Physics P4 Discussion

[rahultaneja2010]

How much UMS would 85/100 be in this paper ? Because I'm aiming for a* and scored 86 UMS for AS .... Pls help

 

[h.b]

but the graph was not sinosudioal it is rectangular..

why was it inverted and rectangular=S

 

[OakMoon!]

why was it inverted and rectangular=S

Firstly, Vout is calculated by multiplying, (V+ - V-) with gain. Since, the input was connected to V- and V+ was at 0 potential the graph had to be inverted. Secondly, all the values of Vout will be saturated as the op amp was ideal and so it had an infinite open loop gain.

 

[rahultaneja2010]

Pls help me answer my question !!!

 

[extremeranger]

the variation in the mass for the magnetic question was +1.0g / -1.0g i think....caz u had to find the peak current from the rms then find the total change in mass which was around 4.6 and then the variation which was 4.6-3.6 = 1.0g caz 3.6 was the original reading when no current was flowing so yeaa...

 

[extremeranger]

and how did u guys find the electric field strength from that gradient question

 

[Gooners]

Firstly, Vout is calculated by multiplying, (V+ - V-) with gain. Since, the input was connected to V- and V+ was at 0 potential the graph had to be inverted. Secondly, all the values of Vout will be saturated as the op amp was ideal and so it had an infinite open loop gain.

So u say tht the inverted graph had amplitude of 5V ?

 

[Mustehssun Iqbal]

I calculated 2 cm oscillations and then cancelled it and wrote 1 cm due to new working. That's called the disadvantage of over- smartness
I'll get a C1 mark if there's any though, or M1 InshAllah.

 

[OakMoon!]

So u say tht the inverted graph had amplitude of 5V ?

I posted a picture of the answer on the last page of this thread. Check it out.

 

[h.b]

Firstly, Vout is calculated by multiplying, (V+ - V-) with gain. Since, the input was connected to V- and V+ was at 0 potential the graph had to be inverted. Secondly, all the values of Vout will be saturated as the op amp was ideal and so it had an infinite open loop gain.

ofcourse!!!! thanks....man im doomed.....lost 30 marks......how will i ever get an A now=''''[

 

[extremeranger]

omg i felt so intelligent just understanding the rectangular part of the graph part i didnt even care to see if it would be inverted

 

[h.b]

omg i felt so intelligent just understanding the rectangular part of the graph part i didnt even care to see if it would be inverted

lol u will still score 2/3

 

[Hussain Mir@lhr]

asalamulaikum
my p4 was horrible i think il just get 42 ..can some one plz tell me if it is possible to score a B over all if u get tht much in p4...plus can someone explain how exactly the overall grade is calculated using an example ?

 

[aaditya menon]

The Vout graph was something like this:

View attachment 9690

That's correct!

Okay, I have a doubt here. The change in gravitational potential energy of the moon when the radius of the orbit increases by 4cm?

I was getting an answer almost 0, so close even the calculator didnt show the change. I wrote 0J for that, what did you guyz get? How do you really go about solving that?

 

[OakMoon!]

That's correct!

Okay, I have a doubt here. The change in gravitational potential energy of the moon when the radius of the orbit increases by 4cm?

I was getting an answer almost 0, so close even the calculator didnt show the change. I wrote 0J for that, what did you guyz get? How do you really go about solving that?

You just had to multiply the above force of attraction with .04. So you got something in 10^18. The method you implied was not correct. And even if it was small you should have written the answer in index form, 10^-12 e.tc.

 

[aaditya menon]

You just had to multiply the above force of attraction with .04. So you got something in 10^18. The method you implied was not correct. And even if it was small you should have written the answer in index form, 10^-12 e.tc.

damn, so you're saying the change in gp is somthing 10^18? Whoa, how is that practically possible when the radius changes by 4 cm?!?!

 

[OakMoon!]

damn, so you're saying the change in gp is somthing 10^18? Whoa, how is that practically possible when the radius changes by 4 cm?!?!

Is it? Remember that you are overcoming a force of attraction that is as large as 10^20. So you need to do large amount of work to increase the radius by even 4cm.

 

[aaditya menon]

Is it? Remember that you are overcoming a force of attraction that is as large as 10^20. So you need to do large amount of work to increase the radius by even 4cm.

Well, makes sense. I still don't get how W = Fd can fetch u 3 marks.
And why is using the GPE formula for the moon incorrect here?

 

[OakMoon!]

Well, makes sense. I still don't get how W = Fd can fetch u 3 marks.
And why is using the GPE formula for the moon incorrect here?

Were you able to identify that you needed to use F*change in r? NO! So that means the three marks were justified. Many people were unable to do so. What is GPE formula? Change in potential times m. Change in potential is due to the change in r. And remember that F=Gmm/r², if you multiply this by r, you get Gmm/r which is the formula for GPE. Anyways, I couldn't also believe how could they give such a simple thing for 3 marks. But now I realize that identification of the formula was the most important part of this question.

 

[histephenson007]

omg i felt so intelligent just understanding the rectangular part of the graph part i didnt even care to see if it would be inverted

I know, I did the same thing!!!!!