Physics and Chemistry Help

[ds29]

Hey many thanks for any help given.

For Physics I'd like someone to explain to me how op-amps work especially with the whole negative feedback, inverting op-ams and non-inverting op-amps.

For Chemistry I need some help with Biochemistry, especially DNA, RNA, the metals in biochem thing, sodium potassium pump and so on.

Also any idea on what's coming for this time's Practical exams for both of the subjects?

 

[Zohaib Sherazi]

DNA(Deoxyribonucleic acid) is found in chromosomes, inside the cell nucleus. It has specific loci where the gene resides. It carries codes for the making of different proteins in the body. DNA comprises of a deoxyribose sugar, phospho diester bonds, 4 basis adenine, thymine, cytosine, guanine. These show complementary base pairing, joined by hydrogen bonds. RNA (ribonucleic acid) comprises of ribose sugar, 4 bases uracil, guanine, cytosine, adenine. RNA nucleotides are found within the nucleus.

Sodium-Potassuim pump is a protein (intrinsic protein) found in the cell membrane. It can move sodium-potassium ions across cell membranes to change the solute and hence electrochemical gradient inside and outside the cell.

And this is one of the best that you will find for op-amps http://williamson-labs.com/480_opam.htm

 

[princesszahra]

first of all u need to know the propertis of op amp
if u understand this the function will be very clear
properties of ideal operational apmlifiers------
1 infinite input impdence
this means that no current flows
impedence usually refers to resistance that is the obstruction to the flow of current
2 infinite open loop gain
this refers to the fact that there is no fed back
i will explain feed back later on in this post
open loop gain =Ao= V out / V in
if Ao is very high , v out will be very high
3 zero output impedence
this means that nothing is held back ie whole of the output can be recieved
4 infinite bandwith
bandwith means range of freqencies
infinite bandwith means an ideal op amp can work on a range of frequencies
ie all the frequencies are amolified by the same factor
5 infinite slew rate
this means that there is no delay between changes in the input and consequent changes in the out put.

*** real amplifiers deviate from the ideal apmlifiers
this causes the properties to deviate a litttle
1 input inpedence is usually 10^6 to 10 ^ 12

ill have dinner and post the rest!
there's alot more!
hold plz

 

[princesszahra]

the properties of ideal op amps r given in the application booklet
and then u need to know about the working of LED's
u gotta remember the formulas
if i get time ill post my original notes here
there much more in there
mostly from the understanding that teacher taught in class

negitive feeb back is when some of the outout is taken and returned to the input
u see there r two formulas for feed back in the booklet
one for negitive feedback and one for +ve ( u need not say +ve i wrote it so u understand)
feedback is helpful for op amp cuz it increases bandwith , make it more stable and distortion is less.
distortion is smthing like when u talk in mic sometimes the voice the other person hears in like with stops in between
U get it/?
this thing is called distortion

and then u read from the booklet
what all things u dont understand let me know abt em
ill explain em for sure!

 

[Zazzyo]

.. can anyone clearify what is impedence?.. its mentioned everywhere but no defination :l .. even my teacher didnt tell us and i didnt had the courage to ask as i thought its a dumb question and everyone woould know it

 

[badrobot14]

impedence is a fancy wrd 4 resistance actually.

 

[Zazzyo]

lolz.. they even fail when they make physics words 'fancy'

 

[princesszahra]

its not a fancy word
actually impedence means resistances due to capacitor resistor and inductor
u just need to understand that it is the obstruction to the flow of electrons!

 

[Jazib]

I've got a ques on this topic, it may be lame, but still its disturbing me.
when we say, v have Infinite input impedence, this means, no current flows in any input. right?
but if no current flows into inputs, then what is being amplified? :S

 

[princesszahra]

voltage!
it wasnt silly!

 

[Jazib]

V=IR.
I=0
then V=0... now?

 

[princesszahra]

if V=0
then ull get output as the voltage of V supply

 

[Jazib]

hmmm.. that makes sense. thnx!

 

[princesszahra]

ur welcome in the above case the amplifier is said to be saturated!
and this is case of ideal amplifiers but real ampliifers deviate from ideal

 

[Jazib]

aww. saturation reminds me of another.
y do v want to avoid op amp from saturtion?

 

[princesszahra]

saturated op amp is of no use
the difference betwee inverting and non inverting should be very very low
only then u get an output otherwise its voltage is just the supply voltage
if it is saturated u cant use it in any circuit.

 

[Jazib]

umm.this means v can say, saturation "damages" the op amp?

 

[princesszahra]

saturation doesnt allow ap amp to do its job!

 

[Jazib]

oh k... tq again!

 

[princesszahra]

ur welcome any more questions?????????