State the condition for a charged particle to experience a force in a magnetic field.
State an expression for the magnetic force 
acting on a charged particle in a magnetic field of flux density 
. Explain any other symbols you use.
A sample of a conductor with rectangular faces is situated in a magnetic field, as shown in the figure below.
The magnetic field is normal to face ABCD in the downward direction. Electrons enter face CDHG at right-angles to the face. As the electrons pass through the conductor, they experience a force due to the magnetic field.
On the figure above, shade the face to which the electrons tend to move as a result of this force.
The movement of the electrons in the magnetic field causes a potential difference between two faces of the conductor. Using the lettering from the figure above, state the faces between which this potential difference will occur
is the magnitude of the charge on the charged particle, 
is the velocity of the charged particle and 
is the angle between the direction of the magnetic field and velocity or direction of motion of the charged particle.
