Physics: Post your doubts here!

rz123

rz123

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Its B as you see the resistivity is increasing as we travel ahead, p.d also increases with it. so the graph of I/d will get more steeper as we move ahead from P clear?
 
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ramshanasir

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hey i need help in this question!

A student uses a micrometer to measure the diameter of a wire of length (10 +- 0.1)cm. The values obtained are 1.05mm, 1.04mm, and 1.09mm. Which of the followinf best expresses the volume of the wire?

A. 9 x 10-8 m3
B. 8.8247 x 10-8 m3
C. 8.825 x 10-8 m3
D. 8.8 x 10-8 m3
 
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deepa1802

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rviboy said:
Its B as you see the resistivity is increasing as we travel ahead, p.d also increases with it. so the graph of I/d will get more steeper as we move ahead from P clear?
Click to expand...

Still having doubt...R=(el)/A..right? if resistivity increases, R increases. V=IR. I is constant. If R increases, V shouldn't increase as well? And concerning the answer 'B', why does V vary even when resistivity is the same?
 
rz123

rz123

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what i got from my limited knowledge is that d/v graph can't be a straight line as resistivity is changing increasing as we move ahead. the constant of proportionality here is current so yeah p.d should also increase. i m also confused :Search: :pardon:
 
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Swoorup

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You should consider the length also.Look here:

R=(resistivity*length/Area)
Now,
Since length is decreasing at a constant rate V also decreases at a constant rate. The resistivity is p and is constant for a certain length. So V keeps on decreasing constantly.

Now consider at the beginnining of 2p resistivity. The length is still decreasing constantly, but the resistivity is increased which results in V to decrease at more rate than before in corresponding to the length.
 
yuliana95

yuliana95

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Please help me with this question:
The resistance R of an unknown resistor is found by measuring the potential difference V across the resistor and the current I through it and using the equation R =V/I .The voltmeter reading has
a 3 % uncertainty and the ammeter reading has a 2 % uncertainty.
What is the uncertainty in the calculated resistance?

Option:
A 1.5 %
B 3 %
C 5 %
D 6 %

Why is the answer C? and not A? isn't resistance V/I?? please explain..
 
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Swoorup

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The uncertainties are not divided, rather the percentage or fractional uncertainties should be added for those type of equation.

Look here: Suppose you have A=B+C
Now that you are given uncertainties of B and C, you can directly add the uncertainties. It is the same if you are given B-C, you would have to add.

Now referring to the question you ask,
Given, R=V/I

The uncertainties is calculated by:
U:R/R = U:V + U:I , where U: is uncertainity of.
So you would have to add the fractional uncertainty, which is the same if expressed in percentage U:R/R * 100 = U:V/V * 100 +U:I/I * 100
If you cant understand what I said, please read your book. There are numerous examples already explained
 
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ramshanasir

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nobody answered my question :'(

A student uses a micrometer to measure the diameter of a wire of length (10 +- 0.1)cm. The values obtained are 1.05mm, 1.04mm, and 1.09mm. Which of the followinf best expresses the volume of the wire?

A. 9 x 10-8 m3
B. 8.8247 x 10-8 m3
C. 8.825 x 10-8 m3
D. 8.8 x 10-8 m3
 
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Swoorup

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The answer is A, I guess.
Well I am unsure if so. Can you please tell me the answer, then I think I can explain the reason here.
 
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Swoorup

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Well, I thought the answer was A because averaging the diameters and finding the volume gives 8.9 as the answer.
But it seems that it is in terms of significant figures the answer should be.
I don't know for sure though
 
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