Question
An electron travelling with a speed $$u$$ along the positive $$x$$-axis enters into a region of magnetic field where $$B = - {B_0}\hat k\left( {x > 0} \right).$$ It comes out of the region with speed $$v$$ then
A.
$$v = u\,{\text{at}}\,y > 0$$
B.
$$v = u\,{\text{at}}\,y < 0$$
C.
$$v > u\,{\text{at}}\,y > 0$$
D.
$$v > u\,{\text{at}}\,y < 0$$
Answer :
$$v = u\,{\text{at}}\,y < 0$$
Solution :
The force acting on electron will be perpendicular to the direction of velocity till the electron remains in the magnetic field. So the electron will follow the path as given.