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Magnetism

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22 Dec 2007 18:35:05 IST

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speed of a chrged particle.....

None

Q. A free point charge q and mass m is at rest as shown in the figure. A constant electric field E=E_oi + 2E_oj and a constant magnetic field B=B_ok is present in the region. The speed of the particle when it reaches the point (3,2,1) , is :
a) 8q.Eo/m b) 14q.Eo/m c) ( 14q.Eo/m)x (E_o/B_o). d) none of these.

Please solve this question.Rates and Salute guaranteed..
Nitish..

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Comments (7)

aditi garg

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22 Dec 2007 19:08:29 IST

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is the answer b)........ill post the solution if the answer is correct

abhishek sinha

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22 Dec 2007 19:58:23 IST

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See the particle can't leave the the xy plane

so it can't reach z= 1

electric forces are in xy plane , magnetic force also ( being a cross product with B ) is in the same plane . Take note of this .

again all the options given dimensionally don't match with that of velocity .

Niteesh Mehra

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22 Dec 2007 20:47:25 IST

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nice logic..The answer is d.....Btw if we wanna solve it then how wud we solve it ?? @ aditi_g
Cud u plz post ur solution ? I'll gve u rates for ur work 4 sure..

aditi garg

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22 Dec 2007 22:55:06 IST

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hey actually i was abt to post the solution too but thn after posting that answer i was wondering how it reached 1 along y axis...all forces and all are in xy plane... the force due to magnetic field will also be in xy plane acc to F = q vX B........
but thn its given in the question to give its velocity at point 321 tahts y i didnt post the solution

abhishek sinha

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23 Dec 2007 20:17:53 IST

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Soln to this type of Qn can be given after writing eqns for each of the vector components seperately and the solving the simultaneous diff eqn .

F = q ( E + v * B )

write F = m d2 / dt2 ( r )

where r = x i + yj + z k and seperate each i, j, k comp.

aditi garg

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23 Dec 2007 20:22:34 IST

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see whn ur just reqd to find the speed and not the velocity take the electric field u know that accelaration = Eq/m
now apply taht v^2 = u^2 + 2as
u can find usng this....
just remeber magnetic field only changes the direction it cannot change the magnitude ie speed reamins same in case of magnetic field...
so just work with electric field to find speed

Niteesh Mehra

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Joined: 28 Oct 2007

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24 Dec 2007 08:28:11 IST

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thanx a lot both of u..

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