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Physics: Post your doubts here!

A

ahmedish

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Physicist said:
not that the above is percentage uncertainties.

actual values should be given to a SINGLE sf (without taking into account the zeros.)
the above could also be written as (13 +- 2) x10^2 - hence 1sf

See how the final answer is given at the link there.
Click to expand...
can i actually write "(13 +- 2) x10^2 " or does it have to be 13x10^2 and then 2x10^2 since theres a +_ sign between?
 
A

ahmedish

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Physicist said:
yes you can use (13 +- 2) x10^2.
actually, you should be using it this way
Click to expand...
yeah but I mean, they are not on the same like dots?
Like the answer format is like ............ +_ ................
Can I put a big bracket around it then x10^-2?
 
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ahmedish

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Can someone explain precision and accuracy please??\
also long range order and short range order for materials
 
C

cambridgewbhs

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ahmedish said:
Can someone explain precision and accuracy please??\
also long range order and short range order for materials
Click to expand...
Precision is how closely repeated measurements of the same quantity agree. It can be thought of as the number of decimal points the quantity is measured to, and is regardless of whether the measurement is correct or not

Accuracy is how close the measurements are to the true value.
 
qwertypoiu

qwertypoiu

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ahmedish said:
Can someone explain precision and accuracy please??\
also long range order and short range order for materials
Click to expand...
Long range order is like solids, the particles are aligned for large distances.
Short range order is like liquids. They have some order for a small number of particles, but over larger numbers they aren't perfectly aligned.
 
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ahmedish

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cambridgewbhs said:
Precision is how closely repeated measurements of the same quantity agree. It can be thought of as the number of decimal points the quantity is measured to, and is regardless of whether the measurement is correct or not

Accuracy is how close the measurements are to the true value.
Click to expand...
Yeah I don't get why precision is linked to decimal places? if the values we get for gravity are 9.80 and 9.82, these are precise, what do decimal places have to do with this?
qwertypoiu said:
Long range order is like solids, the particles are aligned for large distances.
Short range order is like liquids. They have some order for a small number of particles, but over larger numbers they aren't perfectly aligned.
Click to expand...
I mean long range and short range for crystalline, amorphous and polymers
 
nehaoscar

nehaoscar

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upload_2015-10-17_17-45-1.png
Can someone explain this
Its like the Millikan drop experiment
For this I calculated average but the mark scheme simply says that elementary charge is 1.6*10^-19 or 1.7*10^-19 because this is a factor of them all...
But it's not exactly a factor ... So how to do this one??
 
qwertypoiu

qwertypoiu

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Saad the Paki said:
Please help me solve Q9!View attachment 57255
Click to expand...
So there are two parts to this race:
1. Increasing speed from 0 to 10
2. Going at constant speed of 10

We can find time taken for both, and add them up.

1. u=0, v=10, a=2.5, s=?, t=?
First let's find distance covered:
v^2 = u^2 + 2as
100 = 0 + 2(2.5)s
s=20m
So he covered 20m.
Also time taken:
v=u+at
10=0+2.5*t
t=4s
So he took 4s

2. Since he covered 20m in first section, he has to complete 80m more. (100-20)
time = distance / speed = 80/10=8s

Total time = 4 + 8 = 12s
 
Saad the Paki

Saad the Paki

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qwertypoiu said:
So there are two parts to this race:
1. Increasing speed from 0 to 10
2. Going at constant speed of 10

We can find time taken for both, and add them up.

1. u=0, v=10, a=2.5, s=?, t=?
First let's find distance covered:
v^2 = u^2 + 2as
100 = 0 + 2(2.5)s
s=20m
So he covered 20m.
Also time taken:
v=u+at
10=0+2.5*t
t=4s
So he took 4s

2. Since he covered 20m in first section, he has to complete 80m more. (100-20)
time = distance / speed = 80/10=8s

Total time = 4 + 8 = 12s
Click to expand...
Oh thank you so much!
Would appreciate it if u could help in this one as well ( Q6 ) :D
 

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qwertypoiu

qwertypoiu

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Saad the Paki said:
Oh thank you so much!
Would appreciate it if u could help in this one as well ( Q6 ) :D
Click to expand...
P = I^2 * R
So percentage uncertainty in P = 2 * percentage uncertainty in I + percentage uncertainty in R

Percentage uncertainty in I = 0.05/2.5 * 100% = 2%
Percentage uncertainty in R = 2% (given in question)
Percentage uncertainty in P = 2*2% + 2% = 6%
 
A

ahmedish

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Physicist said:
KE because the alpha would be moving (KE = 1/2 mv^2 - if something is moving, it has KE)

charge of electron = 1.6x10^-19
1 M (mega) = 10^6
1MeV = (10^6) x (1.6x10^-19) = 1.6x10^-13
5.3MeV = 5.3 x 1.6x10^-13
Click to expand...

http://papers.xtremepapers.com/CIE/...and AS Level/Physics (9702)/9702_w07_qp_2.pdf
4c
why don't we use 2x1.9x10^3 for the force since it acts from both directions? shouldn't we double it? Also whats minimum area and whats maximum area? what exactly is happening here because i dont get it at all. would also like explanation for 4d
 
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