@pkaps01 correct me if Iām wrong, but UWorld gives the Lorentz force as F = qvBsin(theta), which is given in the image in this card.
Weird. That photo I posted above is from the UWorld Q bank explanations. That definition in your pic (just the magnetic force) also seems to contradict the definition we have in the text of the card: {{c1::Lorentz force::ā¦ force}} is the sum of the {{c2::electrostatic }} and {{c2::magnetic }} forces acting on a body.
Another relevant card in the deck:
It may just be a term difference (albeit annoying).
Iāve seen Lorentz used both as qvB as well as for B and E, though Iāve also seen the combined version referred to as the ācombined Lorentzā though I canāt recall where.
FWIW Kaplan says that it is both magnetic and electric, though does not specify an equation.
I will add, and itās just anecdotal, Iāve never see the combined equation required where it wasnāt also given.
Do you think it makes sense to include in the extra at least? My feeling is that if thereās no electric field present its intuitive to substitute 0 but if there is an electric field present (and on the off chance the equation isnāt provided) you are unlikely to know what to do with it to find the Lorentz Force if you only know f = qvbsin(theta). To be honest Iāve only ever known/seen the equation as including both in school. I should also add vector notation above the terms to make it clear the magnetic force is a vector cross product - directly necessary for answering this UWorld Question:
Youāre also right. UWorld seems to treat this concept in terms of an āelectric Lorentz Forceā and āmagnetic Lorentz Forceā
But the total Lorentz Force is both.
Well:
- 1: the card is not about the equation, really.
- 2: I think, as a purely first-order consideration, there is a strong argument against including two contradicting equations in the same note, much less in a note that is not immediately about the equation at all.
Weāre likely to run into the same trap weāve discussed previously which is chasing our tail trying to convey a bunch of nuance that the card didnāt ask about, and arguably isnāt likely to convey well.
Iām good with whatever you think. I guess my opinion on this is I would rather have the whole equation than an image with part of the equation (I agree having both is confusing and would rather delete the image). I just feel like having the form of the equation with both electric field and magnetic field included makes sense if we are going to include an equation at all when the card says {{c1::Lorentz force::ā¦ force}} is the sum of the {{c2::electrostatic }} and {{c2::magnetic }} forces acting on a body. All good if we disagree though.
Especially since that equation and graphic is already here:
Iām not opposed to adding something, to be clear. But what are we going to add?
Thereās not evidently a consensus on what the equation terminology is. Are we just going to insert a new equation, not otherwise mentioned in the deck, into a single note that is not immediately about the equation? I think, if thatās the solution proposed, that the idea leaves some things to be desired (particularly for an equation that is not referenced directly in a primary textbook).
Then, how to resolve primary source that more or less verbatim says Lorentz F = qvB?
The truth is that this would be a great candidate for its own card. Though again, we donāt have any evidence of it in a primary text and a single incidence of it in a question bank question. Iām not entirely certain that level of proof-burden rises above the question marks listed above.
Lastly, the question you shared seems to hinge entirely on direction of force production in a magnetic field. So the question stem itself does not appear to necessitate recall of said equation, which seems to be sort of included in the post-question explanation section if Iām gathering it right.
Iām not poo-pooing your points outright; Iām trying to convey what my concerns are (and trying to instill a sense of judiciousness about what rises to the level of merited inclusion).
TL; DR: equation sort of mentioned in an explanation section + not directly required to answer the question + equation not otherwise mentioned in a primary source + proposed inclusion of said equation would not only be the only mention in the deck but contradict other primary source/s and in a card thatās not immediately about the equation.
I dunno
All fair points. I guess my familiarity with the equation outside the MCAT is playing a role. I do see that UWorld is conflicting in that it says the Lorentz Force is two different things in the qbank explanation and textbook portion. Though Kaplanās definition appears in agreement with my suggestion.
I saw that the Lorentz Force was tested in one of the more recent official MCATs so was looking for a solution to this card. Especially since it seems like the primary sources arenāt offering much help so it felt like an opportunity.
Not sure what we can do here though. I donāt get how these huge companies cant maintain internal consistency in their definitions haha.
Should we even have the current image with the equation at all then? given it conflicts with the definition in the card and thereās no consensus with UWorld? Or take an approach that Iāve seen more with the step deck and list the two equations and note the discrepancy?
I for sure remember the qvB being in an AAMC thing, though itās been long enough now that I canāt recall if it was a practice QBank, or a FL, or what.
Lolol, we are in complete agreement that this is a source of frustration. Really if AAMC wanted to make their own textbooks to squeeze out the cottage market industries here that crop up around the MCAT our life would be a lot easier.
I think, in a dream world, listing the discrepancy in source would be ideal for a card that is dedicated to the equation itself. But even then, do we have evidence yet that the combined equation is testable? Thus far itās just in an accompaniment explanation; we donāt have (unless Iām missing something) evidence that itās required recall.
As for the image, the right-hand-rule is one of those things where, at least to me, it sort of famously has a million crappy images. I canāt recall having seen a single one that just floored me with its awesomeness. Iām not against replacing it, if you have a candidate you think is better-suited. I donāt think the current image is inappropriate, really, but Iām never against gussying up visuals where we can.
A couple of quick thoughts, while they occur to me:
When I was trained, the two tacit conditions for inclusion of new details/information/tags were thus:
- Is it verbatim mentioned in a primary source and we donāt have it? Okay, kind of a no-brainer in many/most cases.
- Is this information necessary to answer a question? As in, without it one cannot answer the question.
In this case, at least, Iām not sure that I see either are held up. And for sure not both.
For this question, which requires understanding magnetic force occurs at a right angle, bla bla, you donāt really need any math at all. You donāt really even need to know that there is an equation, arguably. Simple conceptual understanding that, in the conditions ascribed, a magnetic force will act at a right angle and/or familiarity with the right hand rule is enough to land the answer.
The above conditions were sort of drilled into me when I started, so Iām sharing them here as litmus tests for what gets included, what gets advocated for, and how to think about the necessary thresholds that you want to clear for proposed inclusion. I donāt think Iām going to claim that those are always the requirements 1000% of the time for everything, but for sure if those conditions are not met itās much shakier ground to stand on.
Otherwise, we sort of end up in a spot where weāre adding things that ācould be helpful.ā And that is, pointedly, not helpful. Itās a judgement-case based on a conditional and ends up being a recipe for bloat.
Now: itās time for lunchhhh
qvb does come up in the AAMC Qpacks but not specifically in reference to the Lorentz Force. Makes sense to me. Iāll just keep it in my personal notes for the card.