Biology; Chemistry; Physics: Post your doubts here!

[TheStallion-Reborn]

(k) discuss the efficiency of energy conversions in common use, particularly those giving electrical output.
wht is meant by this point???

efficiency of wind turbines etc

 

[TheStallion-Reborn]

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_w12_qp_21.pdf
question 11 part b sub part 3, wont the oil droplet become neutral?/ the marking scheme says it would become negative. WHY?

 

[usama321]

(k) discuss the efficiency of energy conversions in common use, particularly those giving electrical output.
wht is meant by this point???

its usually the efficieny of a system. By efficiency it means the percentage of useful energy in a system. e-g an electric motor uses up 5000J, but the work done by it is of 4000J. The efficiency would be 4000/5000*100 = 80%

 

[usama321]

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_w12_qp_21.pdf
question 11 part b sub part 3, wont the oil droplet become neutral?/ the marking scheme says it would become negative. WHY?

yup i noticed that too while solving the paper. I think it might be due to the constant excess negative charge? Still this is no good answer, as the negative* charge should have been just pushed to the extreme end of the droplet

 

[Saad Mughal]

(k) discuss the efficiency of energy conversions in common use, particularly those giving electrical output.
wht is meant by this point???

You should know that systems that convert energy from one form to another are not 100% efficient.
In power stations (especially thermal power stations), the efficiency can be as low as 35%!
You should also know that in power stations, most energy is lost in the form of heat.

 

[Saad Mughal]

yup i noticed that too while solving the paper. I think it might be due to the constant excess negative charge? Still this is no good answer, as the positive charge should have been just pushed to the extreme end of the droplet

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_w12_qp_21.pdf
question 11 part b sub part 3, wont the oil droplet become neutral?/ the marking scheme says it would become negative. WHY?

The mark scheme is correct. While reading experiments, you guys might have came across the fact when charging a metal sphere, if you touch the sphere with the rod, the sphere gains the same charge as the rod (because of electron transfer).
Now, in this question, the top plate is negatively charged, this means that when the oil droplet touches it, it will gain electrons from the plate and become negatively charged.
Hope that helps you understand!

 

[usama321]

The mark scheme is correct. While reading experiments, you guys might have came across the fact when charging a metal sphere, if you touch the sphere with the rod, the sphere gains the same charge as the rod (because of electron transfer).
Now, in this question, the top plate is negatively charged, this means that when the oil droplet touches it, it will gain electrons from the plate and become negatively charged.
Hope that helps you understand!

of course the mark scheme is correct . Thanks for explaining it up, i was confused

 

[TheStallion-Reborn]

The mark scheme is correct. While reading experiments, you guys might have came across the fact when charging a metal sphere, if you touch the sphere with the rod, the sphere gains the same charge as the rod (because of electron transfer).
Now, in this question, the top plate is negatively charged, this means that when the oil droplet touches it, it will gain electrons from the plate and become negatively charged.
Hope that helps you understand!

GOD! man, u just CANNOT be an o levels student. go start giving lectures at UET!

 

[usama321]

The mark scheme is correct. While reading experiments, you guys might have came across the fact when charging a metal sphere, if you touch the sphere with the rod, the sphere gains the same charge as the rod (because of electron transfer).
Now, in this question, the top plate is negatively charged, this means that when the oil droplet touches it, it will gain electrons from the plate and become negatively charged.
Hope that helps you understand!

but what i still don't understand is why does it become charged so. I mean why does not it stop gaining electrons once the charge is balanced on it

 

[Saad Mughal]

of course the mark scheme is correct . Thanks for explaining it up, i was confused

I was just saying that because we've already found so many mistakes in the mark scheme.

 

[Saad Mughal]

but what i still don't understand is why does it become charged so. I mean why does not it stop gaining electrons once the charge is balanced on it

Because excess electrons are continuously flowing into it as long as it is connected to the plate! This is not the same as earthing, this is different, it will gain negative charge because of the excess electrons.

 

[Saad Mughal]

GOD! man, u just CANNOT be an o levels student. go start giving lectures at UET!

And here I wonder that will I even get an A* this year.

 

[usama321]

And here I wonder that will I even get an A* this year.

Oh you will get it inshallah

 

[Saad Mughal]

Oh you will get it inshallah

Insha Allah! Thanks

 

[TheStallion-Reborn]

And here I wonder that will I even get an A* this year.

idk if the mods are gona edit this now or not, but before they do, do read it. In punjabi, when someone says such a thing, like a praise worthy A* capable candidate doubting his grade, it's usually saud "KAR LAO GAL, TE SUN LAO BAAT" and thts exactly what came out of my mouth as soon as I read ur post

 

[Saad Mughal]

idk if the mods are gona edit this now or not, but before they do, do read it. In punjabi, when someone says such a thing, like a praise worthy A* capable candidate doubting his grade, it's usually saud "KAR LAO GAL, TE SUN LAO BAAT" and thts exactly what came out of my mouth as soon as I read ur post

I'm Punjabi. I know what you mean.
But yeah honestly. Some life experiences have thought me to not be over-confident for anything.

 

[AhsanAfzal]

conversiom to urdu= kal aao gey tou sun lo gey baat :/

 

[Saad Mughal]

conversiom to urdu= kal aao gey tou sun lo gey baat :/

No actually it translates to "Lo karlo baat aur sunlo iski baatayn" (I'm not too good at this frankly) .

 

[Hskk]

Physics, N12, region 1, paper 2 Q8bii.
ammeter reading: increases
voltmeter: decreases
Is that correct? The marking scheme says something like 'same as ammeter' then says 'both are correct' in brackets?

 

[TheStallion-Reborn]

Physics, N12, region 1, paper 2 Q8bii.
ammeter reading: increases
voltmeter: decreases
Is that correct? The marking scheme says something like 'same as ammeter' then says 'both are correct' in brackets?

no. the voltmeter also increases. because the voltage across thermistor decreases, (because the resistance decreases) so decrease in the pd across thermistor means increase in the voltage across the fixed resistor(the one across which is the voltmeter)