Physics · Magnetism and Electromagnetic Induction

The currently accepted value for e/m is 1.758820 × 1011 C/kg. When an electron enters a region in which there is a uniform magnetic field, B, perpendicular to the velocity, v, of the electron (Caution: The capital letter V will be used below to represent voltage.

This option is incorrect. The correct expression for the e/m (charge-to-mass) ratio of an electron in an electric (E) and magnetic (B) field is e/m = E/(B^2 * r), where e is the charge of the electron, m is its mass, E is the electric field strength, B is the magnetic field strength, and r is the radius of the circular path followed by the electron. 

This option is the correct expression for the e/m ratio of an electron in an electric and magnetic field. As mentioned earlier, e/m = E/(B² * r) is the equation that relates the charge-to-mass ratio of an electron to the electric field strength, magnetic field strength, and the radius of the circular path it follows under the influence of both fields. 

This option is not the correct expression for the e/m ratio. The correct expression is e/m = E/(B² * r), as stated in option (b). 

This option is also not the correct expression for the e/m ratio. The correct expression is e/m = E/(B² * r), as stated in option (b).