Question on deflection of cathode rays in a magnetic field My book states that :


  When only electric field is applied, the electrons deviate from their
  path and hit the cathode ray tube at point A. Similarly when only
  magnetic field is applied , the electron strikes the cathode ray tube
  at point C.
  


I tried to apply the Fleming's Left hand rule used to find the direction of force on a current carrying wire where the direction of current is taken opposite to the direction of flow of electrons. 

The rule states that : 


  Stretch the thumb, forefinger and middle finger of your left hand such
  that they are mutually perpendicular. If the first finger points in
  the direction of magnetic field and the second finger in the direction
  of current, then the thumb will point in the direction of motion or
  the force acting on the conductor.


Applying this rule I found that the electrons should hit the cathode ray tube at A in a magnetic field . But in the book it is given that they strike it at C.

Please explain me where I went wrong . Thank you.
1)  for individual charges Lorentz force F =q[v*B], so curl your right hand from velocity vector of positive charge towards magnetic field so that your thumb points at the force acting on the charge. Here we have considered positive charge 

2)It is better use this mnemonic to find out the direction of force to avoid confusion

Stretch the thumb, forefinger and middle finger of your right hand such that they are mutually perpendicular


fore finger denote direction of electron moving
middle finger denotes the direction of magnetic field (north to south on outside the magnet)
finally force direction can be found out using your the direction where your thumb is pointing 


The book is correct

Tip- If current is mentioned then Use your left hand, to avoid twisting your hand in weird ways! .