Physics, Chemistry and Biology: Post your doubts here!

[Silver Wing]

If I lost up to 15 marks in my chemistry exam, is it still an A* ?

 

[ThatReallyReallyWeirdDude]

help Q5di http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Physics (0625)/0625_s10_qp_31.pdf

Power is given as 2kW = 2000watts
Energy = Power x Time
Time is 4 minutes (22-18) = 4x60=240 seconds
Energy = 2000 (power) x 240 (time) = 480,000J or 480kJ

 

[ThatReallyReallyWeirdDude]

If I lost up to 15 marks in my chemistry exam, is it still an A* ?

Depends on grade threshold
There have been exams where threshold is less than 45/60 but that's rare, it's usually 47-50/60. Maximum was 54/60
It depends how hard the paper was and how many people score low (that's how they choose grade, by plotting it on curve and stuff).
Last year variant 1 A* was 40/60
Just try hard to study for paper 1 and 3 and you can make up for it and inshallah get an A* Paper 6 is only 20% out of 100, so losing 15 marks is only a loss of 5%; you still have a chance.

 

[AAnsarii]

No, i dun thnk i even heard about it but u have to learn for alkenes (bromine n all) =]

thnx

 

[Babs saad]

someone please help me with dc motor, i dont understand it

 

[kainat husain]

View attachment 10679

Alright
It says that it JUST tips the scale; that means its JUST above equilibrium
So we can assume clockwise moments = anticlockwise moments
so moment caused by man = moment caused by planks weight
so 0.17xW = 0.78x160
W=(0.78x160)/0.17=734N.
That's what the mark scheme says

but y did u take 0.17? and 0.78 istead 0.20 and 0.75

 

[ThatReallyReallyWeirdDude]

but y did u take 0.17? and 0.78 istead 0.20 and 0.75

Because the pivot is not at the center of P, it's on the left corner
The distance between W and the center of P is 0.2 - so you have to take away the distance between the center of P and it's corner, which is 0.06/2 = 0.03
On the other hand the distance between the weight and the center of P is 0.75 - however, we need the distance between the weight of the plank and the left corner so we add 0.03

 

[ThatReallyReallyWeirdDude]

someone please help me with dc motor, i dont understand it

http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/motdc.html

 

[Moi]

Can someone please explain to me how the generator and motor work ?? and the whole commutator and slip/split rings thigy !! PLEASE HELP

 

[ThatReallyReallyWeirdDude]

http://www.wisc-online.com/objects/ViewObject.aspx?ID=IAU13208

Can someone please explain to me how the generator and motor work ?? and the whole commutator and slip/split rings thigy !! PLEASE HELP

Very awesome. Try it!

 

[sadiaali]

Please explain the right hand grip rule and fleming left hand rule

 

[MERIHAN]

View attachment 10678
You're supposed to use a compass to draw the three waves again centered around R. You shouldn't include the bit behind the solid barrier - that is the faded red lines on the diagram I made for you, but that's so you can understand.

how you took R ?? IS IT BY TAKING EQUAL DISTANCE FROM THE REFLECTING SURFACE ???

 

[ThatReallyReallyWeirdDude]

how you took R ?? IS IT BY TAKING EQUAL DISTANCE FROM THE REFLECTING SURFACE ???

Yes

 

[MERIHAN]

Yes

THNX SOOO MUCH ......

 

[ThatReallyReallyWeirdDude]

Please explain the right hand grip rule and fleming left hand rule

Left hand rule:

So as long as you know two of them, you can find the other.
E.g. if you know magnetic field and direction of current, just put your fingers in those directions and however you have to twist your hand to do so will show direction with thumb
Right Hand grip Rule:
There's two, one is for a current carrying wire, where the fingers show the direction of the field:

The other is for a solenoid, where you put your fingers in the direction of the current and the thumb shows the north pole:

 

[sadiaali]

Left hand rule:

So as long as you know two of them, you can find the other.
E.g. if you know magnetic field and direction of current, just put your fingers in those directions and however you have to twist your hand to do so will show direction with thumb
Right Hand grip Rule:
There's two, one is for a current carrying wire, where the fingers show the direction of the field:

The other is for a solenoid, where you put your fingers in the direction of the current and the thumb shows the north pole:

Thank you sooooooooooooooooooooo much !!!!!!!!!

 

[za Shadow]

PLZ HEEEEELLPP

http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Physics (0625)/0625_w08_qp_03.pdf
http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Physics (0625)/0625_w08_ms_3.pdf
q 1 d ii) my answer was 0.72 but it was wrong although i used speed=dist/time the correct answer was 0.36 WHYYYY why did u divide by 2??????????

q 5 c) how do we get the answer????? WE SHOULD ADD THE MINUTES (4) AND ADD THE MASSES why did we subtract 16.3 - 2.1 and why did we use 2 minutes not 4 minutes?????? plzzzzz help me

 

[Moi]

http://www.wisc-online.com/objects/ViewObject.aspx?ID=IAU13208


Very awesome. Try it!

OMG thank you soooo much !! Now i got the whole thing and understood it !! Thx soo much.. any link for how the AC Generator work ?? Thx again so much

 

[thats_me]

PLZ HEEEEELLPP

http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Physics (0625)/0625_w08_qp_03.pdf
http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Physics (0625)/0625_w08_ms_3.pdf
q 1 d ii) my answer was 0.72 but it was wrong although i used speed=dist/time the correct answer was 0.36 WHYYYY why did u divide by 2??????????

q 5 c) how do we get the answer????? WE SHOULD ADD THE MINUTES (4) AND ADD THE MASSES why did we subtract 16.3 - 2.1 and why did we use 2 minutes not 4 minutes?????? plzzzzz help me

Q1 d ii wat did u use for speed?

 

[za Shadow]

Q1 d ii wat did u use for speed?

0.6 and then i multiplied it by 1.2 (time)