Biology; Chemistry; Physics: Post your doubts here!

[adilahmed900]

Hi guys.
Can some one help me out here?
I didn't take any tuition of Biology, Chemistry and Physics.
Now I am having trouble, where should I study all the lab experiments and investigations from which are in the GCE O level course????
Like the colour changes etc? Can any one help me out please? Should I just do the ATP papers? OR is there any specific place where there are notes to study for chemistry biology physics colour changes, lab activities and investigations?? HELP HELP ??

 

[ashiqbal]

i am solving this on my own
Q1(i) diode
(ii) to prevent any current flowing into transistor. as such a large current could damage transistor
b(i) 6*2000/(5000+2000) =1.7 volts
b(ii) as the light intensity increases on LDR its resistance decreases this would increase the voltage across the resistor 2. Not gate would recognize this as "1" and convert it into "0" i.e current will not flow at the resistor. and as the transistor detects no current at its base so it would not switch on the collector emitter current. so the relay wont be switched on and thus bulbs wont light.
Q2a(i) transistor
Q2a(ii) increases and does not affect
Q2a(iii) this circuit could be used in green house.
Q3a when the sensor gets wet its resistance decreases the current flows in base of transistor. transistor switches on the collector emitter current and so bulbs would light.
b(i) in order to make no electrical connection between the two ciruits. the link is mechanical and magnetic. preventing any harm to the ciruit operating at low voltage.
b(ii) decreasing its voltage would switch on the circuit while increasing its voltage would switch off the ciruit.
Q4 a(i) this limits the amount of current flowing into the transistor to avoid damaging it.
ii(A) Water provides a conducting path for the probes.voltage at the base reaches 0.7 volts and the this switches on the transistor
ii(B) Transistor allows a large current to flow from collector to emitter. current flowing through relay creates the magnetic field which attracts the lever and allows current to flow in the buzzer which then sounds.
iii it can be used for warning of rain

thanks, i will check and reply if that is alright or not

 

[Spidey21]

Hi guys.
Can some one help me out here?
I didn't take any tuition of Biology, Chemistry and Physics.
Now I am having trouble, where should I study all the lab experiments and investigations from which are in the GCE O level course????
Like the colour changes etc? Can any one help me out please? Should I just do the ATP papers? OR is there any specific place where there are notes to study for chemistry biology physics colour changes, lab activities and investigations?? HELP HELP ??

well...i think you should study from the past papers...try to solve them..and in case you dont get it ask away!!

 

[RaneemI]

Can anyone plz explain the mechanism of how the van de graaff generator work in , & it would be better if pictures are included to make it simpler
Stuck with this for 2 hours now & still confusing

Thankyou

 

[Vogue]

Is paper 1,2,4 physics taken from only the syllabus..do they ever ask anything out of the syllabus....is it the same for experiments in the syllabus...like describe experiment for total internal reflection....do they ask experiments which is not in the syllabus

all the experiments will b related to the topics that r in syllabus

 

[Vogue]

Can anyone plz explain the mechanism of how the van de graaff generator work in , & it would be better if pictures are included to make it simpler
Stuck with this for 2 hours now & still confusing

Thankyou

as far as i no, its not in the syllabus so dunt worry

 

[daredevil]

can anyone plz give me some notes on water purification for chemistry beczuse the mcq.s keep occuring and i don't kow that stuff all i know is chloirne is needed to kill bacteria and fluorine helps in making teeth stronger or sumfin.... otherwise i don't know a thing about it. and htere was an mcq in june 2010 paper *i think* where they asked why CO2 (or CO) i'm still not sure is used in water purification and i didn't know that. plz give me some notes. i cud search the internet but there is unesassry detail there. HELP FELLOW VICTIMS!!! :/

 

[khizer shahab]

can anyone plz give me some notes on water purification for chemistry beczuse the mcq.s keep occuring and i don't kow that stuff all i know is chloirne is needed to kill bacteria and fluorine helps in making teeth stronger or sumfin.... otherwise i don't know a thing about it. and htere was an mcq in june 2010 paper *i think* where they asked why CO2 (or CO) i'm still not sure is used in water purification and i didn't know that. plz give me some notes. i cud search the internet but there is unesassry detail there. HELP FELLOW VICTIMS!!! :/

Water purification is carried out with three simple steps :-
1) Filtration -to remove insoluble particles.
2)Chlorination-to kill bacteria.
3)Carbon treatment- to remove smell.

