1I am waiting for your answer.What's the answer given in the book?
True or false:
An electric line of force( i.e electric field) in the x-y plane is given by the equation x2 +y 2 =1 . A particle with unit positive charge, initially at rest at (1,0) in the xyplane, will move along the line of force.
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28 Answers
23electric field can be circular, for instance the induced electric field
there is nothing but you just need to know the basic thing that force acting on a particle will be tangential to the field lines
1@account blocked
The answer and reason for that question are:
No.It moves along the line of force only if it is straight.
It means that the particle will not move in our case.But why did the book say earlier that the partilce will move?
Please tell me the reason why the particle moves only if the field lines are straight?
And also, it is written in the texbooks that the particle moves along the lines of force.The lines of electric field is the path of the particle described in an electric feild .Isn't it the definition of the electric field?It means that iif the electric field lines are circular then the particle has to move along circular path.
Please if you have read any other definition of electric field lines then tell me.Or if you have any other thing which may explain this thing.I know that the electric field cannot be circular.But even then let us suppose that it exists.
23tnx asish for confiming the ans !!
yeah they just wanted to ask about the particle's path, irrespective of it is covering it in 1 sec or 1 billion years !!! [3]
"the direction of motion does not have to be along the direction of acceleration" - completely agree !!
vinay why are you trusting the book blindly ...
ok do one thing vinay , check out a subjective question of electrostatics of 1979 in that same book , the question is "a charged particle is free to move in an electric field, will it always move along the electric field " ? just tell me whats the ans and whats the reason given ....
1Due to 1c charge 1 line of force will be having some value.For 2c charge 1 line of force willl be having some different magnitude.So we should consider that the line of force is such that it can make the particle move.
1Can't you even feel that the particle will move?Can't you accept the answer that is given in the book.Cantcantcantcant
106@qwerty : in general charges do NOT go along field lines as correctly pointed out by Tush.
the direction of motion does not have to be along the direction of acceleration and im sure u can understand that ..
now coming to this question : this question is incomplete.
reason :
the question states that there is a line of force . this is hypothetical to a very great extreme . If there exists only one line of force, then it wont move at all unless the charge happens to have 0 mass. in that case acceleration can be infinite and it will move. and the motion will be purely along the path x=1..
the main point (which i think they wanted to ask is :)
the direction of motion does not have to be along the direction of acceleration
and hence for any general electric field the statement will be false
1My Dear Account Blocked
I am very really sorry for saying that it is your problem.I am having past year iitjee problems.I saw it in this book.You can also buy this book.I am giving you the name,Tanushree by A.Sinha,Kusum Sharma and J.P. Singht.It contains past year solved 32 years problems.Solutions are in quite detail.
Now let us move onto the question.
As I told you that I am having solution for this problem from an expert,so I am pasting whatever is written in the book about the problem.Please read it:
A line of force represents the path in an electric field along which a unit positive charge moves.
The unit positive charge at A is already on the circular line of force.It will move along the circular line of force.
I have posted whatever was written in the book.If you do not believe it then please buy the book and see it.This question came in IITJEE1988.
Thank you very much!
23ajoy i agree that it is a hypothetical model , but the concepts that we learn dont restrict us to use them for such lines of force, btw if you still dont agree , then you will have to convince the iits as thi is an old iit jee question ..
and i dont know the ans , but i feel it has to be false , one obvious reason is ,
the force that will act on the particle will only be tangential , there isnt any force here to change the direction of the velocity . For circular motion , we need the centripetal force to continuously change the direction of velocity such that the particle's radius of curvature is constant , and hence giving rise to circular motion , but i dont see any such force here [2]
1Dear Ajoy
You might have seen in the books about the diagrams of electric field lines.There are several lines due to a charge.Many lines of force means strong field.Less lines of force means less field.One line of force means that the force can be neglected.But books cannot make such a mistake.So I suggest that this problem has been proposed by account blocked himself.If not,then why did he not give the answer to the problem?
I ask account blocked the third time what is the answer to the problem that is given in the book?
1Electric field is defined as a region in space ,which influnces the force on a particle.How can an electric field be a single line.It is practically and theoritically impossible....Doesnt make much sense to me......
1Dear Sachin
Does conservative mean that the particle will not move?I think you have not read about circular loops carrying current.Don't the particles move in the circular loops?Is there not electric field?
1hey but how can the electric field be lie as a circle as it is conservative...
does it is about the induced E .F. if so on wat basis its produced here........
1True.Because the charge will feel an electric force due to the field which will move the particle.As the direction of field is changing the direction of motion of the particle has also to change.The direction of motion of the particle is same as the direction of field,so the particle will move along the circle.
1The charged particle moves along the line of electric force.So it will move in a circular path.
23tush i also think that the ans is false , bcz the force acting on the particle will give it only tangential velocity at any moment and so the particle will fly off tangentially
1Dear Tush
You should revise your concepts.He writes that the particle was initially at rest.Suppose you are standing and somebody pushes you from behind in the forward direction.Where will you go?You will go in the forward direction.So the charged particle should move in the direction of lines of force.
And also one more big proof.
What are lines of electric force?I think you might have seen the book in which the definition of electric field lines is as follows:
The path traversed by the particle in presence of electric field.So the path of the particle should be the same as that of electric field lines.In this case the electric field lines are circular and so the direction of motion of the charge particle should also be circular.
Hence proved.
11Acc to me, it won't bcoz the direction of motion will be different frm that of acc.
1Ok.But tell me about that experiment.Did you have any centripetal force?And see,I am saying that circular motion always does not mean that there should be a centripetal force.Yuo can see the pen's case.You are just moving it round and round.There is not string tied anywhere.Please if you think I am wrong even then rotate it.There is no centripetal force.So circular motion always does not mean that there should be a centripetal force.
23its not the particle's motion that gives rise to the centripetal force, but its the centripetal force that gives rise to the circular motion ..
1You are right.But the particle has to move along the direction of Electric field lines.As a body has to move in the direction of force,so here it will also move.See what is the centripetal force?It is the force when the particle is moving in a circle towards the centre.We have to consider some force acting on it towards the centre.
23can you please come up with some convincing proof ? many textbooks nowadays make some mistakes, including hcv, after all, we all are humans.. [3]
1And also yes.You are a good questioner.Who will provide the centripetal force?I advise you to perform the following simple experiment
Take your pen and move it in a circle.It will move in the circle.I think you have understood.
1See,I have said that it is due to the line of force.The line of force is such that it forms a circle.And in textbooks it is written that the particle will move along the lines of force.So that's why I am saying this.
23even without a centripetal force? are you sure ??
i can convince you that it wont move on a circle ...btw looking for more views on this ..