Physics paper3: the discussion.

[Ivo]

The question about what was assumed (when calculating speed of sound) and why was storm never passed directly overhead was also hard qs for me.

assumption was asked in one the pastpapers but i forgot it i think it was speed of light is negligible,i wrote a big paragraph for that one mark as i wasnt sure exactly whats the ans.!
and ffor that storm never passed i guess i wrote the time decreases till (dont remember the value ) and again starts to increase so always takes some time to reach!

Oh, I said there was no time when the interval was 0, therefore storm didn't pass overhead. I was dumb and put assumption as speed of sound is constant!

 

[XPFMember]

no idea!

 

[Ivo]

How about for the last question, it asked for resistance and power loss? What was the answers for those?

 

[XPFMember]

Resistance was to be found using the formula V/I and Power using VXI,i dont remember the answers!

 

[Ahmedattia24]

How about the fill in the blank part involving the length and resistance of the wire?

I found this exam really hard, what does everyone think?

 

[XPFMember]

exam was easy except few question that blank was =>" 3/8 times " ,i am talking abt variant 1!

 

[Ivo]

How about the fill in the blank part involving the length and resistance of the wire?

I found this exam really hard, what does everyone think?

Oh yeah, filling in the blank, were we meant to write a numerical answer. That was so hard!

 

[Ivo]

exam was easy except few question that blank was =>" 3/8 times " ,i am talking abt variant 1!

Pleae explain how you got the answer.

 

[omarko]

exam was easy except few question that blank was =>" 3/8 times " ,i am talking abt variant 1!

Pleae explain how you got the answer.

The resistance in the first part of the question was 4 Ohm
Now the question said that half the diameter of the same wire was used which was supposed to give 4R= 16 Ohm
Instead u got 6 Ohm when u calculate the new values
Which means that resistance went down in relation to length.so, the length must have gone down.
If you divide 6/16 the result is 3/8.

 

[XPFMember]

i used a formula which i saw in the book but it wasnt there in our syllabus as i wasnt getting it to do in any other way=> Resistance = constant X length/diameter. let the diameter and length of first one be " 1 " find the const by rearranging it will be 8.now for the 2nd wire find the resistance using V/I .i think it is 6. now rearrange the eqn to find its length=> length=resistance X diameter/cons. = 6 X 0.5 / 8 = 3/8
we will take diameter as 0.5 cuz its half the original

 

[shawkat]

but i write the speed 333.3

 

[XPFMember]

but i write the speed 333.3

yeah we said that speed is 333.3 ,what do u mean to say???

 

[Ivo]

OK, how about for the question about cars, the one about why power conversation is greater or something.

And also, for the question about latent heat, for 2 marks, did it ask for energy changes of latent heat of vaporisation?

And also, what was the water level changes and how did you explain it?

 

[XPFMember]

i remember the car question but not the conservation or something
latent heat ,yes they asked energy change of vaporization
and water level i already said

but i wrote that the level in the matt black bulb will go up since it absorbs heat and expands so volume increases and pressure decreases!And since that shiny one is a bad absorber there wouldnt be any change in that one!!

but now i think for the shiny one it should decrease cuz if it rise in one it will fall in the other!

 

[Ivo]

i remember the car question but not the conservation or something
latent heat ,yes they asked energy change of vaporization
and water level i already said

but i wrote that the level in the matt black bulb will go up since it absorbs heat and expands so volume increases and pressure decreases!And since that shiny one is a bad absorber there wouldnt be any change in that one!!

but now i think for the shiny one it should decrease cuz if it rise in one it will fall in the other!

For that, I think higher temp. at black side, constant pressure, so air expands, so increases volume, pushes water level down, consequently water level at white side goes up, cos it's cooler that end.

I'm just not sure if it's to do with pressure increase or volume increase

 

[XPFMember]

i have no idea better we leave it for the examiner to decide

 

[Ahmedattia24]

This question is clearly e.c.f
The explanation should be suitable to the mark you made on the figure.

 

[Ahmedattia24]

I also made the fill in the blanks half, without calculation. Here is why:

The first answer was 4, they said the diameter halved, that means the resistance should now be 8, but it came out to be 6, that means the length decreased, they gave space for a single answer, so I wrote half without thinking much.

 

[Ivo]

I also made the fill in the blanks half, without calculation. Here is why:

The first answer was 4, they said the diameter halved, that means the resistance should now be 8, but it came out to be 6, that means the length decreased, they gave space for a single answer, so I wrote half without thinking much.

However, the factor of increase for the resistance is different for diameter and area.

 

[whoopiesh]

paper 3 physics was quiet terrible!!!! i almost left 100 points blank!!!!!!!!!!!