Biology; Chemistry; Physics: Post your doubts here!

[Ghazna12]

Instead of grabbing different books just for nothing, why don't you use net for study? Trust me it is very handy and i do the same. You won't even get bored with all the coloured stuff and study will always be fun...:]

 

[VelaneDeBeaute]

need some help with Physics Syllabus contents
(d)Describe a simple form of a.c generator (rotating coil or rotating magnet) and the use of slip rings where needed.

This explains some of it
Basically an A.C.Generator converts mechanical energy (from the rotation) into electrical. Faraday's law states than an emf will be induced if a conductor rotates in a magnetic field, and if this conductor is connected to a circuit then according to Ohm's law a current will be generated.
As you can see in the picure, in that link, the slip rings are such that the ends of the coils are always in contact with the external circuit as the coil rotates and the slip brushes are also part of this, therefore they connect the circuit of the coils to the external circuit. The emf induced will be transferred through this way to the external circuit. Without them, the emf induced can't be transferred outside.
Oh and one important thing - The generator is like the opposite of the motor, in the generator case we rotate the coil ourselves which generates electricity but in the motor we apply a current and this causes a rotation. :wink:

 

[SalmanPakRocks]

Instead of grabbing different books just for nothing, why don't you use net for study? Trust me it is very handy and i do the same. You won't even get bored with all the coloured stuff and study will always be fun...:]

I do the same but didn't get good resources for these!

need some help with Physics Syllabus contents
(d)Describe a simple form of a.c generator (rotating coil or rotating magnet) and the use of slip rings where needed.

This explains some of it
Basically an A.C.Generator converts mechanical energy (from the rotation) into electrical. Faraday's law states than an emf will be induced if a conductor rotates in a magnetic field, and if this conductor is connected to a circuit then according to Ohm's law a current will be generated.
As you can see in the picure, in that link, the slip rings are such that the ends of the coils are always in contact with the external circuit as the coil rotates and the slip brushes are also part of this, therefore they connect the circuit of the coils to the external circuit. The emf induced will be transferred through this way to the external circuit. Without them, the emf induced can't be transferred outside.
Oh and one important thing - The generator is like the opposite of the motor, in the generator case we rotate the coil ourselves which generates electricity but in the motor we apply a current and this causes a rotation. :wink:

Thank u so much

 

[VelaneDeBeaute]

need some help with Physics Syllabus contents
(h)Discuss the environmental and cost implications of underground power transmission compared of overhead lines.

underground power transmission = once it is laid down, and kahin pe koi masla ho jaye, as if the wire needs to be repaired somewhere, u need to dig the whole route and take the whole wire out. Its time consuming, and kaafi investment is needed as in machinery cuz u need to dis the earth for laying down the wires and blah blah.
overhead lines = its easy to hang the wires on but since the wires are exposed to rain and outer environment, there are chances of short circuiting. But it is a less expensive method so most of the third world countries prefer it. Iss se zyada, i dunno! ardon:

 

[SalmanPakRocks]

The generator is like the opposite of the motor, in the generator case we rotate the coil ourselves which generates electricity but in the motor we apply a current and this causes a rotation. :wink:

So in A.C generator we produce Electrical energy but in DC motor be convert electrical energy to Mechanical energy right?
and Can u provide any good diagram of DC motor as well if u can? thank u very much once again!

 

[snowbrood]

my teacher told me that we could take as much positive charges and negative charges from earth lol we know that positive charges dont move they stay where they are , its the negative charges that move right??

 

[SalmanPakRocks]

my teacher told me that we could take as much positive charges and negative charges from earth lol we know that positive charges dont move they stay where they are , its the negative charges that move right??

Yes the absense of Negetive Charge makes the object poisitively charged!

 

[scouserlfc]

Yup Salman in DC motor u convert electrical energy to mechanical .

Well I have a ques related to chemistry. It is name some social, economic and environmental disadvantages of recycling metals rather than using the ores to make them?
thanks I have three disadvantages want more.

 

[Meesam]

well scourcelfc..herzz the answer for your question....!

Advantages:

SOCIALLY:
PROVIDES JOB AND OTHER OPPORTUNITIES

ECONOMICALLY:
CHEAPER TO RECYCLE METAL BECAUSE OF PRESENCE OF NOT TO MANY IMPURITIES IN IT.

ENVIRONMENTALLY:
POLLUTION OVERCOME BY RECYCLING METALS.

hope it helps......

