A2 Physics | Post your doubts here

[Abdulrab]

With the application booklet I got some main ideas and then got to understand everything much better through answering past papers and then checking the mark-schemes...

ok

 

[hassam]

then dude just memorise the markschemes.......its also much easier to understand from there rather than taking the pain to read from booklet

 

[hassam]

well why newtons law apply to planets even though they r nt point masses......ms says radius much smaller than separation.........i dint unerstand this....wen performing calculations we are taking distance between centres of two planets.......isnt it?

 

[hassam]

hoow limiting aperture size improves sharpness and how backing photgraphic film with flourescent material improves contrast

 

[mybch]

oct/nov 2006 question 5(b)
could anyone please explain this for me ?

 

[miss irfan]

can somebody explain june 2011/paper 41 Q5 c i and ii?
https://docs.google.com/viewer?a=v&...gg4Ogp&sig=AHIEtbSbGoVeDuDsOfaeUGuKyfZmUNnesg

 

[ousamah112]

oct/nov 2006 question 5(b)
could anyone please explain this for me ?

Oscillations are damped by eddy currents. These currents dissipate energy in the form of heat to surrounding as E=IVt. energy comes from the oscillations of the system. As, energy is lost gradually, amplitude also decreases gradually because amplitude depends on energy...

 

[ousamah112]

well why newtons law apply to planets even though they r nt point masses......ms says radius much smaller than separation.........i dint unerstand this....wen performing calculations we are taking distance between centres of two planets.......isnt it?

because we assume that planets are of uniform density and its mass is concentrated at its centre. (i am not sure though_

 

[ousamah112]

ok

read applications from International A/As level Physics by hodder education. Writers: Chris Mee,mike crundell

 

[mybch]

thanks a lot
and yes i will surely pray for your exams
pray for mine too

 

[mybch]

I have another doubt
please explain if you dont mind
June 2004 question 5 d (i) and (ii)
Why is the r.m.s value the same?

 

[miss irfan]

please answer my question too

 

[hassam]

Suggest why a patient may be asked to hold his
or her breath during a CAT sean.

 

[mybch]

please answer my question too

5c(i)
the reason the direction is from bottom to top is because that is the only direction of current that the magnetic field satisfies ( you can find this out with left-hand rule )
5 c (ii)
Bqv = mv^2/r
(Bq) r = mv = momentum
therefore radius is proportional to momentum of the particle
since kinetic energy before passing through foil is more than after passing through the foil , the radius before passing through foil is smaller
therefore (5.7/7.4) = 0.77

 

[hassam]

SUUGEST WHY ULTRASOUND CANT BE USED TO EXAMINE BONES
ultrasound isn't used to image bones. you get plenty of reflection of the ultrasound energy at the tissue/bone interface, but very little transmission into the bone. That means there's little to no sound energy reflecting back from any boundaries within the bone for the transducer to detect. WELL ONE confusion we can i guess get the image of outline of bone isnt it cos we will be recieving the reflection from bone/.....it is only reflection from the other side of bone we ll not get ......so why we dont use it o examine deformities in bone

 

[miss irfan]

what value of voltage do we use while calculating the mean power through a resistor. the rms value or the peak value and why?

 

[hassam]

when e

what value of voltage do we use while calculating the mean power through a resistor. the rms value or the peak value and why?

ver u see mean power....use RMS values

 

[ousamah112]

I have another doubt
please explain if you dont mind
June 2004 question 5 d (i) and (ii)
Why is the r.m.s value the same?

because that Irms=Io/2^1/2 is only applicable to sine curve waves as it was derived from I=Iosinwt.

 

[ousamah112]

I have another doubt
please explain if you dont mind
June 2004 question 5 d (i) and (ii)
Why is the r.m.s value the same?

for square Irms= peak value and for sawtooth Irms=Io/3^1/2

 

[hassam]

The ultrasound image
clearly shows the baby's skin and some bones.
Explain why these show up clearly while softer
organs inside its body do not.