Biology; Chemistry; Physics: Post your doubts here!

[snowbrood]

Also,can anyone help me out in phy? Papers:
5040_w11_qp22 Q7b(ii)
5040_w11_qp21 Q9b(v)
sorry i cudnt upload the papers..

well for Q7b(ii) well u might have got potiential difference as 195volts we have current=65amps as we know charge=current *time. in this case time is 1second so we will multiply it with 65 and get 65 coulombs we know that potiential difference equals workdone divided by charges flowing in the circuit. lets rearrange this equation and we will get workdone equals potiential difference*charges and we will get 195*65=12675 joules

 

[snowbrood]

Also,can anyone help me out in phy? Papers:
5040_w11_qp22 Q7b(ii)
5040_w11_qp21 Q9b(v)
sorry i cudnt upload the papers..

second question is too easy u knowF=MA. at 80s the accelearation is 20 so we will get 20*1.6*10^6=3.2*10^7..

 

[hassankhan]

I would use the following !
Clamp stand,clamp and then suspend the magnet i have to differentiate !
i will then use iron paper clips and put them on the magnet the one which holds the most clips is the strongest !

FOr b part ! repulsion finds a magnet and the bar only attracted is the iron rod and not magnet as u must have read repulsion is the only test of finding whether a substance is a magnet !

Thnks dude

 

[scouserlfc]

Thnks dude

No problem !

 

[Sweetsilly]

Simple Distillation
Simple Distillation – separation of pure liquid from a solution by condensing vaporised liquid
Condensed pure liquid – distillate
Process of Distillation:
Solution is heated, and steam (pure vapour) is produced. The steam is cooled in condenser to form pure liquid. Solute remains in the flask.
Fractional Distillation
Fractional Distillation – separates mixture of miscible (soluble) liquids with widely differing boiling points.
Use of fractionationg column separates them
Process of Fractional Distillation: E.g. ethanol and water
Mixture of ethanol and water is placed in flask and heated. Ethanol with lower boiling point boils and vaporises first and reach fractionating column then cools and condenses into ethanol as it passes through condenser. Temperature will stay constant until all ethanol is distilled. Water will distil the same way after all ethanol is distilled.
Diagram and Distillation Graph
Uses of fractional distillation:
- Separates pure oxygen and pure nitrogen from liquefied air
- Separates substances in petroleum (crude oil) into fractions
- Separates alcohol to produce alcoholic drinks
Reverse Osmosis
Reverse Osmosis – separates a solution (e.g. seawater) by pressurizing the mixture against a membrane which separates the solute and the solvent
Seawater is pumped under great pressure into a closed container onto a membrane forcing water particles but salt particles to pass through. Some salt particles may still pass through.

Chromatography

Separating Mixtures of Coloured Substances
Obtain a dye sample then put a drop of the sample on a pencil line drawn on the filter paper then dip the paper into a solvent with the level below the spot. The dye will dissolve in solvent and travel up the paper at different speed. Hence they are separated.
Identifying Mixturees of Coloured Substances
In the diagram on the right, drop of sample dye is placed on pencil line. The result shows that:
- The sample dye is made of 3 colours.
- 2 comparison dyes are of one of the compositions of the original dye as the spots are of same colour and distance.
- a comparison dye isn’t part of sample.
Separating and Identifying Mixtures of Colourless Substances
To do this a locating agent is to be sprayed on filter paper.
Locating Agent – a substance that reacts with substances (e.g. sugars) on paper to procuce a coloured product.
Rf Values
To identify unknown dye in the diagram at the very top:
Rf value =
Where x = distance moved by the substance and;
y = distance moved by the solvent
Checking the Purity of Substances
- Pure substances have FIXED MELTING AND BOILING POINTS.
 Pure water boils at 100oC and melts at 0oC.
- Impure substances have NO FIXED MELTING AND BOILING POINTS. They melt and boil at a RANGE OF TEMPERATURES
 e.g. starts boil at 70oC, completes boil at 78oC
 Also, it can VARY melting and boiling points of pure substances.
 e.g. pure water boil at 100oC, but with salt is at 102oC

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Thankssssssssssss

 

[Sweetsilly]

biology help needed-have a look at Q2

Thanks alot

 

[nightmaressana]

can someone please tell me what to write if they give you a question in bio of what is a pyramid of biomass of SEVEN marks?

