Physics: Post your doubts here!

T

trao11

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Could anyone help with Summer 2012/42, question 9 (c)

Which way do you draw the LEDs?

Thanks! :)
 
L

Llamas

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The mean kinetic energy of a molecule of an ideal gas is given by the expression
KE = 3/2 x k x T
where k is the Boltzmann constant and T is the thermodynamic temperature of the gas. A cylinder contains 1.0 mol of an ideal gas. The gas is heated so that its temperature changes from 280 K to 460 K. (i) Calculate the change in total kinetic energy of the gas molecules.

http://www.sheir.org/a-level-physics-43-nov2013.pdf
November 2013, 43, Question 2(B)
Could someone please explain the changes in the formula for this answer, I don't understand the markscheme.


http://physics-ref.blogspot.com/
This website does not have the solution for this variant.
 
TheJDOG

TheJDOG

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Llamas said:
The mean kinetic energy of a molecule of an ideal gas is given by the expression
KE = 3/2 x k x T
where k is the Boltzmann constant and T is the thermodynamic temperature of the gas. A cylinder contains 1.0 mol of an ideal gas. The gas is heated so that its temperature changes from 280 K to 460 K. (i) Calculate the change in total kinetic energy of the gas molecules.

http://www.sheir.org/a-level-physics-43-nov2013.pdf
November 2013, 43, Question 2(B)
Could someone please explain the changes in the formula for this answer, I don't understand the markscheme.


http://physics-ref.blogspot.com/
This website does not have the solution for this variant.
Click to expand...

The Eqn KE= 3/2(k)(T) is for a single molecule only, you need the change in KE of all the molecules.
So Total KE change = 3/2(1.38 x 10^-23)(460-280) (6.023 x10^23)= 2240 J
We multiplied by Na(Avogadro's number) because there is 1 mol of the gas, so there is this much molecules.
 
L

Llamas

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TheJDOG said:
The Eqn KE= 3/2(k)(T) is for a single molecule only, you need the change in KE of all the molecules.
So Total KE change = 3/2(1.38 x 10^-23)(460-280) (6.023 x10^23)= 2240 J
We multiplied by Na(Avogadro's number) because there is 1 mol of the gas, so there is this much molecules.
Click to expand...


Thank you so much, my notes were incomplete for this topic!
 
I

iwillrise

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I've been going through some past papers, and since the format is the same every single year, there seems to be a lot we can do to prepare for it. Kinda.

There are things I still don't understand though, even from the mark scheme. Please, someone help a brother out, quickly reply to a few of my questions. Maybe other people might also get some help from your answers. Thanks.

1) When drawing up the table and inserting our values on Q1, do CIE actually put marks on the values we put in. Is there like a range of values which they'll accept? For example, we have to set up our apparatus with six sets of readings, with six sets of "l", then we switch on the power supply and ammeter and record the current at each reading. The current value depends of the value of "l" we used. Will there be any marks on the current value?

2) For the graph question, every year there are 3 marks on the graph, and 1 mark apiece for line of best fit, gradient, and y-intercept. Firstly, the graph itself, after we join the points in a line of best fit, the graph won't be wrong, right? The 3 marks go on the scale used and axes and stuff? So as long as I draw the graph properly, using the values I got earlier, I'll get all 3 marks? Or is there a trend or does the graph actually have to look like the corrector's? Also, is the gradient going to be correct as long as we got it from our graph, or is there a range for that? For the y-intercept, I usually just extend my graph, and see where it cuts the y-axis.

3) For % uncertainty, can someone please give me a rough guideline? I know how to do it, but in the mark schemes they talk about "absolute uncertainty" and have a range for that. What do they meeeeaaaannn?

4) This Q is there every year, and I NEVER get it, what do they want me to write when they ask "JUSTIFY THE NUMBER OF SIGNIFICANT FIGURES USED"????

5) Lastly, is there anything I can memorise for that last question, asking about limitations and improvements, that are likely to be constant throughout the years. i.e= not enough readings....



Thanks in advance for any answers.
 
Ahmad Sammy

Ahmad Sammy

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Ok guys I have a question about momentum.
Assume a scenario where two masses of equal masses and acceleration are moving towards each other about to collide.
Can we predict their behavior after collision. Do they bounce back with same velocity or acceleration? Or stick together and stay stationary? Or is it impossible to predict?
 
Komail Sabba'

Komail Sabba'

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Paper 4: Doubt on repetitive question.
Milikan's experiment, where they give you around 5 values of charges on oil droplets and you are required to find the elementary charge.
 
TheJDOG

TheJDOG

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farhan980 said:
Can someone please help me with oct nov 2014/43 Q.10/b/ii
Click to expand...
Just draw half rectangles with their heights at +5v and -5v since it can never exceed the supply. Each time, draw the half rectangle opposite to the vin , if the cycle of vin is +ve, draw vout at -ve and vice versa
 
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