A2 Physics | Post your doubts here

[hassam]

which one...power one or this back emf one

 

[XPFMember]

which one...power one or this back emf one

back emf one..

 

[candid24hours]

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

Thankyou so much. =>

 

[smzimran]

Assalamoalaikum wr wb!!

PAPER 4 doubts...

Nov 2002

· Q:3 b(ii)​

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P.S. A2 doubts to be shifted here..So post the answers in that thread..​

Jazak Allahu Khairen..​

Aoa,
These short impulsive forces are like push given to a child on a swing each time the swing returns to you,
Their effect: increase amplitude of oscillation!
Hope you understood!
P.S : Post that question box here!

 

[XPFMember]

Assalamoalaikum wr wb!!

PAPER 4 doubts...

June 2002

· Q:4 b & c​

· Q:6a how should we draw that...? :s​

Nov 2002

· Q:3 b(ii)​

Nov 2003

· Q:5 b (ii) need explanation, I don’t get it... :s​

· Q:4 c Can you show, how is the less ripple represented, please.. :s​

· Q:2 b (ii) –ve sign?​

June 2004

· Q:4 c reason for the answer...​

· Q:6 last part..​

· Q:8 iii who said we didn’t use them? :s​

​

June 2005

· Q:5b​

· Q:6b​

Nov 2005

· Q:3 I’m sorta confused with the calculation...part b ...and I don’t understand why they give the ans to C to 2s.f when they’re penalising 2s.f in part b?​

· Q:4 c Why speed max when displacement is zero? :s​

· Q:5b(ii) why when speed is reduced, deflection is larger? :s​

· Q:6 b I don’t understand​

·Q:6 c (ii) which way do we do...negative of the upper graph gradient? ​

June 2006

· Q:2 b (ii) how to do?? :s​

· Q:4 c can you show, plz?​

· Q:6 a what I understand is the field should be circle..right? I don’t get this :s​

· Q:6 c what do I write for this?​

· Q:7 Can you answer the complete question, I couldn’t do this one... ​

· Q:8 a For such questions where exactly are we supposed to draw the arrow? Like beside the paper shown..or inside that region? Where do we show....?​

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Nov 2006

· Q:3 c what to write? :s​

· Q:4 b ans. Is 5.99 x 10^24 how does ms say 6.00 :s​

· Q:5 a (ii) what’s eddy current?​

· Q:6 a (ii) How do the diode works then, normally...isn’t that the way we usually connect? :s​

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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 dissioated, 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? :s​

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I'm sorry for so many doubts, but please can you answer them by few at a time..​

​

P.S. A2 doubts to be shifted here..So post the answers in that thread..​

Jazak Allahu Khairen..​

 

[unique840]

June 2004

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· Q:6 I’m totally blank abt this...i don’t get how they worked this out..​

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june 2004 q6) a)constant temp means no change in internal energy. gas is being compressed so work is done on the gas.
according to the equation U = q+w
change in internal energy is zero. work done is increased so "q" is decreased
b) no expansion means constant volume. so work done is zero. change in internal will increase and so will change in "q"
sorry i dun knw the last part

 

[unique840]

June 2004

· Q:8 iii who said we didn’t use them? :s​

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june 04 q8) the binding energies of uranium barium and krypton are used. we didnt use neutron's binding energy because neutron is a single particle and it does not have any binding energy

 

[unique840]

Nov 2005

​

·Q:6 c (ii) which way do we do...negative of the upper graph gradient? ​

June 2006

· Q:8 a For such questions where exactly are we supposed to draw the arrow? Like beside the paper shown..or inside that region? Where do we show....?​

​

nov 05) yup u will do it lyk dis. negative of the upper graph gradient.
june 2006 q8a) inside the region

 

[smzimran]

Assalamoalaikum wr wb!!

PAPER 4 doubts...

​

Nov 2006

· Q:3 c what to write? :s​

· Q:4 b ans. Is 5.99 x 10^24 how does ms say 6.00 :s​

· Q:5 a (ii) what’s eddy current?​

· Q:6 a (ii) How do the diode works then, normally...isn’t that the way we usually connect? :s​

​

​

P.S. A2 doubts to be shifted here..So post the answers in that thread..​

Jazak Allahu Khairen..​

Q3(c)
We just need to cause damping to make the peak flatter (i.e decrease amplitude!)
A suggestion regarging introduction of damping like immersion in liquid would do!

Q4(b)
Yes ans is 5.99 x 10^24 but that answer comes if you use the values stored in ur calculator after each step,
if you round the values after each step, just like the m.s does, u will get 6.00 * 10^24 !

Q5(a)(ii)
http://www.xtremepapers.com/revision/a-level/physics/electromagnetic_induction.php
Scroll down!

