2024-11-16	Y	5	16.00	80%	60%	20%
2024 ACF Winter at Oxford	2024-11-16	Y	10	16.00	100%	40%	20%
2024 ACF Winter at Brandeis	2024-11-16	Y	10	12.00	90%	30%	0%

Data


Arkansas	Colorado College	10	0	10
McGill E	Vassar B	10	0	10
Texas B	Mississippi State	10	10	20
WUSTL A	NYU A	10	0	10
Texas D	Oregon State	0	0	0
Missouri	Texas A	10	0	10
Vassar A	Ole Miss	10	10	20
Iowa	Central Oklahoma	10	0	10