e/m apparatus
This demo is typically used to illustrate the effect of magnetic fields over the motion of electric charges. The demo consist in showing the deflection of an electron beam by a magnetic field.The beam of electrons is produced inside an electron tube that shuts an stream of electrons in the horizontal direction. Low pressure gas inside the tube makes the electron beam visible. The tube sits in between two Helmhotlz coils, which produce a magnetic field perpendicular to the direction of the electron beam. Increasing the current on the coils increases the magnetic field, which makes the change in direction of the electron beam more pronounced. The intensity of the magnetic field can be made strong enough to force the beam on a circular path, whose radius can be measured.The current through the coils is supplied by an independent DCpower supply and can be varied and measured. The voltage that accelerates the electrons is provided by a high-voltage low-current DC power supply. This high voltage can also be varied and measured. The electrons are supplied by a heated element in the electron tube. This element is heated using an independent low-voltage AC power supply, which is integrated into the high-voltage DC supply.