Question

State the Principles behind working of HOT CATHODE RAY TUBE.

• A. i) Thermionic emission ii) Electric and Magnetic fields cannot deflect electrons iii) Scintillation
• B. i) Thermionic emission ii) Electric and Magnetic fields can accelerate and deflect electrons iii) Scintillation
• C. i) Thermionic emission ii) Electric and Magnetic fields can accelerate and deflect electrons iii) oxidation
• D. i) Photoelectric effect ii) Electric and Magnetic fields cannot accelerate electrons iii) Scintillation
• E. i) Photoelectric effect ii) Electric and Magnetic fields can accelerate and deflect electrons iii) oxidation

Answer 1

The correct option is B

i) Thermionic emission ii) Electric and Magnetic fields can accelerate and deflect electrons iii) Scintillation

Tungsten is a suitable metal for Thermionic emission, has a high melting point of 3655 K but its work function is high at about 4.52 eV(electron volt-energy unit). It starts emission at 2500 K. If thoriated tungsten (coated with carbon and thorium) is used work function reduces to 2.6 eV and emission begins at 2000 K. If tungsten is coated with barium and strontium oxide work function reduces to 1 eV and emission begins at 1000 K and a good supply of electrons is obtained.