Physics paper 1 - Discussion

[bamteck]

What about the question no. 2 smething about the graph at which the stone is falling?

I chose "C"

 

[Prince III]

What about the question no. 2 smething about the graph at which the stone is falling?

I chose "C"

the graph was like the below
it was ( C )

 

[Prince III]

i almost spent 15 minutes on the thermal expansion question

Thermal expansion is the tendency of matter to change in volume in response to a change in temperature. All materials have this tendency.

Option A
the resistance decreases in a filament lamp when is lighthened

this question also came in paper 2
the resistance also increases as the filament lamp is lighthened

OPTION B
the pressure in a close vessle increases as it is immersed into hot water
this option seems to be correct , because molecules of the gases gain energy , they collide more rapidly and hence the pressure increases , BUT there is a little problem there is NO THERMAL EXPANSION since the vessele was CLOSED

OPTION C
the fuse melts , when higher rating of current passes through them
this is wrong , this is not as a result of thermal expansion
this is result of heating the material to greater extent to it's specific heat capacity

OPTION D
the air above the bunsen burner rises as , it is lit up
Now when air is heated the volume of air increases means the air above the bunsen burner EXPANDS as the distance in their molecules increases , their density decreases as they rise UP
this is convection But please note that it is result of THERMAL EXPANSION !!


SO option D is correct

 

[kathuru_fani]

what was the answer for metal sphere and rod question?

and what two travels in air at same speed?

 

[Prince III]

what was the answer for metal sphere and rod question?

and what two travels in air at same speed?

at the end there were uniform positive charges on the metal sphere

gamma rays and there was another electromagnetic wave which both travel at the speed of light

 

[mimmi]

@prince III, even if the thing was closed it would expand won't it? Like if we heat a closed balloon it will expand? =S

 

[Prince III]

a ballon heated would burst beacuse the walls wount be able to hold the pressure inside the ballon , because molecules would collide at high speeds with the walls of the ballon
and i dont thnik particals of air would produce enough force to increase the volume of that vessele

 

[mimmi]

a ballon heated would burst beacuse the walls wount be able to hold the pressure inside the ballon , because molecules would collide at high speeds with the walls of the ballon
and i dont thnik particals of air would produce enough force to increase the volume of that vessele

I found this very interesting paragraph while searching

Gas Pressure Increase with Temperature
In 1702, Amontons discovered a linear increase of P with T for air, and found P to increase about 33% from the freezing point of water to the boiling point of water.
 
That is to say, he discovered that if a container of air were to be sealed at 0°C, at ordinary atmospheric pressure of 15 pounds per square inch, and then heated to 100°C but kept at the same volume, the air would now exert a pressure of about 20 pounds per square inch on the sides of the container.  (Of course, strictly speaking, the container will also have increased in size, that would lower the effect—but it’s a tiny correction, about ½% for copper, even less for steel and glass.)
 
Remarkably, Amontons discovered, if the gas were initially at a pressure of thirty pounds per square inch at 0°C, on heating to 100°C the pressure would go to about 40 pounds per square inch—so the percentage increase in pressure was the same for any initial pressure: on heating through 100°C, the pressure would always increase by about 33%.
 
Furthermore, the result turned out to be the same for different gases!

 

[Prince III]

hahahahaha i dont know what this all have to do with the question BUT answer is simply " D "

 

[Pals_1010]

@ mimmi

Yeah the statement B is correct in the sense that if it is put in boiling water, the molecules will gain energy and collide with an increased frequency and force the walls of the container, thus increasing pressure.

But it isn't the correct answer as the question asked about thermal expansion , i.e increase in volume due to heating effect, and statement B has nothing to do about volume.

Statement D is the right answer.

The air around the flame is warmed and and becomes less dense, as its volume increases while mass is constant. And thus it rises. This is a convection current.

 

[karthik]

NO ONE WOULD BELIEVE ME IF I SAY 23 QUESTION WERE REPEATED!!!!

Oh yeah?
Good for you then. Atleast you know that you have already got 23 marks.

As for me, i saw only 2 repeated questions. Lol. Well, I didn't even work out many past papers but this paper was relatively easy.

Check from 1968 to 1972 you will see many similar questions!! (different values)

 

[karthik]

I also got 6 days...but many friends said they g0t 4 days...!!!!

