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Topic: static electicity

I've read in the academic books that when a glass rod is rubbed on a piece of cloth and is brought near the water stream falling continuously from a tap, the water stream is deflected towards the rod. This happens because the electric charge is collected on the rod due to rubbing on the cloth. Water is polar in nature. It contains positive  H+ ions and negative OH- ions. As the rod is charged, it attracts one of these ions ( as per the nature of the charge on the rod ) which causes the deflection of the water stream. Is this reasoning correct?

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Re: static electicity

Molecule of a water is of polar nature.  So it bears a charge. But this does not mean that molecule of water is an entirely charged molecule. Polar molecule is the one which has a partial segregation of positive charge on one portion of the molecule and partial segregation of  negative charge on some other portion of the molecule. 

In the case of water molecule, this happens because oxygen has more affinity for electrons than hydrogen. However, overall charge on the molecule continues to be zero. Hence, bringing a rod charged with static electricity will not cause water molecule getting attracted towards the charged rod. You can check this by bringing a rod near a drop of water placed on plastic of any non-conducting material. Drop will not get affected.

But when the charged rod is brought near a thin stream of water coming out of tap, stream gets attracted towards the rod. This may be probably due to static electricity induced in the stream of water. Since the water is flowing, it is likely that friction (internal drag) amongst the moving drops of water is probability inducing static electricity.

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Re: static electicity

but how a good conductor of electricity is getting induced by static charges? .....  I mean, why the induced electricity is not getting grounded prior to apply the force on the flow of water?

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Re: static electicity

If static electricity is produced in the flowing water stream due to friction, the similar thing ( deflection of stream towards charged rod) should happen with other liquids also, for e.g. alcohol, non-polar oil, kerosene etc. Can anyone explain this ?

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Re: static electicity

Regarding the grounding......
Firstly water is not a good conductor of electricity (unless it contains dissolved salts). Secondly static electricity produced through the internal  friction (drag) is continuously generated. So it does not matter even if the charge is lost to the ground.

Regarding the effect on other liquids......
'The generation of electricity in the present case is through the internal drag' is my speculation.  We observe this phenomenon when stream of water comes out from metal tap or from hole in the plastic container. When we bring a charged rod near a stream of water, the straem is attracted towards the rod. But if the experiment is repeated with an isolated drop of water (placed on a non-conductor), it does not get attracted. This suggests that the phenomenon has to do something with the flow of water.  Because this is the only parameter which is changed. From the attraction towards charged rod in the case of stream of water, it can be expected that charge on the water drops constituting the stream is generated through internal friction. (Water drops can generate such electric charges as can be seen in the case of a thunder bolt.)

If this reasoning is correct, then the same effect should be observed with other liquids also but to varied extent. The extent of effect will depend on the nature of the liquid.

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Re: static electicity

I do not think that the tap water is considered to be de-mineralized water. Unless mentioned clearly, we must consider that the water taken for the experiment is normal tap water with normal mineral contamination in it.
Secondly, the permittivity of such water is considered to be infinity. Therefore, according to Coulomb's law, no force could be generated at the molecules of water.
Now it seems that it is true for stationary water molecules.
In case of flowing water, the static charges cannot play any miracle. Hence, the flow of water might be getting deflected because of the induction and could be derived by dB=(Id/sin thita)/r2. Only here, conductor is point charge and water flow is moving against it.
We must apply right hand thumb rule here by replacing two bodies. Current is stationary and the object is moving w.r.t. the observer.

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Re: static electicity

Dear santoshsaraf,

I did not understand high level physics used in your arguements. I am totally confused....

Why don't you come back to the original query and try to explain the phenomenon in simple words? Of course, simple enough for person like me to understand..... 

Otherwise my confusion will continue.....

Last edited by Confucius (17-08-2011 <> 09:44:11 AM)

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Re: static electicity

ya, for me too, it's very difficult to understand.