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Physics: Post your doubts here!

Autumngirl

Autumngirl

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Autumngirl said:
I am confused about significant figures in paper 2. I've always been told to give as many significant figures in the answer as the least number in the data provided e.g. If data has both 2 and 3 significant figures, the answer must have 2 as it's the number in the least precise data. However, in the papers the mark scheme doesn't always follow this rule. Check out MJ11p23 question 3. Can somebody please explain why the examiners do this and give me a perfect rule about significant figures? Thank you!:)
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Someone please guide me! Wrong significant figures make you lose marks even if your answer is correct so it's like giving away marks. How do you guys determine the correct number of significant figures for any answer?
 
ZaqZainab

ZaqZainab

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Haya Ahmed said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s10_qp_22.pdf
Q6d and Q7b(ii) (1)

and

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s06_qp_2.pdf
Q7(a)

and


I have no idea about doing questions related to horizontal components, the ones with tan, etc.
Could someone give me a complete explanation of how to deal with such questions?
Q1b

QP: http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w10_qp_22.pdf

Please Help me ASAP ! Thanks ^_^
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Q6d there is something wrong with the voltage it is not divided equally you know the formula R=V/I if you make V the subject R*I=V it means there is something wrong with the resistance in the wire or the current
Q7 the alpha particle should be moving ie it should have a kinetic energy so it goes and hits the nitrogen 14 nucleus like if you keep an alpha particle next to a nitrogen it will just push it away its just the alpha particles scattering experiment with a Nitrogen nucleus instead of a gold


Q7 (a) they have mentioned all the lamps are similar and therefor they all have the same resistance but one of them is faulty
by the 2nd reading from the table you might know A=15 ohms and so you can assume B and C are also suppose to be 15 but one of them is faulty
by the third reading you can confirm that B is 15 cause A and B are in series and the total resistance is 30
left with C which is most probably the faulty one but wait find the resistance if C was not faulty it would be 22.5 but the answer says 15
shorted lamps are lamps going to earth short circuited faulty

I used to hate this questions never used to get them but they make sense now
I always like to make a figure on the side and work on it rather than work on the fig given but you make the call
 

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ZaqZainab

ZaqZainab

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Autumngirl said:
Someone please guide me! Wrong significant figures make you lose marks even if your answer is correct so it's like giving away marks. How do you guys determine the correct number of significant figures for any answer?
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Most of them if they are really strict about your significant figures they mention that
and if they don't i like to have my significant figures as they have the significant figures in the question
like for example in the question the acceleration is given to be 3.54 ms^-2
now i will have my answer to 3 significant figures
 
Haya Ahmed

Haya Ahmed

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ZaqZainab said:
Q6d there is something wrong with the voltage it is not divided equally you know the formula R=V/I if you make V the subject R*I=V it means there is something wrong with the resistance in the wire or the current
Q7 the alpha particle should be moving ie it should have a kinetic energy so it goes and hits the nitrogen 14 nucleus like if you keep an alpha particle next to a nitrogen it will just push it away its just the alpha particles scattering experiment with a Nitrogen nucleus instead of a gold


Q7 (a) they have mentioned all the lamps are similar and therefor they all have the same resistance but one of them is faulty
by the 2nd reading from the table you might know A=15 ohms and so you can assume B and C are also suppose to be 15 but one of them is faulty
by the third reading you can confirm that B is 15 cause A and B are in series and the total resistance is 30
left with C which is most probably the faulty one but wait find the resistance if C was not faulty it would be 22.5 but the answer says 15
shorted lamps are lamps going to earth short circuited faulty

I used to hate this questions never used to get them but they make sense now
I always like to make a figure on the side and work on it rather than work on the fig given but you make the call
Click to expand...
Thanks a lot can you answer this question too ! ^^

http://papers.xtremepapers.com/CIE/...nd AS Level/Physics (9702)/9702_w12_qp_22.pdf
Q5 (b) with explaination :)
 
ZaqZainab

ZaqZainab

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Haya Ahmed said:
Thanks a lot can you answer this question too ! ^^

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w12_qp_22.pdf
Q5 (b) with explaination :)
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1 meter of AD has a resistance of 10 ohms
40 cm (0.4m) will have 4 ohms of resistance (cross multiply)
P.D=R*I
the current in AC I=I2 which you found in (a) so I2=1.2
and so the p.d at AC=1.2*4=4.8
the resistace across AD=4 ohms
and the current is I3 which is 2
so p.d=2*4=8
8-4.8=3.2V
 
Talha Irfan

Talha Irfan

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_Ahmad said:
Describe an experiment to determine the wavelength of sound in air using stationary
waves. Include a diagram of the apparatus in your answer.
Click to expand...

Apparatus :
Loudspeaker (switched on)
Glass tube with an open end
Detector

Method :

1) Place the loudspeaker infront of the open end of the glass tube
2) Move the detector along the glass tube and measure the distance between two CONSECUTIVE regions which show zero/min intensity on the detector
3) Take set of values and average them to eliminate random error
4) Finally, equate the distance measured with 1/2(lambda)

so lambda (wavelength) = 2d (unit specified)
 
S

Snowysangel

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_Ahmad said:
We can answer this by thinking about the energy which is carried away by the particles (alpha or beta) and electromagnetic radiation (gamma) produced in the decay.Albert Einstein realised that we can think of energy as having mass. So if the mass of the nucleus decreases we must look around and find the energy which is carrying away this mass.The greater the apparent loss in mass the greater the amount of energy which is escaping.
To sum up we talk about "mass-energy" . In any closed system the total amount of mass-energy is conserved. If the mass goes down energy goes up and vice versa, but the total is constant
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But the mass does remain the same, or at least approximately the same right
 
Thought blocker

Thought blocker

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Wolfgangs said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s11_ms_21.pdf

How to solve Q5 b? I'm still kinda confused
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Note that we r asked to find I2 i.e. the current across a fixed resistor..
so maximum current will be:- V/R= 12/6 = 2.0 A
and i think that the minimum current value is zero just bcuz if we take the value of the variable resistor less than the value of fixed resistor then all the current will flow through the low resistance loop giving zero reading on the ammeter for the second loop
 
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