A2 Physics | Post your doubts here

[ambitious1]

Hey all,
Discuss your doubts on physics paper 5 here. As it will help you and others!

 

[candid24hours]

First things first: Dear Moderators,
I have been facing difficulty when it comes to finding A2 posts at the threads you have so kindly created for a more organized look. However, I wanted to see a separate thread for A2 questions and A2 questions alone. So, I came up with this thread.
Truth be told, A2 is very different from AS and the queries related to them are entirely different since there are different topics involved. I hope you understand.

My first A2 question: Can anybody please explain to me what 'infinite input impedance' means?

 

[smzimran]

First things first: Dear Moderators,
I have been facing difficulty when it comes to finding A2 posts at the threads you have so kindly created for a more organized look. However, I wanted to see a separate thread for A2 questions and A2 questions alone. So, I came up with this thread.
Truth be told, A2 is very different from AS and the queries related to them are entirely different since there are different topics involved. I hope you understand.

My first A2 question: Can anybody please explain to me what 'infinite input impedance' means?

Exactly, you are right!
About the question,
impedance means resistance!

 

[candid24hours]

Exactly, you are right!
About the question,
impedance means resistance!

In the book (Mike Crundle) they write: 'no current enters or leaves either of the inputs.'
When there is no current in the inputs, then there isn't any voltage right? (or am I missing something here? Do correct me if I am wrong.) So what would op-amp amplify?

 

[badrobot14]

First things first: Dear Moderators,
I have been facing difficulty when it comes to finding A2 posts at the threads you have so kindly created for a more organized look. However, I wanted to see a separate thread for A2 questions and A2 questions alone. So, I came up with this thread.
Truth be told, A2 is very different from AS and the queries related to them are entirely different since there are different topics involved. I hope you understand.

My first A2 question: Can anybody please explain to me what 'infinite input impedance' means?

Yes, what you say makes sense... anyways we'll let it stay till exams at least, inshaAllah...

 

[badrobot14]

First things first: Dear Moderators,

My first A2 question: Can anybody please explain to me what 'infinite input impedance' means?

look at your level you may say it's resistance... makes no difference..
When u came to uni level you find out that for AC resistance to Alternate current flow is of 2 types Reactance (due to inductors n capacitors) and resistance.... their combined magnitude is called Impedance...
(this is as far as I remember from my uni electronics course....)

 

[XPFMember]

Assalamoalaikum wr wb!
I got some doubts in June 2007 ....

· Q:3 d (i) Why is the answer zero? Just to confirm, is it because E=F/Q and F = ma so E is proportional to a...and hence a will be max. when E is max? is it?​

· Q:4 c (ii) How’ll the diagram be? :s​

· Q:7 b I don’t get why the damping is reduced...i took it as, resistance is increased, more power dissipated, hence more energy losses...so oscillations die off quicker..but it say damping is less..:s confused.. ​

· Q:7 c (iii) can you give some examples? ​

 

[hassam]

yea u r ryt abt 3 d(I)

 

[hassam]

yea question 7 b is important ....in shaping ur concept....this is how i resolved it
see e.m.f induced in the coil has nothing to do with resistance ryt...its depndent on no.of coils or speed of movement or things like that......so e.m.f induced will remain as 'V'......now if resistance is increased ...then current will decrease and we dont know by what factor so better not use I^2R....HERE U SHUD USE V^2/R SINCE V IS SAME BT R has increased so power loss will be less hence less damping

 

[hassam]

well as for the example of resonance...where is it useful...u can say in US ....and u knw from application part why we want resonance so as to get max amplitude of us waves....also in magnetic resonance imaging and NMR spectroscopy we use resonance....

 

[XPFMember]

yea u r ryt abt 3 d(I)

yeah thnx for the drawing..jazakAllah...actually, when I was doing this (drawing) question, dunno previously I had done it i drew it the other way, and when I saw it now, i felt it's wrong, so wanted a confirmation

yea question 7 b is important ....in shaping ur concept....this is how i resolved it
see e.m.f induced in the coil has nothing to do with resistance ryt...its depndent on no.of coils or speed of movement or things like that......so e.m.f induced will remain as 'V'......now if resistance is increased ...then current will decrease and we dont know by what factor so better not use I^2R....HERE U SHUD USE V^2/R SINCE V IS SAME BT R has increased so power loss will be less hence less damping

jazakAllah...i guess that makes sense

 

[XPFMember]

well as for the example of resonance...where is it useful...u can say in US ....and u knw from application part why we want resonance so as to get max amplitude of us waves....also in magnetic resonance imaging and NMR spectroscopy we use resonance....

so what exactly do I write?

 

[hassam]

yea...i guess smone else shud answer it ...i m not confident on it ....i just knw how to name these examples.....

 

[hassam]

brothe r for question 7 part B i got amore convincing explanation.....and THATS THE REAL EXPLANATION I think....see the current induced in coil will poroduce an opposing magnetic field which will produce the damping force...so when reistance increased ....current less so opposing magnetic field in the coil small so as a result less damping.....i guess now ur concept wud be clear....thnx for mbringing this question into my attention

 

[XPFMember]

brothe r for question 7 part B i got amore convincing explanation.....and THATS THE REAL EXPLANATION I think....see the current induced in coil will poroduce an opposing magnetic field which will produce the damping force...so when reistance increased ....current less so opposing magnetic field in the coil small so as a result less damping.....i guess now ur concept wud be clear....thnx for mbringing this question into my attention

ohh....my teacher was trying to explain something abt this (back emf) but I couldn't understand it...
can you explain me a bit more...plz

 

[hassam]

sea when the e.m.f is induced in the coil....a current will flow in that circuit....since thee is a coil with current in it ....it will produce a magnetic field that will oppose the motion of magnet according to lenz's law....so when R increased I DEcreased so opposing B decreased.....so as a result less damping....feel free to ask if u dint understand

 

[XPFMember]

sea when the e.m.f is induced in the coil....a current will flow in that circuit....since thee is a coil with current in it ....it will produce a magnetic field that will oppose the motion of magnet according to lenz's law....so when R increased I DEcreased so opposing B decreased.....so as a result less damping....feel free to ask if u dint understand

ok now i understand this...
but see part a....in that it asks the reason for damping...
i'm getting confused with all this

 

[smzimran]

Yes, what you say makes sense... anyways we'll let it stay till exams at least, inshaAllah...

Aoa,
We need two more threads for A2 mathematics and A2 chemistry, should i start them ?

 

[hassam]

yea.........that is also alright...........k i have offered u two explanations....u cn stick with the one that seems reasonable to u

 

[XPFMember]

yea.........that is also alright...........k i have offered u two explanations....u cn stick with the one that seems reasonable to u

Assalamoalaikum wr wb!
but mind explaining me the other way...? plz...
I wanna know about that..