Physics: Post your doubts here!

[leosco1995]

AoA! angelicsuccubus: I think you sort of misread the question. The answer requires a sketch of the same stationary wave 0.25 T later. There's no change in period. So the correct sketch would simply be a straight horizontal line (on the dotted line). leosco1995: In case you're confused, check this simulation: http://en.wikipedia.org/wiki/File:Standing_wave.gif
At t = 0s, the graph is as shown in the question
At t= 0.25 T, the graph is a straight horizontal line
At t= 0.5 T, the graph is again sinusoidal with the antinode 'crest' now being the 'trough' while the nodes remain exactly the same.
At t = 0.75 T, the graph is again a straight horizontal line
At t = T, the same graph as the question again.
(This only applies to a stationary wave. A progressive wave sketch is never horizontal at any time.)

Oh, I see... good thinking.

Thanks for the correction.

 

[Most_UniQue]

Check this question , the value I obtained was 264900 which I rounded to 265k fr 3 SF but their answer is 2.7x10^5 which is 2 SF . Is it cuz the heigh is in 2 SF?

 

[leosco1995]

http://www.xtremepapers.com/papers/...nd AS Level/Physics (9702)/9702_s11_qp_23.pdf
Q3 (d) (i) I got 1 correct, but I don't get the 2nd part. Help would be appreciated.

 

[hussamh10]

http://www.xtremepapers.com/papers/...nd AS Level/Physics (9702)/9702_w10_qp_22.pdf
PLZ can any one expalin me the Q6 B part how to find the total resistance between A and B

 

[littlecloud11]

Check this question , the value I obtained was 264900 which I rounded to 265k fr 3 SF but their answer is 2.7x10^5 which is 2 SF . Is it cuz the heigh is in 2 SF?

View attachment 11102

Yup. But the mark schemes are not always consistent. Here, they kept the answer to the same no. of sig. fig. as the data, but you'll notice that they don't always follow this.
So, even if you fail to keep it the same as the data, but give the answer to a reasonable number of sig fig. like 3, you won't be penalized. so relax.

 

[hussamh10]

hi guys.. can u help me with this?
View attachment 11060

That Is sir a tough question B part!!!

 

[littlecloud11]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s11_qp_23.pdf
Q3 (d) (i) I got 1 correct, but I don't get the 2nd part. Help would be appreciated.

The man was moving with a uniform velocity of 2m/s before decelerating, so for the deceleration u= 2, v=0 a= -.31
v=u +at
0= 2 - .31t
t= 6.45 sec

 

[hussamh10]

hi guys.. can u help me with this?
View attachment 11060

• first take out path difference
• which is 28cm
• the using v=f * lambda (By pythogras theoram)
  • 330= 1000(lambda)
  • and 330=4000(lambda
    • which are 33cm and 8.25 cm respectively
    • path difference for minima= (2n+1)(lambda/2)
    • putting n value as 0,1,2,3 we get 56cm, 18.7cm, 11.2cm nd 8 cm
    • since wavelength 56cm nd 8 r not within range of 8.25 to 33 so minima re waveleng 11.2 and 18.7. 2 minimas

 

[Most_UniQue]

Yup. But the mark schemes are not always consistent. Here, they kept the answer to the same no. of sig. fig. as the data, but you'll notice that they don't always follow this.
So, even if you fail to keep it the same as the data, but give the answer to a reasonable number of sig fig. like 3, you won't be penalized. so relax.

tmx

 

[littlecloud11]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w10_qp_22.pdf
PLZ can any one expalin me the Q6 B part how to find the total resistance between A and B

Ok, if the p.d. across AB is 4 vol then the p.d. across the 1.2k ohm resistor is 5 volt.
the ratio of the p.d. is the same as the ratio of the resistance between AB and the 1.2 kohm resistor
so, 4/5 = resistance across AB/ 1.2
resistance across AB = 4/5 * 1.2 = .96 kohm = 960 ohm

 

[littlecloud11]

tmx

No problem.

 

[hussamh10]

how do we know that the ratio is same ??
Cant we do it by finding out the current supplied to thermistor and by finding out its resistance we can calculate the total resistance across AB

 

[Saad (سعد)]

As-Salaamu 'Alaykum wa Rahmatullah.

Someone please help me understand the concept of phase difference, and how a constant phase difference results in coherent waves.

I do have the general idea, but a revision could be useful, just so I don't miss anything. And a bit easy on the radians, please, I'm not a Math student.

 

[leosco1995]

http://www.xtremepapers.com/papers/...and AS Level/Physics (9702)/9702_s05_qp_2.pdf
Q5 (b) (iii) please.

 

[geek101]

http://www.xtremepapers.com/papers/...and AS Level/Physics (9702)/9702_s05_ms_2.pdf here for Q2a... Brownian motion, why does it say speck of light!

 

[leosco1995]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s05_ms_2.pdf here for Q2a... Brownian motion, why does it say speck of light!

because you do see tiny specks of light when viewing the particles through a microscope?

 

[Saad (سعد)]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s05_qp_2.pdf
Q5 (b) (iii) please.

In dsinϑ = nλ, ϑ is the angle between the diffracted ray and the grating's normal vector (the straight line from the centre of the grating - the normal zero order - to the screen).

If the light strikes at an angle, it will also leave at an angle (as shown in the diagram in the question). If we use the formula in this case, the value of ϑ would not be accurate, as the zero order of the diffracted light is bended upwards, while the formula assumes that the zeroth order is normal (a straight line between the grating and the screen).

That's what I understand. I don't get the Mark Scheme answer. o-o

Ratta we need.

 

[geek101]

As-Salaamu 'Alaykum wa Rahmatullah.

Someone please help me understand the concept of phase difference, and how a constant phase difference results in coherent waves.

I do have the general idea, but a revision could be useful, just so I don't miss anything. And a bit easy on the radians, please, I'm not a Math student.

first here is how you convert the degrees and radians...
radians to degrees : multiply by 180/π
degrees to radians: multiply by π/180

Phase difference is simply is the fraction of the cycle (the angle) by which one wave moves behind the other.
you can calculate is by using this equation: (with degrees)
360 (x/λ) where x is the difference in the distance between the two waves...
or 360(t/T) where the waves are out of step by time t.
use 2π for radians, since 360 = 2π

For coherent waves....they have a constant phase difference...this is usually the case with waves fron the same source. It does not matter whether the waves are in phase ....but coherent waves must have a constant phase difference...which means that the difference between them is the same throughout. They must also have the same wavelength and the same frequency.
this is quite brief..but hope it helps.

 

[geek101]

because you do see tiny specks of light when viewing the particles through a microscope?

but arnt you supposed to talk about the specks of smoke particles?

 

[leosco1995]

but arnt you supposed to talk about the specks of smoke particles?

The question says "describe what is seen..", yes you do talk about the smoke particles, but since they appear as tiny, white specks of light you should mention that in the answer to that question since it's an observation. Likewise you would mention that the motion of these specks of light is haphazard since that is also an observation.