GAMSAT Physics Crash Course #3 | Radiation | S3 For NSBs

[@PriyaGupta-ff3pt]

Hi Jesse, thanks for another wonderful vid! I am extremely confused with the first practice question despite having watched it a few times! (How) does how you solved it take into account that the daughter nucleus starts on zero and so for the first however long will have an almost negligible mass/amount? When I look at your working it seems to me like a mixed sample with equal starting amounts of X and daughter and going from there, with each independently decaying, as opposed to the very linked situation of one's decay allowing the other to start from scratch and with the daughter getting progressively more added from X decaying as well as less from itself decaying.. would you be able to clarify a bit how this works? also if possible, what the working for the potential question of starting with equal amounts of X and daughter would look like (because like I said, I would guess that you would solve that by doing what you did here). sorry if it wasn't worded properly! Thanks again :)

[@jesseosbourne]

Hey Priya! Another solid question. You know, I think when I wrote this questions, I was intending it to be one sample of X that then decays into the daughter which subsequently decays further but I might have not considered the fact that the daughter would keep getting 'replenished' by the decays of X which would affect the rate of decay (this would definitely be too complicated a consideration for a GAMSAT question). In the video, I am effectively treating it as two separate samples of X and daughter nucleus decaying simultaenously so the way I am working it out in the video, is the way that scenario would be considered. If I was to improve this question, I would scrap the daughter nucleus bit and just have two radioactive materials X and Y with different half lives and then determine the ratio between the two after some time. This is more likely where ACER would go too I'd assume

[@PriyaGupta-ff3pt]

@@jesseosbourne ahh gotcha, that certainly makes it way simpler. It was doing my head in trying to figure out how to figure out how it could possibly work!

[@bridget2806]

Thanks, you've helped me a lot studying for March 2024. Seriously appreciate this content. I think I've watched all your GAMSAT videos.

[@beautifulbeautiful6363]

these are exceptional man. the level of understanding you give in such a short period of time is amazing. Im so upset I didn't find these sooner now that the GAMSAT is a few weeks away. Oh well, Imma deffs use these for September if things don't work out. I hope you smash out March bro, you deserve it

[@jesseosbourne]

Really appreciate this feedback! This is exactly how I wanted to deliver these courses so it's great to hear that it's helping. Still plenty of time ahead of March in my opinion. Best of luck to you! 🙂

[@jaymie-leacollingwood2753]

I was so enamored by your puupy in the intro haha

[@jesseosbourne]

Haha he is quite the charmer haha

[@didisaythankyou]

@@jesseosbourne Kransky haha

[@hopelattouf4764]

These videos are so helpful coming from a person beginning to study for the exam. Really appreciate the time you've taken to make these!

[@jesseosbourne]

Fantastic! Glad they've been so helpful :)

[@isaacchua3132]

Hi Jesse! thanks for your vids and the effort you put into making them :) just a quick note for those watching that equivalent dose is actually defined as the absorbed dose multiplied by a radiation weighting factor (for xrays this value is 1), not a tissue weighting factor. The tissue factor comes into play in the effective dose, which is defined as the sum of the equivalent dose multiplied by the relevant tissue weighting factors. These are easily confused.

[@jesseosbourne]

Ah yes you're absolutely right! Good catch, thanks Isaac.

[@product_of_grace24]

thank you so much, honestly, you are heaven sent!

[@didisaythankyou]

