Numericals (Part - 8) - Moving Charges & Magnetism Video Lecture - Class 12

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going ahead with part 8 let us look at
the next problem if the magnetic field
is parallel to the positive Y axis okay
let us say this is positive Y axis and
magnetic field is parallel to positive Y
axis and the charged particle is moving
along positive x axis so let us suppose
this is a Mac okay another convention
which we follow everywhere is whenever
you have a cross that means that the
magnetic field is acting downwards
downwards means it is perpendicular to
the plane of your screen or the plane of
the paper and it is acting downwards
whenever I denote it with a dot that
means the magnetic field is
perpendicular to the plane of the paper
and it is acting upwards right that is
the convention which we follow
everywhere so here it seems that the
magnetic field is parallel to positive Y
axis parallel in the sense the magnetic
field is either acting downwards or
acting upward because my it has to be
perpendicular to the plane as I told you
before also that magnetic field and
velocity of the particle the cross
product of velocity and magnetic field
means that they are in the they are in a
one plane so when it says that magnetic
field is parallel to Y axis that means
it is parallel to this Y axis and along
Y axis it is down up it is towards
downwards that means it is downwards and
then compared to the plane of the paper
and the charge particle is moving along
the positive x axis so this is how your
charged particle is moving it is moving
along the x axis so which way the
Lorentz force would be for a negative
charge and for a positive charge so now
we will first calculate it for a
negative charge right so let us first
calculate it for a niggah
a charge so what would be what would the
Lawrence force be for a negative charge
we know that Lawrence force will be
given by Q into V cross B so your V
cross B will basically determine the
direction so now let us first consider a
positive charge so for a positive charge
you apply right hand rule so what is
happening here your velocity is in this
direction so this is this is the
direction of your velocity right and
your magnetic field is going down
towards this y axis that means Y axis is
the axis which is going downwards that
is it is going backward right that is
how is your Y axis and imagine it in
three dimensions
so how your velocity move your velocity
will become first it is going take all
your fingers towards right and then from
right it is going downwards so when it
is going downwards where is your thumb
pointing so it is first going towards
right and then it is going downwards so
your thumb is pointing towards the z
axis so that means your force will be
towards positive z axis now when you
consider a negative charged particle now
if you consider negative charged
particle the direction will reverse so
your direction will become negative z
axis because in case of a for a positive
particle moving along positive x axis is
equivalent to a negative particle moving
negatively charged particle moving along
negative x axis so if it is moving along
negative x axis you can try that also
for a negative particle later suppose
the velocity is in this direction so in
this case what would be the direction of
the magnetic force take all the four
fingers towards the direction of
velocity and from there it is going down
so your thumb will point downwards this
time right because you take all your
four fingers towards left and
then directed downwards so your thumb
will point towards down downwards that
is towards negative z-axis right okay so
because in this case how it is you take
all your fingers in this direction and
then your thumb goes down right and in
four case of a negative particle you
take all your fingers the four fingers
comes in this direction and then the
fingers will roll like this so your
fingers will roll like this so your
thumb will be downwards so try to
visualize it like this you take all your
four fingers like this roll the fingers
like this and your compass downwards
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