Home Physics You Cannot Give It Away

You Cannot Give It Away

You Cannot Give It Away


A central precept of Physics Boards relating to homework assistance is to not present options on demand however to information college students alongside a path to the reply.  The rationale behind this precept is articulated within the acquainted saying, “For those who give a hungry man a fish, you feed him for a day; if you happen to train him fish, you feed him for a lifetime.”  That stated, I’ll quote one other acquainted saying, “You possibly can lead a horse to water, however you possibly can’t make him drink.”  Then I’ll mix the 2 into “You possibly can train a hungry man fish and lead him to the water, however you possibly can’t make him fish.”

This mélange epitomizes a conclusion I reached after a long time of instructing minds, some hungry some not, suppose. How I reached this conclusion and the way I ultimately got here to phrases with it are the topic of this text.

The seeds

Once I started graduate college, my duties included serving to with grading hourly exams in massive courses (150-200 college students).  Right here is the examination query that began all of it.

An electron of cost ##-e## enters with velocity ##v## a area of uniform magnetic area ##B## directed into the web page.  It exits at a proper angle from its authentic route (see determine). Discover the work that the magnetic drive does on the electron from entry to exit.

magnetic field diagram

(A) ##~evBdfrac{pi R}{2}##

(B) ##~-evBdfrac{pi R}{2}##

(C) ##~evBsqrt{2}R##

(D) ##~##  Zero.


Surprisingly few college students, perhaps a handful or two, gave the right reply (D).  Most college students selected (A) or (B) persistently with the dreaded generalization “work is drive occasions distance.” I used to be astonished as a result of the professor accountable for the course had a sterling instructing repute. Absolutely, he will need to have taught it proper.

A number of years later, as a postdoc, I volunteered to team-teach a course on Fashionable Physics with a view to achieve demonstrable instructing expertise earlier than making use of for a “actual” job.  The course was cut up into two 30-student sections with a typical syllabus set by my teammate professor. The small print of implementing the syllabus for my part have been left as much as me and included authoring the hourly assessments.

Shortly earlier than the winter vacation break, I gave a scheduled brief hourly take a look at.  My directions have been “Choose any two (emphasis within the authentic) of the next three statements, reply “True” or “False” and  justify your reply.”  To verify they acquired it, I learn aloud the directions earlier than handing out the questions.  The primary assertion was associated to the Bohr mannequin and the second to Compton scattering.

The third assertion was “It’s enjoyable to experience on a one-horse open sleigh.”  It was my vacation reward to the category and I awarded full credit score to all solutions and justifications.  Nonetheless, about 1/3 of the scholars declined my provide and labored on the primary two questions.  One in all them advised me that she answered the primary two questions “simply in case” as a result of she didn’t consider I meant it.  I noticed a component of mistrust stemming, maybe, from an ingrained notion that college students and instructors are adversaries.  I used to be chagrined with the tip outcome and by no means contemplated “presents” of this type once more.

The germination of an concept

Quick ahead a decade. In my “actual” job as a college assistant professor, my flip got here to show calculus-based introductory E&M to a big class.  After we acquired to “Movement of Charged Particles in Magnetic Fields,” I took additional care to level out that the Lorentz drive is all the time perpendicular to the rate and, subsequently, to the trail, that it does no work and that kinetic power is conserved.  For good measure, I confirmed how the work-energy theorem suits in. Lastly, I concluded with “and if somebody asks you to seek out the work performed by the magnetic drive on the charged particle, don’t be fooled.  The one right reply is zero.”  Because the reader might need guessed, I had determined at the moment to be the “somebody”  and put the query on the ultimate examination.

Upon grading the finals, I used to be distressed to see that solely a few quarter of the solutions have been right.  I went to see David, a veteran of the ditch wars in opposition to ignorance, who was my unofficial mentor. I defined what occurred and vented my frustration: however I advised them!  He stated, “Telling them is meaningless to a number of college students.” Then he associated a narrative of his personal.  After a dismal efficiency of his college students on a homework downside in his Intermediate Mechanics class, he introduced that he would put the identical downside on the ultimate. Effectively, you guessed it, solely a handful of his college students studied the issue and improved their efficiency. He concluded his story by saying, “Even if you happen to inform them, there’ll all the time be some who gained’t consider you.”  Flashback to the coed who rejected my vacation reward.

