Question

4) An electron moving along the +x-axis enters a magnetic field. If the electron experiences a magnetic deflection in the -y direction, then the magnetic field must have a component
(A) along the +z-axis.

(B) along the -z-axis.

(C) along the -x-axis.

(D) along the +y-axis.

(E) along the -y-axis.

Answer 1

Answer:

option (b)

Explanation:

direction of velocity is along + X axis

direction of force is along - Y axis

So, by use of the

$\overrightarrow{F}=q\left ( \overrightarrow{v} \times \overrightarrow{B}\right )$

Where, B be the magnetic field

As charge of electron is negative

so the direction of magnetic field is along negative z axis .

Answer 2

Answer:

B) along the -z-axis.

Explanation:

• According to the Fleming's left hand rule we know that when a positive charge moves with velocity v perpendicular to the direction of magnetic field the it experiences a magnetic force perpendicular to the the plane in which the velocity vector and the magnetic field vector lies.

• As a result all the three vector are mutually perpendicular in such a case.

• Here as per given condition we have a negative charge moving along x-axis which experiences the deflection in -y direction so the magnetic field will be along the negative z axis i.e. into the screen.