The e/m (electron charge: mass) of electrons
The aim of this experiment was to study the movement and trajectory of an electron that moves perpendicular to a magnetic field and measure the charge-to-mass ratio of an electron.
An electron beam was fired through a magnetic and electric field. These two fields are connected to two power supplies and these power supplies are altered. The alteration of these voltages will change the strength of the electric and magnetic fields. Varying the magnetic and electric fields will change the trajectory of the electron. From this it can be shown that the path of an electron is circular in a uniform magnetic field and parabolic in electric fields. With a known anode voltage from the electron gun and by varying the strengths of the electric and magnetic fields the charge-to-mass ratio of an electron can be calculated.
This experiment was first done by J.J Thomson in 1897. The result from this was that he discovered that the atom was not a fundamental unit of matter and that it had charged constituents that could not be separated. Thomson investigated the nature of the cathode rays which then resulted in the conclusion that the cathode rays were negatively charged constituents of the atom; hence the discovery of the electron.
In this experiment a Thomson tube can be used to measure the deflection of electrons in magnetic and electric fields. A Thomson tube is a cathode ray tube which contains an electron gun and a florescent screen. The florescent screen illuminated when the electron gun was turned on and from this the trajectory of the electrons can be measured. By applying a known voltage for both the electric and magnetic fields the charge of the electron can be deduced.
In this experiment the charge-to-mass ratio was calculated to be 2.24 × 〖10〗^5 C〖Kg〗^(-1).
The power supply to the capacitor plate will set up an electric field, the power supply to the Helmholtz coils will set up a magnetic field and the anode voltage was the accelerating voltage across the electron gun.
The procedure of the experiment is as follows:
The anode voltage was set to 4kV and the voltage across the capacitor plate was set to zero, hence the electric field was zero in magnitude.
The current through the Helmholtz coils was set to 0.1, 0.2 and 0.3 Amps. At each current value the path of the electrons were measured in (x,y) co-ordinates. These co-ordinates were then plotted.
The anode voltage was kept at 4kV and the current through the Helmholtz coils was set to zero.
The voltage across the capacitor plates was set to three different voltages (2 kV, 4kV and 6kV) and the path of the electrons was recorded on a set of (x,y) co-ordinates for each voltage. These co-ordinates were then plotted.
The anode voltage was again set to 4kV. By altering the voltage across the capacitor plates and the current through the Helmholtz coils you...