106Ashish : dont worry about the third question now , beyond JEE syllabus and it involves relativity
1. A particle moves in a region having uniform magnetic field and a parallel, uniform electric field. At some instant, the velocity of the particle is perpendicular to the field direction. The path of the particle will be
a) a straight line
b) a circle
c) a helix with uniform pitch
d) a helix with non-uniform pitch
2. If a charged particle goes unaccelerated in a region containing electric and magnetic fields,
a) \vec{E} must be perpendicular to \vec{B} .
b) \vec{v} must be perpendicular to \vec{E} .
c) \vec{v} must be perpendicular to \vec{B} .
d) E must be equal to vB.
3. Let \vec{E} and \vec{B} denote electric and magnetic fields in a frame S and \vec{E}' and \vec{B}' in another frame S' moving with respect to S at a velocity \vec{v}. Two of the following equations are wrong. Identify them.
a) B_{y}' =B_{y}+\frac{vE_{z}}{c^{2}}
b) E_{y}' =E_{y}-\frac{vB_{z}}{c^{2}}
c) B_{y}' =B_{y}+vE_{z}
d) E_{y}' =E_{y}+vB_{z}
Note: Please just don't post the answers. Answers are available. These questions are doubts so please provide some explanation. [1]
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10 Answers
3hey! studying after all exams are over?? u must be in 11th then?
the first one......is it a helix with non uniform pitch i think...
since it is perpendicular to the magnetic field and has a finite velocity, it will tend to move in a circular path with its axis parallel to the mag. field.....
and the electric field will go on increasing its velocity along its direction causing a non uniform pitch....
[did not put much thought to it ...so may be wrong....]
the third one is to do with joules-bernoullis eq.....
the answers shud be 'b' and 'c'......its beyond the scope of 11th std i think...:D
anyway good luck with ur prep.
30Thanks a lot bhaiya. The first one is correct.
But, I have no idea how to do the third one. Your answers are correct.
I'm in 12th. Can you tell me how you got to the answer to the third question?
1063but ashish........all ur exams shud be ovr by now rite??
and asish: hi!! how are you??
1yes,it seems to be lorentz transformation...
jee sticks with galileon transformation ..
30All my exams? Nope. There are still many left! :)
Whats lorentz transformation and galileon transformation?
30@Asish bhaiya : Encountered that question in HCV that is why I posted here. Thanks a lot anyway! [1]
1http://en.wikipedia.org/wiki/Lorentz_transformation
http://en.wikipedia.org/wiki/Galilean_transformation
galilean physics is what classical physics is ,i.e the thing which we are studying in 11th and 12th
30Okay. Question 3 was way simpler than I thought. Its an application of Dimensional Analysis, giving (b) and (c) as wrong.
I was wondering why I was the first one here to come up with this doubt if this way out of JEE syllabus. Now I know why! [3]