Biology; Chemistry; Physics: Post your doubts here!

[VelaneDeBeaute]

(e)Describe the processes by which the energy is converted from one form to another, including reference to
(4) Geothermal energy

Geothermal power plants drill into the ground to extract hot steam which is used to turn the turbines. This can be done in 2 different ways, by just drilling into the ground electrical to kineticand letting steam escape into the turbine (dry steam method)potential energy to kinetic which makes turbines turn, or extracting hot water from the ground and lowering the pressure of it to flash it into steam, which is then used to turn the turbine (flash steam method)basically heat to mechanical energy. The steam used to turn the turbine is then condensed back into water, and then either used for different purposes around the power plant, or returned to the Earth, making geothermal energy sustainable.
Summarising it, The energy changes involved in geothermal energy are heat and electrical, as the heat from the hot rocks underground heat the steam which in turn powers the turbine to create electrical energy.

 

[multixamza01]

Chemistry -

Need help in naming of esters and simple branched hydrocarbons. I can't seem to get hold of the techniques! Koi Allah ka banda hai jo meri mushkil dooor karey?

 

[memyself15]

Chemistry -

Need help in naming of esters and simple branched hydrocarbons. I can't seem to get hold of the techniques! Koi Allah ka banda hai jo meri mushkil dooor karey?

follow these steps:
1. select the longest, continuous chain of carbon atoms in the molecule.if there are 2 or more chains of equal lenght, then select the one with the higher number of branches/subtituents.
2. number the carbon atoms of the chain from the end that gives lower positions to the branches and subtituents.
3. name the branches/subtituents in alphabetical order and indicate their positions.
4. finally, name the longest chain as an alkane having the same number of carbon atoms.

 

[VelaneDeBeaute]

(e)Describe the processes by which the energy is converted from one form to another, including reference to
(5) Wind energy

Basically, the kinetic energy of the wind is used to turn the blades and generate electricity. SO energy change are quite simple here wind => kinetic => electrical!

 

[scouserlfc]

Need some regarding Bio atp, are there any fixed topics which come or everything can come in it.
Thanks

 

[multixamza01]

^^ Anything can come.
But i've noticed that Reproduction In Humans is a frequent question as it is not favoured in MCQs and Theory due to obvious reasons. Apart from that all the tests (Buiret, Benedict ,Starch e.t.c) can come. And then the basic concepts of other chapters can be molded to make a question.

 

[multixamza01]

Physics-

Half life? Someone explain this.

 

[Gémeaux]

itx the time taken for half of the unstable nuclei to decay. fer example if sum elemnt's half lyf is a thousand years, starting with initial count rate of 2000 (initial activity), every 1000 year it'd halve, lyk after frst half lyf it'd b left wid 1000, after another 500, then 250 n so on. n as itx divided by 2 each tym, it wud never b zero..(useful fer graphs cuz the graph wont ever touch the axis)

 

[SalmanPakRocks]

itx the time taken for half of the unstable nuclei to decay. fer example if sum elemnt's half lyf is a thousand years, starting with initial count rate of 2000 (initial activity), every 1000 year it'd halve, lyk after frst half lyf it'd b left wid 1000, after another 500, then 250 n so on. n as itx divided by 2 each tym, it wud never b zero..(useful fer graphs cuz the graph wont ever touch the axis)

Is this in O levels ??

 

[Gémeaux]

itx the time taken for half of the unstable nuclei to decay. fer example if sum elemnt's half lyf is a thousand years, starting with initial count rate of 2000 (initial activity), every 1000 year it'd halve, lyk after frst half lyf it'd b left wid 1000, after another 500, then 250 n so on. n as itx divided by 2 each tym, it wud never b zero..(useful fer graphs cuz the graph wont ever touch the axis)

Is this in O levels ??

yes it is.

 

[Silent Hunter]

yes it is...........its MCQ came in my paper in may 2011

 

[SalmanPakRocks]

Oh! ok! Actually i haven't studied Nuclear physics so didn't have any idea about it!

 

[Anon]

Anyone here who can explain, alkaline and acidic fuel cells ?

 

[multixamza01]

I dont think that's in the syllabus. We only have The Galvanic (Hydrogen-Oxygen) Fuel Cell in our syllabus. Don't we?

 

[falcon678]

I dont think that's in the syllabus. We only have The Galvanic (Hydrogen-Oxygen) Fuel Cell in our syllabus. Don't we?

yes.....its the only one......so no worries bout other cells......i dont even had idea that those cells exists..... :%)

 

[ailg1996]

What is the half life formula??? of radioactive substances?

 

[abcde]

What is the half life formula??? of radioactive substances?

I recall: N = No (1/2)^t , where
No is the initial number of undecayed nuclei
N is the final number of undecayed nuclei
and t is the half life.
Please verify it from someone.

 

[Translucent231]

We have a 100% efficient transformer, following are the details:

Primary coil turns: 1600
secondary coil: 80
Primary voltage : 240V
Secondary voltage: ??
Power of primary coil is 40W

Lamp connected to secondary coil, with a 2.5ohm wire.
Find the current in secondary coil:
Find the voltage across the wire.
power dissipation of the lamp.


i solved it this way: Ip = primary current Is = secondary current
Ns/Np=Vs/Vp
80/1600=Vs/240
1/20=Vs/240
1/20 * 240 = Vs
Vs = 12V --> secondary voltage.
Current in secondary coil : since its a 100% efficient transformer, input power = output power , Vp*Ip=Vs*Is
P=V*Ip for primary
40 = 240*Ip
Ip=40/240
Ip=0.166Amp Ip = primary current

Vs/Vp= Ip/Is
12/240 = 0.166/Is
1/20 = 0.166/Is
Is = 0.166 * 20
Is = 3.32amp ====> Secondary Current

Voltage in wire:

V=IR
V=3.32*2.5
V= 8.3 V

Since wire is obviously in series with the lamp.
The Voltage going into the lamp is 12/8.3= 3.7V
The power dissipation by the lamp:
P =VI
P = 3.7 * 3.32
P= 12.284W



Have I solved the above question correctly? as today in class i pretty much got owned by my physics teacher for being the only retard to solve the question this way, while everyone else got the following answers, :
Is=4amp
Voltage across wire = 10V
Voltage in lamp = 2V
Power dissipation by lamp =8W


i strongly believe i am correct

 

[SalmanPakRocks]

Ur 100% correct but u did a lengthy working!

 

[Translucent231]

didn't want you guys to be in any ambiguity , JUST WANTED IT TO BE CLEAR