A hollow metal sphere A of radius 6 cm is uniformly charged with 10 μC. Another hollow metal sphere B of radius 3 cm is uniformly charged with 6 μC. A and B are connected externally by a wire. What happens now? Will the charge flow?
Ans.
Charge flows from A to B.
Explanation.
A hollow metal sphere with uniform charge acts as if the entire charge were concentrated at its centre; and since the electric field inside is zero, the potential is the same from surface to its centre.
==> V = k*q/r (V-potential, q-charge, r-radius)
VA = k*10/6 & VB = k*6/3 ==> VA < VB
Now, when the two spheres are connected by a wire, charges flow until their potentials become equal; charges that flow through the wire are the free electrons and they will travel from lower to higher potential i.e., from sphere A to B.
Note: However, conventional current flows from B to A.
Electrons flow from lower potential to higher potential and so conventional current flows from higher potential to lower potential.
ReplyDeleteSo question should be asked like,What is the direction of flow of electrons or conventional current immediately when the spheres are connected by a wire
So this question is not correct
You're dead right. Qn. is worded ambiguously. There is no clarity.
DeleteEarlier comment was by kingsley596@gmail.com
ReplyDeleteEarlier comment was by kingsley596@gmail.com
ReplyDeleteElectrons flow from lower potential to higher potential and so conventional current flows from higher potential to lower potential.
ReplyDeleteSo question should be asked like,What is the direction of flow of electrons or conventional current immediately when the spheres are connected by a wire
So this question is not correct
Happy to see such a good argument Sir.
ReplyDeleteYour argument and answer are both Very very correct.
I am happy and Hope You might be Refering / Reading books like Physics by Hallyday - Resnik - Walker,University Physics by Freedman......
Only electron can flow. no positive charge (proton) flow. Hence actually no charge can flow from higher potl to lower potl. So you are right that electrons flow from lower potential to higher. ( Here from A to B).
As you both said the option "current" flow from.... can not be given in a question taken in Unit one electrostatics.
As majority of teachers are now a days confined to State board Text books alone and even slow learners materials!.. You may find it difficult to get acceptance from teachers.
More over, the answer depends on the context and the intention of the question setter and the standard of pupil to whom it is set.
We are trained to say " current flow from higher potential to lower potential".
When we accept current (conventional) flow from higher ptl to lower ptl we are in a position to accept (blindly)charge (conventional) flows from higher potential to lower potential as we follow stateboard text and that to for +2 Students with whom teachers are expected to produce centu result. All the Best. M Palanichamy. Physics PG (Presently HM)
This comment has been removed by the author.
DeleteThanks so much for the detailed, accurate and considerate reply Palanichamy sir. Hope we will keep in touch for some more exciting discussions.
DeleteI read/refer Resnick&Halliday to some extent but more than that I'm a fan of Textbook of Elementary Physics ed by G.S. Landsberg, Questions and Problems in School Physics (Tarasov and Tarasova -- a little gem!) and other such classic Russian books.
Thanks to both the teachers Mr.palanichami sir and Mr.Ravishankar sir, earlier I also had a openien that charge flow from B to A based on surface charge density and I argued with ravishankar sir too then I understood, when we connect externally the entire system can be consider as battery arrangement so charge will flow only from A to B.
ReplyDeleteNow..divine same question is repeated inv the public exam willingly give mere attempt or what is the actual answer sir?
ReplyDelete