 

[ashfaaq7]

Thankssssssssssss

NO problem that's why god created friends.

 

[mohammed haris]

why NaHSO4 IS BOTH AN ACID AND SALT?

 

[SalmanPakRocks]

why NaHSO4 IS BOTH AN ACID AND SALT?

its an acid cuz it has H+ ions and salt cuz SO4 ^2-

 

[hamzadar2006]

Assalam-o-Allaikum and Hi everyone ,
hope u all are doin great !

Well as the topic says help for chemistry biology and Physics is available here that means that u can ask any mind blowing question or ask any question regarding a particular topic or ask abt any questions from Past paper or any of your text books. 8) :Yahoo!:

I made this topic so that people dont make many posts asking abt bio,physics or chemistry individually but they can post their reply here where it can be answered with ease and the members wont have to go searching for topics to help! !

So what are u waiting for now write ur questions here !
THANKS and Bye or Allah Hafiz ! :wink: :good:

I am struggling to get great marks in MCQ section in chemistry especially. Please give me some tips to prepare for P1.

 

[hassankhan]

Can anyone help me in this question of physics
Explain.in outline,how a low density cloud of hydrogen in space becomes a star?
Plz be quick

 

[Zaheen]

Hello everyone, I need help on Paper 4 ( alternative to practical ) on Physics, If you can give me some tips, or resources i'd be really thankful!

 

[Most_UniQue]

I am struggling to get great marks in MCQ section in chemistry especially. Please give me some tips to prepare for P1.

Keep on practicing . It makes you perfect!

 

[batool]

why are alcohols neutral?? they have OH ions and are soluble so why are they not alkalis

alcohols are weak acids they dissociate partially in water

 

[batool]

bio: what is potassium's role in humans? is it only needed for blood clotting or something else too?

it helps in muscle action as well

 

[batool]

can someone please tell me what to write if they give you a question in bio of what is a pyramid of biomass of SEVEN marks?

u tell what a pyramid of biomass is n then give an example of a pyramid of biomass

 

[batool]

can someone please tell me what to write if they give you a question in bio of what is a pyramid of biomass of SEVEN marks?

expalin how and why at each trophic level the mass of the particular organism increases or decreases .
hope it helps .

 

[snowbrood]

is it true that emf does not depend upon the resisitivity of the conductor... please give answer with reference to v=ir

 

[scouserlfc]

why NaHSO4 IS BOTH AN ACID AND SALT?

ITs called an acidic salt,because its made of a replaceable hydrogen atom still in the salt which when replaced will form the neutral salt at the moment it contains H atom from an acid plus the salt components so its an acid salt !

alcohols are weak acids they dissociate partially in water

when did Alcohol become weak acids werent Carbooxhylic acids weak acids and not the alcohol,the OH functional group here in alcohol is called a hydroxyl grp dont mix it with the hydroxide !But im still wondering how it can still be an acid when the OH in acid and bases makes a base !

can someone please tell me what to write if they give you a question in bio of what is a pyramid of biomass of SEVEN marks?

I personally dont think u can get a 7 mark question with WHAT but if the case is this then explain what is the pyramid of biomass,the mass at each level what it indicates and then u could give and eg. of a written food chain and draw the labelled pyramid that should be enuf for the 7 marks !

is it true that emf does not depend upon the resisitivity of the conductor... please give answer with reference to v=ir

I do think that EMF of the source or battery depends upon the resistance of the circuit as well because according to the definition of emf - emf is the external work expended per unit of charge to produce an electric potential difference across two open-circuited terminals - this tells the resistance of the circuit is also taken in account so by using v=ir
the v for emf = R (the resisitance of the source + the circuit ) * current of the circuit