 

[VelaneDeBeaute]

So in A.C generator we produce Electrical energy but in DC motor be convert electrical energy to Mechanical energy right?
and Can u provide any good diagram of DC motor as well if u can?

Yup right
Check this one. This is a cool web i must say :wink: !

Name some social, economic and environmental disadvantages of recycling metals rather than using the ores to make them?
thanks I have three disadvantages want more.

1. Impurities or very similar metals might be mixed. For instance,
Stainless steel mixed with mild steel results in a low scrap price due to the extra chemical analysis that the mill will have to do at melting.
Brass and bronze will have the same problem and well as some aluminum types.
Broken tools (mostly drills) are sometimes left in a piece of scrap metal which can result in a hard spot in the next application.
Brass, copper and aluminum are some examples of metals with a high scrap value. The might be given away for pennies but once they are recycled, they are worth in dollars. So if they are stolen, there will be a huge financial burden on the recycling firm.
2. Some items, such as freon appliances or infant auto seats, could be hazardous or less energy efficient as they continue to be recycled and used.
3. Reusable products need to be more durable than single use products, and hence require more material per item.
4. Sorting and preparing items for reuse takes time, which is inconvenient for consumers and costs money for businesses.
5. Reuse often requires cleaning or transport, which have environmental costs. E.g. dirty water added to rivers etc. Also, the fuel burnt to move vehicles here and there might produce more Carbon that we actually are planning to save.

Hope this helps. :wink:

 

[scouserlfc]

u bet it helped thanks .

 

[SalmanPakRocks]

Ok guys I need some Help in Remembering the Identification of Ions and gases! Any Ideas how do i remember them?

 

[sweetiepie]

hope this helps

 

[sweetiepie]

http://www.sparknotes.com/chemistry/

A helpful website 4 studying chemistry

 

[SalmanPakRocks]

Can someone help me with these (Physics):
(e)Describe the processes by which the energy is converted from one form to another, including reference to
(1) Chemical/fuel energy (a re-grouping of atoms),
(2) Hydroelectric generation (emphasising the mechanical energies involved)
(3) Nuclear energy
(4) Geothermal energy
(5) Wind energy

 

[scouserlfc]

I guess u describe how the energy changes occur in these all processes and how this conversion of energy in that process occurs.

 

[VelaneDeBeaute]

(e)Describe the processes by which the energy is converted from one form to another, including reference to
(2) Hydroelectric generation (emphasising the mechanical energies involved)

I am gonna write in detail - so you get no more confused !
Water at the top of a very high waterfall possesses gravitational potential energy. As the water falls, this energy is converted into kinetic energy, resulting in a flow at a high velocity.
As the falling water collides with the bulk of the water at the bottom of the waterfall, water splashes randomly and chaotically in all directions. Part of the kinetic energy gained by the falling water is now converted into the kinetic energy of random motion. As a result, the internal energy of the water increases, and the water temperature rises at the bottom of the falls.
This kinetic energy turns the generator which further generates electrical energy!

 

[VelaneDeBeaute]

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

Nuclear energy changes can be spread over Fission and fusion.
Fission is practised on earth by far - for fusin the temperature is still unreachable on our planet!
Nuclear fission: reactions in which an atom's nucleus splits into smaller parts, releasing a large amount of energy in the process. Most commonly this is done by "firing" a neutron at the nucleus of an atom. The energy of the neutron "bullet" causes the target element to split into two (or more) elements that are lighter than the parent atom.

During the fission of U235, three neutrons are released in addition to the two daughter atoms. If these released neutrons collide with nearby U235 nuclei, they can stimulate the fission of these atoms and start a self-sustaining nuclear chain reaction. This chain reaction is the basis of nuclear power. As uranium atoms continue to split, a significant amount of energy is released from the reaction. The heat released during this reaction is harvested and used to generate electrical energy.
2. Nuclear fusion: reactions in which two or more elements "fuse" together to form one larger element, releasing energy in the process. A good example is the fusion of two "heavy" isotopes of hydrogen (deuterium: H2 and tritium: H3) into the element helium.

Fusion reactions release tremendous amounts of energy and are commonly referred to as thermonuclear reactions. Although many people think of the sun as a large fireball, the sun (and all stars) are actually enormous fusion reactors. Stars are primarily gigantic balls of hydrogen gas under tremendous pressure due to gravitational forces. Hydrogen molecules are fused into helium and heavier elements inside of stars, releasing energy that we receive as light and heat.

 

[SalmanPakRocks]

Thank u very much!

 

[VelaneDeBeaute]

^ Anytime