physics paper 3, harder than hard

[kboss]

I got it using the formula, P=I2R. 0.75x0.75x 8.=4.5 W.

even if either one of our answers is wrong we can still get one mark for writing the formula correctly i believe...

 

[kboss]

What was the answer for the charge on the sphere after it was earthed?

everything become negatively charged...even the positive section becomes negatively charged

 

[Zeus]

Electrons flow from the Earth towards the metal sphere, not the other way around. =)

 

[kboss]

Electrons flow from the Earth towards the metal sphere, not the other way around. =)

yup!

 

[IGCSE O/L student]

THE PAPER WAS VERY FUNNY SO I SLEPT.
THE TEACHERS WERE ANGRY. IM PRETTY SURE THAT TEACHERS EVEN DIDNT KNOW THE ANSWERS.
THEN JOHN CENA CAME WITH A MIKE TO ME AND SAID THAT DO YOU SMELL WHAT THE ROCK IS COOKING. I ANSWERED THAT I AM DOING EXAM AND TO COME BACK LATER. WHEN I WOKE UP 3 TEACHERS WERE STARING ON ME AND THE INVIGILATOR SAID THAT 1 MINUTE IS LEFT. SO I THOUGHT WHAT THE HELL WILL I DO IN 1 MINUTE, SO I SLEPT AGAIN. THIS TIME I HAD DREAM OF OSAMA BINLADEN TELLING ME HE HIS KHAN AND HE IS NOT A TERRORRIST.ANYWAY INSHALLAH EVERYONE WILL GET "A" STAR (INSHALLAH). JUST STUDY WELL FOR PAPER6, I AM ABOUT TO SLEEP NOW BECAUSE 3 DAYS ARE LEFT.

u didnt do da ppr??

 

[IGCSE O/L student]

Electrons flow from the Earth towards the metal sphere, not the other way around. =)

it is da other way around coz u hv 2 chrge da sphere positively.

 

[RSDEV]

o my god i cant believe how hard that paper was. The paper was so twisted and hard that i actually ran out of time. I wasn't the only one.

I left a few questions to answer later on and when i finished my last question i ran out of time and never got time to attempt those questions. i left about 20 marks unattended.

Solving past papers didn't help at all. who else has finished this paper? how did you think the paper went, for me it went terrible.

For me it was alright .......But some questions were really confusing like finding the mass of the ice used. Bit time was not at all a problem with me. I finished 15 mins before the exam.

 

[IGCSE O/L student]

For me it was alright .......but some questions were really confusing like finding the mass of the ice used. Bit time was not at all a problem with me. i finished 11 mins before the exam.

i finished 25 minutes b4 da xam was supposed 2 b over

 

[Chucky]

efficiency is somewhere around 33 % not 25%

and the bird moves anti-clockwise, because after the additional force applied (when pulled) is not applied anymore when you let it go, the clockwise moment decreases and becomes equal to anti clockwise moment, an the bird rotates anticlockwise to return to equilibirum position.

 

[Chucky]

sorry man, 4.5 watts. :/ I took the time as one second.

that'sprobably correct too, i faintly remember seeing that as an answer.

 

[Chucky]

how many marks u expecting???
70??

expecting 65 to be lowest.
that's just over 80%

but don't worry, with the remarks i'm hearing from people, the scaling should be lower this time.

 

[Abhihsek]

you had to deduct background radiation like Chucky said.
the efficiency was something like 33%
the bulbs were 8 as a 5% increase in resistance per bulb will give you an 8.4 Ohm resistance.
If you divide 240V by 0.9 A , the total resistance is 266.67 which you then divide by 8.4 to give you the number of bulbs which are functioning at this current.
This comes to be 31.7, which rounds about to 32 bulbs. Thus 8 bulbs fail before a 0.9 A current is present in the circuit.

The bird one, I thought the centre of mass was above the pivot so I said it will go further clockwise thus as the centre of mass will cause a clockwise moment,
But when I realized ( after the paper) that the centre of mass was actually at the pivot itself, I understood that it will turn anti-clockwise to retain equilibrium.

But I still dont know how, can anyone please tell me the logic of it.

 

[Abhihsek]

The sphere will become negatively charged as the electrons from the earth will neutralise the positive charge but the electrons on the other side will remain attracted to the other sphere and will spread throughout the bigger sphere once the other sphere and the earthing is taken away

 

[Dandelion]

can anyone enlighten me if the negative charges on the sphere (the second one, with the wire connected to it) are DISTRIBUTED evenly or STAY CLOSED to the charged rod ?

 

[Daxter]

The power dissipated question wasn't in variant 2 and I got the bulb answer as 2...I used basic algebra..most of my class got it as 2

 

[St0cK]

unlucky i was even harder

yea i know !!! :'(

 

[Mesoud]

Not sure if this was brought up, but whatever.
In variant 1, there was a question about a bulb containing water at room temperature with a glass tube as the only opening upwards.
It was placed into warm water. The level of water in the glass tube decreased slightly then increased.

(a)Suggest why:
(i)the water level first fell
(ii)the water level then rose
(iii)the rise was greater than the fall

Any ideas about the answer? I'd really appreciate some help. The second one is pretty easy, but I'm not so sure about the first and third

 

[IGCSE O/L student]

Not sure if this was brought up, but whatever.
In variant 1, there was a question about a bulb containing water at room temperature with a glass tube as the only opening upwards.
It was placed into warm water. The level of water in the glass tube decreased slightly then increased.

(a)Suggest why:
(i)the water level first fell
(ii)the water level then rose
(iii)the rise was greater than the fall

Any ideas about the answer? I'd really appreciate some help. The second one is pretty easy, but I'm not so sure about the first and third

it was a glass flask
i)the flask expanded, and so the liquid fell
iii)liquids expand slightly more than solids do

 

[Triplet]

I thought the efficiency was somewhere around 25% since it's useful energy/total energy yes?

 

[aliqamar1995]

So what thresholds are you guys expecting lower or, are the gonna get high ?