Mistake in JEE Advanced-2014, overlooked?

The above problem appeared in JEE- Advanced 2014 paper-1. Please try it before joining the discussion.

The answer given in the official key, and everywhere else is $4$ . Here is a solution:

But I believe that the answer should be $8$ . In the solutions released by coaching institutes, they have made an unsubstantiated assumption that the maximum error in measuring the length is equal to $1$ Least count of the Vernier scale. I think this is wrong. The problem clearly states that two independent observations are made. This must imply that the maximum error in each observation is $1$ least count. And hence, it follows that the maximum error in the difference of the readings is two least counts.

#Mechanics #JEE #Basics #Mistakes #Erroranalysis

Easy Math Editor

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Comments

@Mvs Saketh @Ronak Agarwal @Shashwat Shukla @Azhaghu Roopesh M @Krishna Sharma @Tanishq Varshney @Rohit Shah @Nishu sharma @Kushal Patankar

Raghav Vaidyanathan - 6 years ago

I have found out the reason, and it seems that this question is right and I was wrong. We have to assume that the error in the first reading is zero as they have given that the Vernier scale division exactly coincides with a main scale division.

Raghav Vaidyanathan - 6 years ago

Error analysis, Vernier Callipers are something I have not understood till now.

Ronak Agarwal - 6 years ago

look at the resonance tube problem (multiple correct choice question) , do you think it is correct? the solution assumes that the resonance tube is an open tube (on one end)

however, the question says that there is a different gas in the tube, (not air), wont the gas escape if the tube is open , or is the whole lab filled with argon/neon/etc . hence i assumed that it was closed and attempted, only to realise later that we had to assume it was open, but doesnt make sense right

Mvs Saketh - 6 years ago

@Mvs Saketh – They have asked us to assume that the gas is always inside the tube...

A student is performing an experiment using a resonance column and a tuning fork of frequency 244𝑠𝑠−1. He is told that the air in the tube has been replaced by another gas (assume that the column remains filled with the gas). If the minimum height at which resonance occurs is (0.350±0.005) m , the gas in the tube is...

Raghav Vaidyanathan - 6 years ago

@Raghav Vaidyanathan – i do not think it makes sense to assume such a thing, but i take your point :)

best of luck

Mvs Saketh - 6 years ago

@Mvs Saketh – Yes, you are right. It might make sense if the gas is significantly more denser than air, so at least it would stay there for a while. But as much as I hate to say it, these guys are extremely good at making problems, chance of error is abnormally low. Best of luck to you too.

Raghav Vaidyanathan - 6 years ago

@Raghav Vaidyanathan – Compare these guys( the IIT ones) to the CBSE bastards.

Ronak Agarwal - 6 years ago

@Raghav Vaidyanathan – indeed, wonder how it will be this year, i am extremely excited, and yet there is this slight unexplainable feeling inside of some fear

Mvs Saketh - 6 years ago

@Mvs Saketh – Because of this I have decided to not exert myself and relaxing at home doing a extremely limited number of problems and enjoying myself the whole day by going to parks for playing cricket and doing various other things at home, what are you doing MVS Saketh.

Ronak Agarwal - 6 years ago

@Ronak Agarwal – well, unfortunately, i have no access to friends, so i am just looking at chem stuff and p-block and things, chem was harder in 2014 (i got 89 in mock) and much easier in 2013 (114 in mock) , so if i assume the derivative doesnt change, i might be in trouble

so just, doing this and that, i am pretty confident of maths and physics though, lesser problems, no clumsiness or amiguity and sufficient rough space are some things i really love about JEE advanced

Mvs Saketh - 6 years ago

@Mvs Saketh – That is true... You feel like doing it well when you see a paper of JEE advanced standard. Incorrect problems take the spirit out of the exam. I too got low marks in 2014 paper(84) and lower marks in 2013 paper(72 XD) but I did the 2013 paper months ago... so I guess that doesn't count... Hope chemistry is easier this year...

Raghav Vaidyanathan - 6 years ago

@Raghav Vaidyanathan – yes, i mean, i dont want it to be easier, but excess problems from p-block stuff that are so far and exotic and are so out of course really take the fun out, and also, questions like which amino acid is natural

in 2013 paper, it was hard, but the hard questions were solvable mostly through logic , whereas no matter how much logic you use, u cant even guess what xenate ion forms upon excess heating

but yet, we have to face however it is, and hence i have practiced and didnt leave out anything, Now i just wanna face it, and the slight fear i have just makes want to talk to people and say best of luck to everyone xD

Mvs Saketh - 6 years ago

@Mvs Saketh – I agree with you on the "unsolvable unless you memorize whole p-block theory" type questions. Feels nice to finally have it around the corner after two years.

Raghav Vaidyanathan - 6 years ago

@Raghav Vaidyanathan – yeah, i just wanna nail it so hard :D

Mvs Saketh - 6 years ago

@Mvs Saketh – I have read the p-block theory nearly 4 times and still I fear Chemistry, toughest subject I have faced in my life.

By the way are you comfortable with matrices.

Ronak Agarwal - 6 years ago

@Ronak Agarwal – well, there can be hard questions in matrices, but atleast in 2013 and 14, questions from matrices were too easy, but yes, in 2010, there was a non trivial question about matrices in comprehension which i found pretty hard, which u might have seen, so provided the trend doesnt change, i am comfortable , how do you feel about calculative problems? like did you see the "find the refractive index problem" in paper 2 physics, it was insanely calculative, and answers were so close, u cant even approx

Mvs Saketh - 6 years ago

@Mvs Saketh – Calculative problems I love them , what I don't like is logic questions in chemistry,

My analytical skills are good ( Thinking in a striaght forward manner), my logical skills are pretty weak. I have a low IQ you can say.

Ronak Agarwal - 6 years ago

@Ronak Agarwal – analytical skills are equivalent to logic , its funny you say your IQ is low,

well, but you would still prefer logic questions in chem as compared to p-block questions that you wont happen to remember i think ?

Mvs Saketh - 6 years ago

@Mvs Saketh – I simply hate the chemistry we study for jee, I love organic chemistry and I am seriously strong in this topic.

I hate rote chemistry.

Ronak Agarwal - 6 years ago

@Ronak Agarwal – indeed , that is true, just 3 more days with that chem then, then OCSC time!

Mvs Saketh - 6 years ago

@Mvs Saketh – My thinking is stuck to only one thing what if I did a lot of silly mistakes, my two year effort goes a complete waste ( not that much waste since I have learned many new things) but still.

Ronak Agarwal - 6 years ago

@Ronak Agarwal – i do not think you will :)

Mvs Saketh - 6 years ago

Math	Appears as
Remember to wrap math in `\(` ... `\)` or `\[` ... `\]` to ensure proper formatting.
`2 \times 3`	$2 \times 3$
`2^{34}`	$2^{34}$
`a_{i-1}`	$a_{i-1}$
`\frac{2}{3}`	$\frac{2}{3}$
`\sqrt{2}`	$\sqrt{2}$
`\sum_{i=1}^3`	$\sum_{i=1}^3$
`\sin \theta`	$\sin \theta$
`\boxed{123}`	$\boxed{123}$