Question

10. What is the direction of the magnetic force on a positive charge and a negative charge that moves as shown in each case shown? Be clear for each. X X XB B xxx X X X Vout V x x x 11. State/diagram the direction of the magnetic field for the following solenoids. Be clear for each.

Answer 1

10. First figure : magnetic field is perpendicular to the plane of paper and directed outwards(out of the paper) and velocity is downward

So for positive charge, v cross B will give magnetic force in left direction and for negative charge, direction of magnetic force will be opposite to that for positive charge because of an additional negative sign, so force will be towards right.

Second figure : magnetic field is towards right and velocity is upwards. So let's take magnetic field along x axis and velocity along y axis, so cross product of velocity and field will be cross product between y and x axis which gives negative of z axis for positive charge.

For positive charge, force will be perpendicular to the plane of paper and downward, that is into the paper. For negative charge force will be out of the paper.

Third figure : magnetic field is into the paper and velocity is towards right. So direction of force will be perpendicular to both velocity and magnetic field and it is cross product of velocity and field.

For positive charge, force is upwards and for negative charge force is downwards.

Figure four: magnetic field is upwards and velocity is into the paper. So from right hand thumb rule, put your palm in direction of velocity and curl it towards the direction of magnetic field, this will give you direction of magnetic force.

For positive charge, magnetic force is towards right and for negative charge force is towards left.

Figure five: magnetic field is towards left and velocity is perpendicular to the plane of paper and out of the plane.

So for positive charge, force is downwards and for negative charge force is upwards.

11. Figure first: current is clockwise in each loops of solenoid, so magnetic field will be in downward direction ⬇️.

Second figure: current in this case is also clockwise in each loop of solenoid, so magnetic field will be in downward direction ⬇️.

Third figure : current is counter clockwise, so magnetic field is in upward direction, that is ⬆️.