An electron moving with a uniform velocity along the positive x-direction enters a magnetic field directed along the positive y-direction. The force on the electron is directed along
The force on the positive charge moving in the magnetic field is given by Fleming's left hand rule which states that if we stretch the thumb, the centre finger and the middle finger of our left hand such that they are mutually perpendicular to each other, the centre finger gives the direction of current and middle finger points in the direction of magnetic field, then the thumb points towards the direction of the force or motion of the conductor. Direction of the moving electron is opposite to the direction of the thumb. Here, the electron is moving in the positive direction and the magnetic field is directed in the positive y-direction, so the force on the electron will be directed in negative z-direction.