How Does the Direction of Fields Affect Charged Particle Motion?

[Jahnavi]

Homework Statement

Homework Equations

The Attempt at a Solution

I am not quite understanding what is given in the question .Are the two directions of the fields known to us ?

Assuming we know the two directions , say for example if we know that the two fields are in x and y directions , but we don't know which one points in x direction .

Now if we fire the charged particle in y direction and path is parabolic , then magnetic field is in y direction and electric field is in x direction .If not , then particle is fired in x direction and path of particle is analysed .

But correct answer is option c) . Could someone help me understand how option C) is correct ? What does it mean to fire the particle in opposite direction ?

 

[gneill]

Have you been introduced to the vector form of the Lorentz Force equation?

 

[PumpkinCougar95]

What happens to the magnetic force when Velocity vector flips direction? Does it flip too?

 

[Jahnavi]

Thank you for replying .

Have you been introduced to the vector form of the Lorentz Force equation?

qv × B + qE

 

[Jahnavi]

What happens to the magnetic force when Velocity vector flips direction? Does it flip too?

Force changes direction .

 

[PumpkinCougar95]

Yes, so if you were to fire the particle from opposite directions, what would happen to the deflection?

 

[Jahnavi]

Yes, so if you were to fire the particle from opposite directions, what would happen to the deflection?

That's exactly what I don't understand . What do you mean by firing the particle in opposite directions .

Direction of what and opposite to what ?

Does the question imply that the two directions of fields are known to us ?

 

[Jahnavi]

@gneill , is their only one field (either magnetic or electric) present in the region ?

 

[gneill]

@gneill , is their only one field (either magnetic or electric) present in the region ?

I would think so, yes. I believe that the idea is to determine whether the field in a region is a magnetic or an electric field.

By "firing in the opposite direction" they mean reversing the particle's initial velocity.

 

[Jahnavi]

I would think so, yes. I believe that the idea is to determine whether the field in a region is a magnetic or an electric field.

By "firing in the opposite direction" they mean reversing the particle's initial velocity.

Oh ! I was interpreting it differently .I was thinking that both the fields are simultaneously present in the region but their directions were known .But which field was pointing in which direction was not known .

On re reading the problem , I think my interpretation is not entirely wrong or is it ?

 

[gneill]

In my mind, if you are asked to distinguish between two things, it will be one or the other but not both.

 

[Jahnavi]

Thanks gneill !

 

[Jahnavi]

@gneill ,

I might be over thinking but why can't option A) be correct ?

If field is directed along x-axis and charge is fired in y direction then the plane in which particle moves can help us distinguish between electric and magnetic field .

If it moves in only x-y plane then field is electric , else magnetic .

Please help me understand why the above reasoning is wrong and option a) is incorrect .

 

[gneill]

Perhaps the question is poorly presented. If you knew in advance the direction of the field then you could determine the nature of the field by the behavior of a charged particle projected perpendicularly to the field, as the plane of the trajectory would be an indicator, as you've surmised.

I think that the intent was for you to recognize that only the magnetic component of the Lorentz Force is affected by the velocity vector.