An ionized gas contains both positive and negative ions . If it is subjected simultaneously to an electric field along the ` +x` - direction and a magnetic field along the ` +y` - direction and the negative ions towardws `-y` - direction

Options

A. positive ions deflect towards`+Y `direction and negative ions towards` -Y` direction.
B. all ions deflect towards `+Y` direction.
C. all ions deflect towards `-Y` direction.
D. positive ions deflect towards` -Y` direction and negative ions towards `+Y` directions.

Answer

c

Explanation

Positive ions will gain velocity due to electric field along positive x-direction. So the direction of force will be `hat i xx hat k = - hat j`. Hence, the positive ions will be deflected towarda negative y direction .
Similarly, negative ions will gain velocity along negative X-axis which is opposite to electric field. Magnetic field is along positive 2-direction hence magnetic force will be along `- ( - hat i xx hat k ) = - hat j` . Hence negative charge will also be deflected towards negative y-direction. Here, the opposite direction of velocity is compensated by the negative charge and direction of magnetic force remains the same. Hence option (c) is correct.