A2 Physics | Post your doubts here

[RGBM211]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s06_qp_4.pdf
http://www.xtremepapers.com/papers/...and AS Level/Physics (9702)/9702_s06_ms_4.pdf

can someone please explain 1c)

?????

 

[Mobeen]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s06_qp_4.pdf
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s06_ms_4.pdf

can someone please explain 1c)

?????

c i:
total energy = - GMm/2r .
when total energy 'decreases' the value of GMm/2r increases (just like -2 decreases t0 -5 ... overall value of -5 is less then -2 but the magnitude 5 is greater than 2) same as that value of GMm/2r increses when total energy decreases.. when GMm/2r increases .. r decreases .. because it is in the denominator .. get it ?

and part ii
as explained above when total energy decreases r decreases. when radius of the orbit decreases speed would increase acording to the centripetal force = (mv^2)/r .... r decreases so v increases.

 

[Idris]

The emf and current in the primary coil of a transformer are in phase right?

Yea right.
You earlier inquired about the graph of induced emf due to primary current, the resulting graph was derivative of changing magnetic flux, since primary current and magnetic flux have same graph, the induced emf was E=-d(phi)/dt. I hope you get it.

 

[RGBM211]

c i:
total energy = - GMm/2r .
when total energy 'decreases' the value of GMm/2r increases (just like -2 decreases t0 -5 ... overall value of -5 is less then -2 but the magnitude 5 is greater than 2) same as that value of GMm/2r increses when total energy decreases.. when GMm/2r increases .. r decreases .. because it is in the denominator .. get it ?

no its confusing

 

[SkyPilotage]

are all of you going to go sleep soon? ...

haha yes I also have an awkward left alone feeling when everybody goes to sleep haha.
But you and I have to get some if we want to pass hehe

 

[RGBM211]

well i am awake as well still not done solving papers i guess mmm the unlucky one here 2 exams tommorow still havent started Maths M1.... oh well nvm

 

[SkyPilotage]

Yea right.
You earlier inquired about the graph of induced emf due to primary current, the resulting graph was derivative of changing magnetic flux, since primary current and magnetic flux have same graph, the induced emf was E=-d(phi)/dt. I hope you get it.

I just checked again, primary current and voltage on primary coil are out of phase by 90 degrees. This is because current is a followup of the voltage, where voltage leads by 90 degrees. you really dont need to know abt it.
secondary emf is out of phase (180 degrrees ) compared to primary emf.
secondary current compared to secondary emf// not too sure.

 

[user]

haha yes I also have an awkward left alone feeling when everybody goes to sleep haha.
But you and I have to get some if we want to pass hehe

i aint sleeping now..i have to finish up application ..last 2 topics...
then revise for maths exam..both are tomorrow...and then will i think of sleeping

 

[RGBM211]

wooow only 2 topics i have 8 topics to cover :'(
maths i havent even started plz pray for me guys

 

[user]

well i am awake as well still not done solving papers i guess mmm the unlucky one here 2 exams tommorow still havent started Maths M1.... oh well nvm

same here..
do try nov 11 second variant for maths...i'll do it too..inshaAllah..cuz the gt for that paper is low..paper might be difficult..so to check myself..m planning to do that...

 

[RGBM211]

any advice how to revise quickly everything ^

 

[SkyPilotage]

any advice how to revise quickly everything ^

quick joke which you most understand, how many polar orbits of an overhead satellite is required before the start of your exam?
Show ur working

TIPS :-
Revise definitions!
Quick read of the syllabus!
Quicky notes!
Revise only hard questions from the latest past papes!
Have a kit-kat and have a break and wait for your exam

 

[Mobeen]

no its confusing

i cant explain it in any other way ! :/

 

[angelicsuccubus]

haha yes I also have an awkward left alone feeling when everybody goes to sleep haha.
But you and I have to get some if we want to pass hehe

well I can't sleep.. I still have 4 chapters to go through.. all the pastpapers and study all of IT.. and 2 more mech pastpapers.. so I guess I'll be the only one here -_-

 

[user]

quick joke which you most understand, how many polar orbits of an overhead satellite is required before the start of your exam?
Show ur working

 

[waleedsmz]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s06_qp_4.pdf
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s06_ms_4.pdf
can someone please explain 1c)?????

First of all thanks for putting both the mark scheme and the question paper. ^^

i) Ok let's start by thinking about this in a way not involving any calculation. We know that if two bodies are attracting each other, then as the separation between them decreases, their potential energy decrease. From there, when he told you that the total energy decreased, this must mean that r (separation) decreased.

Now using calculations: The sum of energies ( -GMm/2r ) decreased, this means the negative magnitude actually became greater. Why? Because -7 is smaller than -5 for example. This has to mean that r became smaller.

ii) From (i) we know that r decreased, and according to (b)i) K.E. = GMm/2r... R decreased so K.E. increased. Notice how the K.E. is positive and the Total Energy is negative. That's why a small radius produces less total energy but more kinetic energy. Kinetic energy is proportional to speed so speed also increased.

You can also use part (a) of this question which states that V is the root of GM/r ---> r decreased so V increased.

Hope this helped. : )

 

[user]

well I can't sleep.. I still have 4 chapters to go through.. all the pastpapers and study all of IT.. and 2 more mech pastpapers.. so I guess I'll be the only one here -_-

i'll probaby be there too ..may be for the next 3 hours...i so wanna finish before that so i cud wake up early tomorrow

 

[RGBM211]

First of all thanks for putting both the mark scheme and the question paper. ^^

i) Ok let's start by thinking about this in a way not involving any calculation. We know that if two bodies are attracting each other, then as the separation between them decreases, their potential energy decrease. From there, when he told you that the total energy decreased, this must mean that r (separation) decreased.

Now using calculations: The sum of energies ( -GMm/2r ) decreased, this means the negative magnitude actually became greater. Why? Because -7 is smaller than -5 for example. This has to mean that r became smaller.

ii) From (i) we know that r decreased, and according to (b)i) K.E. = GMm/2r... R decreased so K.E. increased. Notice how the K.E. is positive and the Total Energy is negative. That's why a small radius produces less total energy but more kinetic energy. Kinetic energy is proportional to speed so speed also increased.

You can also use part (a) of this question which states that V is the root of GM/r ---> r decreased so V increased.

Hope this helped. : )

awsome man thanks

 

[optimistic]

http://www.xtremepapers.com/papers/...nd AS Level/Physics (9702)/9702_w11_qp_41.pdf
Can anyone here explain me the answer to Q7 part c?

 

[RGBM211]

quick joke which you most understand, how many polar orbits of an overhead satellite is required before the start of your exam?
Show ur working

TIPS :-
Revise definitions!
Quick read of the syllabus!
Quicky notes!
Revise only hard questions from the latest past papes!
Have a kit-kat and have a break and wait for your exam

dint get you there

Oh well any advice how to study applications as quick as possible others are managable but i m still having confusion with telecommunication its so scaryyy man