 

[ashiqbal]

Can anyone plz explain the mechanism of how the van de graaff generator work in , & it would be better if pictures are included to make it simpler
Stuck with this for 2 hours now & still confusing

Thankyou

i dont thinks the specifics are in our syllabus, though u can easily learn any other use of static electricity, eg electrostatic dust precipitator and spray painting

 

[ashiqbal]

can anyone plz give me some notes on water purification for chemistry beczuse the mcq.s keep occuring and i don't kow that stuff all i know is chloirne is needed to kill bacteria and fluorine helps in making teeth stronger or sumfin.... otherwise i don't know a thing about it. and htere was an mcq in june 2010 paper *i think* where they asked why CO2 (or CO) i'm still not sure is used in water purification and i didn't know that. plz give me some notes. i cud search the internet but there is unesassry detail there. HELP FELLOW VICTIMS!!! :/

do you have the book, " Chemistry: a course for O levels", the green one? there is quite a lot of detail there.

but mainly, the water purified as follows:
1. AgNo3(or some chemical like that) added to clump to large impurities which settle in sedimentary tanks
2.water passed by sand bed to filter small impurities.
3. chlorine added to kill bacteria
4.charcoal(carbon) added to remove odour
5. flouride compounds added to make teeth strong like " Pappu and Papa"

 

[daredevil]

do you have the book, " Chemistry: a course for O levels", the green one? there is quite a lot of detail there.

but mainly, the water purified as follows:
1. AgNo3(or some chemical like that) added to clump to large impurities which settle in sedimentary tanks
2.water passed by sand bed to filter small impurities.
3. chlorine added to kill bacteria
4.charcoal(carbon) added to remove odour
5. flouride compounds added to make teeth strong like " Pappu and Papa"

thanku!! that was a huge help... at least it will do for the mcq part ... other than that detail is not needed i think bcuz usually only an mcq comes from here not a paper 2 question so its good... and "Pappu and Papa" !! i won't forget fluorine's function now.... EVER!!

 

[daredevil]

Water purification is carried out with three simple steps :-
1) Filtration -to remove insoluble particles.
2)Chlorination-to kill bacteria.
3)Carbon treatment- to remove smell.

Thanku .... that was helpful!!

 

[khizer shahab]

Thanku .... that was helpful!!

mention not

 

[Spidey21]

so guys i think we should share some difficult questions here as well!!
so anyone has any??

 

[convent2012]

could somebody plz post the experiment of the total internal reflection and how to checked focal length ????

 

[Dukeofwin]

PHYSICS:
Please answer the following question,
Acceleration is also known as or taken as Gravitational Field Strength(or vice versa),
Now if a car moves at constant velocity it Acc is zero,would its G also be zero?
Also a parachute comes down at constant velocity would its G be zero or not?

 

[scouserlfc]

do you have the book, " Chemistry: a course for O levels", the green one? there is quite a lot of detail there.

but mainly, the water purified as follows:
1. AgNo3(or some chemical like that) added to clump to large impurities which settle in sedimentary tanks
2.water passed by sand bed to filter small impurities.
3. chlorine added to kill bacteria
4.charcoal(carbon) added to remove odour
5. flouride compounds added to make teeth strong like " Pappu and Papa"

HEY are u sure its Ag(NO3) and not aluminum sulfate and i got to spank my self for continuously writing sulphate and not sulfur

 

[ashiqbal]

HEY are u sure its Ag(NO3) and not aluminum sulfate and i got to spank my self for continuously writing sulphate and not sulfur

actually, u can just write soluble particles clumped together and settled to bottom of sedimentary tanks, coz i dont actually remember the name of the compound

 

[GetSomeLife]

HEY are u sure its Ag(NO3) and not aluminum sulfate and i got to spank my self for continuously writing sulphate and not sulfur

Aluminium sulphate is added to coagulate small particles of clay so that they form larger clumps, which settle more rapidly
I am sure

 

[ashiqbal]

PHYSICS:
Please answer the following question,
Acceleration is also known as or taken as Gravitational Field Strength(or vice versa),
Now if a car moves at constant velocity it Acc is zero,would its G also be zero?
Also a parachute comes down at constant velocity would its G be zero or not?

to clear your confusion in first part, acc is not the same as gravity. we take acceleration due to force of gravity=10ms-2. and the direction of gravitational force and hence the direction of acc is downward
if a car is moving at constant velocity, its acceleration forward or backward would be zero as there is no resultant force acting on car. however, it is not related to gravity being zero, as there is no resultant force due to gravity(the road pushes the tyre back up), so acceleration downward is also zero, but the gravitational force is continuously acting. and dont confuse acceleration due to gravity with acceleration due to forward force of engine of a car

if a parachute comes down at constant velocity, its acceleration would be zero because the downward force due to gravity is opposed by equal upward force of air resistance. Note that in any case, whether acc is zero or not, there is a gravitational force acting on a body. accceleration is zero only when all forces are balanced(in other words, if there is no resultant force acting on a body)