Sorry for the long post. I'm going to try to like every video and comment often because your videos deserve it! Please don't feel that you have to read/answer everything. I'm from a science background but your videos are helpful as a refresher. I also find it interesting to me to see how your approach differs from mine, particularly since you scored much higher than me. Your videos are giving me hope that I can maintain or even do better on my S3 scores. I like your idea of considering what types of questions ACER might ask for each topic and I plan to do this as an exercise later. One of my biggest weaknesses (there are many) is that I'm a slow test taker. I can see the utility in rounding/approximating certain values but I hesitate to do so. I'm sure you have a video on this (that I will get to) but I'm curious to know your thoughts in this area specifically. In one of the examples you approximated 132 to 130, which makes sense because 2/132 is less than 2%. However, later you approximated 13 to 15, which seems like more of a stretch because 2/13 is roughly 15%. I'm not saying you're wrong, I'm just wondering at what point would you consider an approximation to be too much of a stretch and you make this decision. Interestingly the 2% figure I quoted in the paragraph above itself is an approximation. When I approximate I usually try to also remember if the actual value is more or less than the approximation. That way if the MCQ includes a 1.9% and a 2.1% I know to go for the 1.9%. This also slows my ability to approximate, particularly when I have to keep the direction in mind for more than one approximation. I noticed that in this case the possible answers (A to D) given differed by order of magnitude. Would you look at the possible answers before attempting the question to guide the amount of approximation you do in calculation? Approximate less if the answers are closer together and more if they differed by orders of magnitude? Does ACER often/always give options which differ enough to approximate this much? Did you ever run into problems on S3 exam where you approximated too much? Would you always use acceleration due to gravity as 10 and not 9.8 on S3? I guess this is an obvious 'yes'. I think these small things could really speed up my answers. Your Thursday thoughts looks really good. My S3 was 75 (luck) but my S2 was only 53. So I definitely need to focus a majority of my time on S2 this time around, which I'm already not doing haha. My S1 was 63 so I beat you there (if I remember your recent scores correctly), but only just. ;) I find that S1 isn't nearly as much of a time crunch as S2 and S3. I think I'm good at MCQ in general, while I'm certainly not well versed in poetry/humanities/other S1 content, I think I do ok by taking more time on S1 and considering which of the possible answers are more and less likely. I think this is also likely why my S3 has been decent (experience with MCQ and good at guessing). However, with S3, if I could learn ways to speed up, I'd have to guess less which would likely reflect favourably on my scores.

[@jesseosbourne]

Hey Ryan! Thanks so much, I appreciate the appreciation man, and really glad to see that its all so helpful. Approximation is a bit of a balancing act. Generally, yes I take a quick glance at the answers to get a gauge on how accurate I need to be (orders of magnitude, whole numbers, tenths etc). Something else I keep in mind when approximating is the rough proportional shift I'm making to each figure in the calculation. So for example, if I'm rounding the numerator and denominator of a fraction, I want to round each by the same rough % proportion so that the effects cancel out. If it's not a fraction, then I'm roughly making sure that I have one rounding up and one down by the same rough % so that the effects of rounding cancel out and don't compound. From what I've seen though, ACER generally keep the approximation required, pretty reasonable. With gravity, the question will always instruct you on what value to take for gravity but if it didn't state it, then I'd just go with 10 to keep the maths simple and see if my answer matches one of the options as feedback that I've done it right. S2 is definitely probably the section where you'll get the most reward for your efforts, so long as you take on feedback at the same time. Nice job with section 1. I haven't cracked that nut yet, but hopefully I'll have more to say on it after March haha

[@MonaSBF]

Thank you so much Jesse for this amazing video 😊🙏

[@stella7239]

Great content again, thanks so much Jesse!

[@denise9941]

Another great video! I'm not a big physics fan but I find this very interesting. The practice questions were really good and I enjoyed seeing Kransky here as well, ha ha. Thanks Jesse!

[@jesseosbourne]

Haha he's become the mascot of the channel

[@seankim1165]

Is it assumed in the GAMSAT to know the units such as mGg when it's not written in the question stem? Thanks

[@idontknowwhattoput8738]

Hello! Thank you as always for the effort you put in to each of these videos :) With the first example question, I was just wondering why we didn't need to use the proton and neutron numbers we calculated from the alpha and beta decay information. Is there any tip on knowing which parts of the question stem is unnecessary information and the like? Thank you!

[@jesseosbourne]

Hey there! Sorry for the wait on a reply until I returned from the break. Yep, so in that question, I run through the algebra of how to determine the expressions for the daughter nuclei under alpha and beta decay as an aside but we don't actually need this info to answer this question as it is to do with the level of decay that has occurred due to half lives rather than the specific identities of the daughter nuclei. Sorting through stem info is probably something that is best developed through practice and exposure to lots and lots of questions. But generally speaking, my method of working through stems is to read and categorise information as I go (skipping any theory that I'm already familiar with). I pay most attention to definitions of unfamiliar/technical terms, formulae and their descriptions, and any summaries of relationships between variables or items, given in the stem as these usually relate to specific questions. This helps me roughly anticipate possible important areas but the reality is that they could ask you anything so I would never 'disregard' any of the given info in case its needed. Finally, if there are any approximations or additional 'notes' given at the end of the stem, I make sure I pay close attention to them as they almost always get used.

