Physics 5054

[Silent Hunter]

what about that copper wire one? asking about tempe and thickness ................given in a table in the MCQ .... was it D?

 

[SuperDude]

The answer was A for MCQ 40 as the number of atoms dont chnge after the half life. Its just that they convert from unstable to stable.The qst asked for the no of atoms after 12 years not the no of unstable atoms thus answer wud be 40 million.

@nomercy:- Tum tu bura hi man gae!!!

Wait, what? Half-life is essentially the time taken for half of a substance to decay and if something has a half-life of 12 years, it means half of it decays in 12 years. Hence, if it starts with 40 million atoms, then after 12 years, it will have 20 million atoms. It doesn't matter if they give you the mass of the substance or the number of atoms, half of it will decay nonetheless.

 

[criplerslash]

half life is the time taken for the rate of emissions to reduce by half
the mass of the sample does not alter

i'm quoting this directly from a book

btw did the question ask simply no of atoms or no of deuterium atoms

 

[ibadsiddiqi]

did the question ask the number of undecayed atoms left or simply the number of atoms left??

 

[workaholic]

Well it said no.of atoms for sure....
My friend gave me this shock after the paper and he said that hed read the qst 4 times?? So its bound to be correct

 

[jojo381]

well i think sm students are trying to become oversmart in the half life mcq...it was surely 20 million atoms......i am posting a ink to the defination of half life which arrives in MJ,M.S21...check the def in qs 11b(i)....it clear staes no. of atoms to become halved...http://www.xtremepapers.me/CIE/Cambridg ... _ms_21.pdf

 

[ibadsiddiqi]

YAAY!!

 

[rogue94]

the number of atoms emitting radiation are definitely halved! the question however did not ask about how many radioactive atoms remained...it asked about how many atoms remained. The no. of atoms remains the same. Unstable nuclei become stable nuclei by emitting radiation!

 

[no.mercy]

@jojo...CHEERS DUDE>>YOU ROCK

 

[Silent Hunter]

what about that copper wire one? asking about tempe and thickness ................given in a table in the MCQ .... was it D?

please answer this too

 

[no.mercy]

thickness should be more and temperature low..i dont remember but i think kei it was A

 

[rogue94]

i dont remember the options no. but it was the one with increase in thickness and decrease in temperature.....both of these decrease resistance

 

[rogue94]

what abt MCQ 2....the pipe one....the internal diameter is measured by vernier calipers for sure, but wat is the the length measured by???? tape or meter rule??

 

[no.mercy]

metre rule for sure

 

[rogue94]

y cant we use tape? :|

 

[no.mercy]

for a length like 80 cm metre rule is more feasible as it has an accuracy of 1 cm and if you see the past papers..for answers like it the length of such kind is alwayz measured by metre rule

 

[rogue94]

doesn't tape have the same accuracy?? still....metre rule does seem more sensible! :\

 

[no.mercy]

dont worry bro.. even if one MCQ is wrong you still get an A star with 98 percent

 

[Silent Hunter]

oh i think i got tht temperature one wrong ............... what about that one about velocity and acceleration? it was in the start of MCQs asking what would be acceleration , constant at 0 , constant at 10 .... n some more options..........what was its answer?

 

[rogue94]

it was from 10 to 0