Ohh i feel sorry for ur friends LOL

 

[karthik]

How will they deflect into the page??

Young lady use the right arm rotation method

 

[karthik]

whats the answer for the resistance question that involves three resistors in parallel and three in series?

i might have lost a mark for that as i randomly picked the answer! the other question i lost a mark was that magnet electron question above!

i hould have revised :'(

when the three identical resisters where in series the total resistance was 6 ohms
means every fixed resister has a value of 2 ohms !

then when they were in parrallel we can use formula

1/ R = 1 / R1 + 1 /R2 + 1/R3

1/R = 1/2 +1/2 + 1/2
1/R = 3/2
R=2/3 ohms

(B) was the answer

LOL you could jst add the parrel resistors !!!

 

[karthik]

i answered when the air goes up when something is lit for thermal expansion. Stability is base area and centre of mass right?

Yeah I also selected that air is raising above a bunsen flame (option D) but some of my friends said that option B, about some pressure increasing was correct. Can u Help?
And Yes Stability depends on centre of mass and base area! that paper was insha allah very easy.

mmmm center of mass is choosen or fixed for every object .. it will not effect the stability ...... it the BASE area only

 

[karthik]

i almost spent 15 minutes on the thermal expansion question

Thermal expansion is the tendency of matter to change in volume in response to a change in temperature. All materials have this tendency.

Option A
the resistance decreases in a filament lamp when is lighthened

this question also came in paper 2
the resistance also increases as the filament lamp is lighthened

OPTION B
the pressure in a close vessle increases as it is immersed into hot water
this option seems to be correct , because molecules of the gases gain energy , they collide more rapidly and hence the pressure increases , BUT there is a little problem there is NO THERMAL EXPANSION since the vessele was CLOSED

OPTION C
the fuse melts , when higher rating of current passes through them
this is wrong , this is not as a result of thermal expansion
this is result of heating the material to greater extent to it's specific heat capacity

OPTION D
the air above the bunsen burner rises as , it is lit up
Now when air is heated the volume of air increases means the air above the bunsen burner EXPANDS as the distance in their molecules increases , their density decreases as they rise UP
this is convection But please note that it is result of THERMAL EXPANSION !!


SO option D is correct

Oh no the gas molecules rise is CONVECTION CURRENT NOT THERMAL EXPANSION AND THERMAL EXPANSOIN OCCURS ONLY IN SOLIDS GET IT !!!!!! SO THE RIGHT ANSWER IS B... students got lucky thinking gas movements but actually .... the molecules vibrate more in the container as they gain more energy resulting increase in pressure.......

 

[mimmi]

@ mimmi

Yeah the statement B is correct in the sense that if it is put in boiling water, the molecules will gain energy and collide with an increased frequency and force the walls of the container, thus increasing pressure.

But it isn't the correct answer as the question asked about thermal expansion , i.e increase in volume due to heating effect, and statement B has nothing to do about volume.

Statement D is the right answer.

The air around the flame is warmed and and becomes less dense, as its volume increases while mass is constant. And thus it rises. This is a convection current.

isnt it being put into boiling water?wont the container itself expand too?

 

[Prince III]

How will they deflect into the page??

Young lady use the right arm rotation method

NO!
you have to use the LEFT HAND RULE (FLEMMING LEFT HAND RULE)
But you are too lucky i guess , because if you use right hand rule and put the direction of middle finger in the direction of electrons you would get the right answer that was into the page

BUT

the correct method was to use left hand and put the middle finger opposite to the flow of electrons
that would point the thumb into the page

 

[Prince III]

mmmm center of mass is choosen or fixed for every object .. it will not effect the stability ...... it the BASE area only

the stabily depends / effects on both centre of the mass and the base area

 

[Prince III]

Oh no the gas molecules rise is CONVECTION CURRENT NOT THERMAL EXPANSION AND THERMAL EXPANSOIN OCCURS ONLY IN SOLIDS GET IT !!!!!! SO THE RIGHT ANSWER IS B... students got lucky thinking gas movements but actually .... the molecules vibrate more in the container as they gain more energy resulting increase in pressure.......

Thermal expansion is the tendency of matter to change in volume in response to a change in temperature. All materials have this tendency.


the above ^^ defination of THERMAL EXPANSION is written in WIKIPEDIA and many other books like fedrel and popel and explaing physics

altough that was convection but it is as a result of thermal expansion