[@idontknowwhattoput8738]

@@jesseosbourne Right, thank you so much!! I probably should get stuck into more questions. Also, apologies, I realised a bit after that you had gone on break! I hope you had a good well deserved rest :)

[@stella7239]

Hi Jesse, Thank you so much for your videos. They are truly so helpful and I am so grateful that there are free resources out there of this quality. I have been working toward GAMSAT for a few years now with multiple attempts and despite going through a (popular and v expensive) prep company i'm yet to be able to decently tackle S3 - I think your videos and website resources will help me hopefully. I'm very confused with question 1 - you work through the respective decays in the first portion, but then it seems (and I must be mistaken here) that this working doesn't matter, because in the second portion you simply take the given 1200 years and divide by the given half lives to work out the ratios 3 and 4, taking these to the power of 0.5 and going from there. What was the point of the first portion (where we find x = n-1) if we don't use those values in the second portion or to aid in the ultimate answer? I must be missing something :( Thank you in advance Jesse! We appreciate you!

[@jesseosbourne]

Hey Stella! Really glad to hear that you've found the videos helpful in your study! Ah yes so, ultimately we can just use the second part of the calculation to solve the answer for this one. The reason I run through the first part is to set up the pattern and the 'reasoning' to the question in terms of where that ratio actually comes from. I do this in a few of the crash course video explanations given that many are learning and applying this for the first time. here I start by taking the question on face value and demonstrating the step by step process and then showing that this same pattern could be sped up by a formula or expression (this is where the second part comes in). This way people can not only know how to answer the question but also see the links that can be made in finding a 'faster' way to tackle questions. Hope that helps :)

[@stella7239]

@@jesseosbourne Thanks for your reply Jesse. Im sorry if this is a really silly question, but in the first portion of working, how would working out that x = n-1 help us figure out the ratio? im having trouble understanding the step-wise process for the question

[@jesseosbourne]

To be fair this is a good call as it probably is a little misleading. This demonstration of what the mass and atomic numbers of the daughter nuclei become is more so to show an algebraic method of getting round the issue of not knowing the actual numbers (a common feature in GAMSAT questions) but it isn't directly relevant to answering the question. This deviation is just to add in some extra algebraic skills/problem solving processes for people. The general counting of half lives and decays is more useful and can be brought into the second much faster way of calculating the ratio

[@ninan4021]

Hi Jesse, sorry if this is a dumb question, but could you please explain at 17:55, why the ratio of the 1/2 to the power of no. of half lives were taken? Isnt the question asking about the ratio of the amount of the parent and daughter nucleus? Im not sure if I'm missing some info here..

[@jesseosbourne]

Hey Nina! No, not a dumb question at all! So because the question is based on the ratio of the parent to daughter cell, we don't actually require the amount initially so instead can just use the fact that it should be halving the amount remaining in each case every one half life. So the 1/2 is the ratio and then we can raise that to the power of the number of half lives to determine what ratio it would be after some time. The technical formula is usually written as Nt = N0 x (1/2)^n. Where Nt = amount after some time, N0 is the initial amount and n is the number of half lives elapsed. But it is often better to rearrange this slightly and divide the N0 across to give Nt / N0 = (1/2)^n this way the LHS of the equation (Nt/N0) is representing the ratio of the amount remaining and now you can see it is showing that it is equal to (1/2)^n Hopefully that helps clarify things!

[@ninan4021]

@@jesseosbourne makes sense now! thank you! :)

[@joshdag3330]

Hi jesse, thank you so much for the video but i had one question - for the 2nd practice question, you did (10^-3*1320)/75 but shouldnt you have converted the 10^-3 J into mJ first? im just confused because thats the equation you said earlier in the video for absorption. Thank you very much!