Q6(a)(ii)
When diode receives V = 8.48 V that is the peak voltage meaning all voltage is received by the diode, and thereby resistor receives no p.d

 

[smartangel]

i have a query in Q 12 b (ii). see to get the total no of amplifiers we divide 125 by 6. that gives us 20.8 which should be rounded off to 21 hence total gain should be 21 x 23.. in the marking scheme they hav rounded it off to 20 thus a huge difference in the answers. is there any explanation for them rounding off 20.8 to 20??
http://www.xtremepapers.com/papers/...and AS Level/Physics (9702)/9702_s09_qp_4.pdf

 

[smzimran]

i have a query in Q 12 b (ii). see to get the total no of amplifiers we divide 125 by 6. that gives us 20.8 which should be rounded off to 21 hence total gain should be 21 x 23.. in the marking scheme they hav rounded it off to 20 thus a huge difference in the answers. is there any explanation for them rounding off 20.8 to 20??
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s09_qp_4.pdf

Aoa,
Its common sense dear, how can 20.8 be rounded off to 21 ? Its not some maths quantity, its number of amplifiers,
Its rounded to 20 because 20.8 makes it 20 amplifiers and not the complete 21st so there must be some extra length of cable!
0.8 is like the remainder!
An example:
If you are to divide 5 cakes among 4 children, what do you do?
Ans: You give one to each kid and 1 cake is left as remainder!
I hope you understood

 

[smartangel]

Aoa,
Its common sense dear, how can 20.8 be rounded off to 21 ? Its not some maths quantity, its number of amplifiers,
Its rounded to 20 because 20.8 makes it 20 amplifiers and not the complete 21st so there must be some extra length of cable!
0.8 is like the remainder!
An example:
If you are to divide 5 cakes among 4 children, what do you do?
Ans: You give one to each kid and 1 cake is left as remainder!
I hope you understood

haha right! now i get it.. thanks

 

[smartangel]

in Q10..for V-.. why do we divide 2000 by 4100.. why not the resistance of the thermistor .ie 2100 divded by 4100?
http://www.xtremepapers.com/papers/...nd AS Level/Physics (9702)/9702_w09_qp_41.pdf

 

[XPFMember]

Assalamoalaikum wr wb!
Nov 2007

• Q:1b(i) I don’t understand how to do this..i did see the mark scheme but still I wanna know why to do this..or how to arrive at this..:s
• Q:4 b need explanation + how to draw..?
• Q:4 c (ii)I don’t understand, can someone plz explain me..
• Q:4 d explanation... :s
• Q:5 b (ii) Which area do I determine...

 

[smartangel]

this question is from the cie coursebook..please explain b (ii)

A strain gauge contains 15 cm of wire of resistivity 5.0 × 10−7 Ω m. The resistance of the
strain gauge is 150 Ω.
i Calculate the cross-sectional area of the wire in the strain gauge. [2]
ii Calculate the increase in resistance when the wire extends by 0.1 cm, assuming that
the cross-sectional area and resistivity remain constant.


the answer to b (ii) is Extends by 1/150 so resistance increases by a factor of 1/150 , which is 1 Ω.

 

[Mustehssun Iqbal]

this question is from the cie coursebook..please explain b (ii)

A strain gauge contains 15 cm of wire of resistivity 5.0 × 10−7 Ω m. The resistance of the
strain gauge is 150 Ω.
i Calculate the cross-sectional area of the wire in the strain gauge. [2]
ii Calculate the increase in resistance when the wire extends by 0.1 cm, assuming that
the cross-sectional area and resistivity remain constant.


the answer to b (ii) is Extends by 1/150 so resistance increases by a factor of 1/150 , which is 1 Ω.

Assalamu alaikum,
Calculation is done, but I don't completely understand the explanation given in the marking scheme. It got calculated the other way, I guess. Method is different but the answer is same. Do you want me to post the solution??

 

[XPFMember]

Assalamoalaikum wr wb!
For application part, in inverting amplifier...it says input impedance is infinite so current in R(in) is equal to the current in R(f)
I dont get why? can someone plz explain this? :s

 

[XPFMember]

Assalamoalaikum wr wb!!
reposting the ones left
JazakAllah khairen for solving the other ones..many duas 4 all....

PAPER 4 doubts...

​

Nov 2003

· Q:4 c Can you show, how is the less ripple represented, please.. :s​

​

June 2004

· Q:4 c reason for the answer...​

· Q:6 last part..​

· Q:8 iii who said we didn’t use them? :s​

​

​

June 2006

· Q:2 b (ii) how to do?? :s​

​

· Q:6 c what do I write for this?

· Q:7 Can you answer the complete question, I couldn’t do this one... ​

​

​

Nov 2006

· Q:3 c what to write? :s​

· Q:6 a (ii) How do the diode works then, normally...isn’t that the way we usually connect? :s​

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 dissioated, 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? :s​

​

Nov 2007

• Q:1b(i) I don’t understand how to do this..i did see the mark scheme but still I wanna know why to do this..or how to arrive at this..:s
• Q:4 b need explanation + how to draw..?
• Q:4 c (ii)I don’t understand, can someone plz explain me..
• Q:4 d explanation... :s
• Q:5 b (ii) Which area do I determine...

 

[XPFMember]

Nov 2006
Q6(a)(ii)
When diode receives V = 8.48 V that is the peak voltage meaning all voltage is received by the diode, and thereby resistor receives no p.d

but then in other cases, when we use a diode how do we connect it? :s isnt it the same way?

 

[smzimran]

but then in other cases, when we use a diode how do we connect it? :s isnt it the same way?

Aoa,
We connect it the same way but the diode then has low resistance and R has larger, so p.d across R is way more than that of diode!