Nonetheless, I stubbornly discounted David’s recommendation.  When “Movement of Charged Particles in Magnetic Fields” got here across the subsequent yr, I used to be ready.  I began with the presentation from the yr earlier than.  Nonetheless, since that alone didn’t work, I labored out the query on the board and defined why the reply is (D).  Then I overtly advised them. I stated, “I defined all this to final yr’s class, however solely 1 / 4 acquired it proper on the ultimate.  Don’t be like them.  For those who see this once more, do not forget that uniform magnetic fields do zero work.”  I keep in mind my voice wavering as a result of a part of me was questioning whether or not I’m freely giving an excessive amount of.

Judgment day got here and went with minimal enchancment. The fraction of right solutions rose from one-quarter to one-third.  I went again to David with my second however I advised them account.  He listened silently with a “and I advised you” smirk on his face.

For those who can’t beat them, be part of them

Chastened by the expertise, I turned satisfied that telling them is critical to show however not attain college students.  Main them to the fountain of information just isn’t a assure that they might drink.  That was my “aha” second.  Since it’s tough to offer away even one query, I reasoned, why not give all of them away? Thus, the booklet got here into being.

The booklet

The booklet was a compendium of about 120 homework-style however non-textbook issues from materials coated all through the course. I printed it on the net for all to see.  On the primary day of courses, I introduced that every of the three hourly exams plus the ultimate will include randomly chosen issues from the booklet.  No methods, no gimmicks, no guessing, no hidden traps.  All issues had numerical variables with numerical solutions in order that college students may test and confirm their work. Nonetheless, questions on exams will seem with the numbers eliminated.  College students must derive the solutions in symbolic type and present their derivations.  The booklet sections that may be honest recreation for every examination and my workplace hours for offering assist have been included.  The Appendix exhibits two pattern issues from sections “Coulomb’s Regulation” and “Particles, Magnetic Fields & Currents”.

How did it work?

In idea

Ideally, a scholar will try all the issues acceptable to a specific examination earlier than the occasion. The makes an attempt ought to be concurrent with the associated homework to permit enough time for asking questions.  I additionally inspired the formation of research teams during which the scholars may work collectively and assist one another.  I figured that perhaps the horses that don’t need to drink may study from people who do.  Additionally, by eradicating the numbers within the examination model, I hoped that college students would summary and keep in mind a strategic and conceptual method for every downside and convey that to the examination.

I used to be not nervous that I gave an excessive amount of away for 2 causes: (a) David taught me that it’s not attainable to offer an excessive amount of away; (b) in my thoughts, any scholar, who is ready to reproduce the algebraic options to fastidiously crafted issues, has completed the targets of the course. I couldn’t count on extra.

In observe

First the dangerous information.  Pupil site visitors in my workplace was the identical relative to the pre-booklet days. Solely the main target of the visits modified from serving to with tough homework issues to serving to with booklet issues.  Some college students waited till the final second after which crammed.  Others performed the lottery and studied solely the issues they guessed I’d placed on the take a look at.  They didn’t consider me that the choice can be random.  Some felt that since they “knew” what will probably be on the examination, they may wing it with out understanding the issues.  In brief,  the introduction of the booklet didn’t noticeably affect scholar habits or their efficiency on exams.  One may suppose that every one of them would leap on the alternative of realizing what can be on the examination. Not so.  Motivated horses drank, unmotivated ones didn’t.

