Charged Particles Discovery of Electron Electron beams in Fields Electron Tubes Measurement of the Charge of the Electron

Cathode Rays (Discharge Tubes) Crooke’s Tubes (1870s) Neon for bright red-orange Oxygen and Nitrogen for purple Thomson’s Experiments: Do atoms have parts?

The Electron gun Thermionic emission The work done on each electron The electron-volt

Electron beams in fields Deflection in a uniform electric field Force on each electron Acceleration of each electron Time taken to travel whole plate width Vertical displacement, y Vertical speed, V y Direction of the beam Speed of the beam at any point

Example An electron gun operating at 3000 V is used to shoot electrons into the space between two oppositely charged parallel plates. The plate spacing is 50 mm and its length is 100 mm. Calculate the deflection of the electrons at the point where they emerge from the field when the plate p.d. is 1000 V. + - d

Electron beams in fields Deflection in a uniform magnetic field The force on the electron The acceleration Radius of the electron path The specific charge, e/m The velocity selector × × × × v F=Bev Electron gun r

Example An electron gun operating at 2000 V is used to shoot electrons into a magnetic field strength of 1.9 mT. The initial angle of the beams is at right angles to the field direction. Calculate the specific charge on an electron if the beam forms a circle of diameter 160 mm. Describe the beam path if the initial direction of the beam is changed to 30  to the field direction.

Electron tubes The TV tube

Electron tubes Oscilloscope tube

Measurement of the charge of an electron (1909)

The End