Electrons and Ions in Magnetic Fields

2 An electron is situated between two plates 20 mm apart having a p.d. of
600 V. Calculate the force on the electron and its initial acceleration in the field, showing the force in a diagram. Is the electron weight negligible?

4.8 x10^-15 N , 5.4 x10¹⁵ ms^-2  weight e ~ 9 x 10^-30 N

3 The force on a charge of 4e between two plates 32mm apart is 8 x 10^-14 N. Calculate the p.d. V between the plates.  4000V

4 An electron beam with a velocity of 10⁶ ms^-1 enters a magnetic field B of 4 x 10^-5 T everywhere normal to the beam. Calculate the radius of the path PQ of the beam. Explain why PQ is curved downwards.

0.14m

6 In an electron tube, electrons from the cathode C start from rest and move to the anode A through a p.d. of 150 V. Calculate the velocity of the electrons on reaching the anode. 7.3 x10⁶ ms^-1
If the electron beam passes through a hole in the anode, and enters a magnetic field of 10^-4 T normal to the direction of the beam, calculate the radius of the circular path XY in the field. 0.41m

9 An electron beam is accelerated by a p.d. of 300 V, and then enters normally a magnetic field of 10^-3 T. Calculate the velocity reached by the electrons and the radius of its path in the magnetic field. 10⁷ ms^-1 5.8 x10² m

11 An electron beam X moves with velocity v towards two horizontal plates A, D which are 10mm apart. When the pd between A and D is 160V and the electric field force is opposed by a uniform magnetic field B of 2mT, the electrons pass straight though the plates undeflected. Find v and draw a sketch showing the field directions. 8 x10⁶ ms^-1

If the electron beam travels in a circular path of 23mm in the B field alone estimate the charge mass ratio (e/m_e) of an electron. 1.7 x10¹¹ Ckg^-1