Now for the excellent news.  The booklet turned out to be a win-win state of affairs. For the scholars, it mitigated the concern and psychological paralysis that afflict a number of college students earlier than and through exams. An oft-heard lament was, “I assumed I understood the fabric, I did all of the homework, however once I got here to the examination I freaked out.” With the booklet, the anxiety-producing unknowns, e.g. stage of issue, the character of the questions, the place one ought to pay attention one’s efforts, whether or not one has enough preparation, and many others. turned knowns.  The booklet positioned the duty of the coed’s efficiency squarely upon themselves to the place it belongs.

Because of this, the booklet’s profit to me was peace of thoughts. It eliminated the reasons that college students use to shift the duty for his or her poor efficiency away from themselves: “The examination issues have been nothing just like the homework”; “we didn’t cowl this at school”; “I didn’t perceive this once we coated it at school”; “the examination was too tough”; “the examination was too laborious”; “you didn’t train us resolve this type of downside” and so forth.

Nonetheless, the actual winners have been the motivated college students (about 20%) who took the booklet to coronary heart.  For them, it labored as I supposed.  They handled the booklet issues as self-assigned homework. They got here to workplace hours with questions on a weekly foundation usually as groups working collectively.

The booklet additionally labored wonders with college students who did poorly however cared sufficient to return and ask me how they may enhance their efficiency. Most of them have been last-minute crammers with poor time-management abilities. For them, I constructed timetables to prepare what to finish by what date and left it as much as them. The subsequent important group consisted of scholars with shaky math or physics problem-solving abilities. For them, I added a second set of timetables with to-learn lists.

No matter potential, all motivated college students realized I didn’t design exams to reveal their ignorance however to consolidate their studying. That was a giant win for them and me.

Crafting the booklet

The booklet issues have not more than two sequential steps within the derivation and aren’t multipart issues.  Every query brings collectively ideas or abilities that college students ought to have acquired in another a part of the course or course stipulations. As soon as solved numerically, the development of the questions makes the transition from numerical to symbolic type clear.  Moreover, the questions don’t require greater than two sequential steps and the answer methods are one-liners.

For instance, questions 1.6 and 1.7, which can’t seem collectively on the identical examination, mix electrostatics and free physique diagrams. The technique in each is “Draw an FBD for the highest (or backside) bead” and say that the online drive on the chosen bead is zero.”  The trick (if there’s one) is to comprehend that, though the highest bead is free to maneuver, the string has to help the burden of each beads.

In query 6.5 the technique is “Categorical the magnitude of every wire’s contribution to the B-field when it comes to the radius of the circle and the suitable trig capabilities and set the 2 magnitudes equal.”  The query brings collectively the magnetic area of an infinite wire, superposition, and the right-hand rule. It additionally requires one to recollect the identification ##sin(apm b)=sin acos bpmcos a sin b.##


The customary understanding between teacher and college students is, “I’m going to show you after which I’ll study you to find out what you’ve got discovered and what you are able to do.”  That’s OK in precept, nonetheless, there’s usually a spot separating the tip of instructing from the start of studying. When college students carry out poorly, instructors are inclined to blame the scholars for not studying and college students are inclined to blame the instructors for not instructing.  Nonetheless, each side declare to have performed their finest.

This hole turned painfully obvious to me with the electron-in-a-magnetic area query which I now remorse asking.  It was a repeated measurement of what 2/3 (at finest) of the scholars can’t do, not what they can do.   There isn’t any data to find out what college students can’t do, instructors already comprehend it.  The booklet shrunk the hole between instructing and studying.  It outlined a boundary between the 2 with a transparent message: “Here’s what I count on you to have the ability to do. Let’s each see how effectively you are able to do it.  If there’s something that you simply can’t perceive or do, ask me earlier than you’re examined.”  To fish or to not fish, that’s the query.


In multipart booklet questions, corresponding to those under, every half is standalone and doesn’t require fixing one other half first. So far as the random quantity generator is worried, every numbered half is a separate query, however questions sharing a descriptive assertion don’t seem collectively on the identical examination, e.g. 1.6 or 1.7 however by no means 1.6 and 1.7.  Variables on the examination would not have numerical values; their symbols are left in place for college kids to make use of as given portions.

bead on string physics problem diagram

current in wire diagram problem



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