[@jesseosbourne]

Hey Josh, so the equation I mention in the dosage section you'll notice is already working in mGy as its units, hence mJ are used as the unit of energy. This is just because in the real world, 1Gy is gigantic and most dosage values will actually be much smaller and are better measured in mGy. In the question at the end, I am working in standard units of J and Gy, this is why there is no adjustment at the start of the calculation. You could adjust and convert the energy into mJ at the start but you'd have to make sure that you're aware that this will now calculate a dose in mGy. You can convert units at any point in a calculation so long as you keep track of what scale of magnitude you're working in throughout. I usually work in standard units to avoid confusion and then adjust to a more suitable magnitude (micro, milli, kilo, mega etc) once I have my final solution. This also means I only have to do one adjustment calculation instead of many along the way

[@joshdag3330]

@@jesseosbourne ohhhhh thank you so much hahahah I didn’t even realise 😂 if you keep it in mJ, you’ll get mGy but if you change it to J you’ll get Gy. Thank you for the clarification

[@rosiemcfadyen5127]

Thank you again for the really helpful vids!! I'm just wondering when calculating the absorbed dose in the practice question, do you always multiply the energy by the time in seconds? and is that a formula you recommend knowing by heart for the exam?

[@jesseosbourne]

Hey Rosie, so it kinda depends on the information you are given in the question. So long as we think of it as total energy divided by mass then we can get the dosage. In this case we have energy as a rate per time (J/s) so we need to multiply this by the time in order to determine the total energy delivered in that time frame. The units can help you with determining what to do in terms of the maths too. Since the value given is J/s and we need to get energy, we need to multiply by a number of s to cancel out the s to give just J as the unit. ie. J/s x s = J. Then we can get dosage by dividing energy by mass. If however, we were just given the energy delivered then we could just go ahead and divide that energy by the mass to get the dosage. Also, notice that J/s is a rate of energy per second which is equivalent to power in Watts so the figure could have also been reasonably quoted in Watts which we could then multiply by time to get energy. Definitely would NOT need to know this formula for the actual GAMSAT. They would supply this dose formula in the stem. I've created a cheat sheet on my notion page (link in description) that has all the formulas I see as either "need to know" or "helpful to know", that could be useful

[@rosiemcfadyen5127]

@@jesseosbourne thank you!! will definitely look at the cheat sheet

[@cat5220]

Should you ever find yourself in need of a kidney, buddy you can have mine

[@jesseosbourne]

Hahah deal! 🤝

[@sonidhillon5244]

@@jesseosbourne Bless he stays healthy.

[@BenMcleanhall]

I'm a bit confused as to why Jesse converted 75 to 7500- why could we not have done 1320/75?

[@kristysoe3989]

Hey Jesse, just wondering you divided the two ratios at 18:05 ? Thanks!

[@jesseosbourne]

Hey Kristy, yep so they're divided because the question focuses on the 'ratio' rather than the absolute amount. Whenever it's ratios, always divide them to determine the value of the ratio Someone did point out that technically the daughter nucleus is also decaying further which would affect the final ratio but this question ignores this impact to simplify it and demonstrate the principles of half lives and decay!

[@lertisgreat3588]

while i am here for the GAMSAT, can anybody tell me if you have a Kransky introduction video? if not put it at the stat of your next one please.

[@jesseosbourne]

Haha I actually had a lot of requests for this so I did one a little while back kzbin.info/www/bejne/g2XTY2CHoK2gmtk

[@samuelgak6240]

For the first question, how is half divided by half equal to half? Shouldn't the answer be 1 to the power of negative 1?

[@jesseosbourne]

Hey Samuel, so because they both have the same base (half) I’m applying the second index law (a^m / a^n = a^(m-n)) This means that the base of 1/2 remains You can prove this by expanding out the numerator and denominator (1/2)^3 = 1/2 x 1/2 x 1/2 (1/2)^4 = 1/2 x 1/2 x 1/2 x 1/2 Three of the 1/2 will cancel out and leave a half on the bottom of the fraction (1 over 1/2) = 2 Does that make sense?