Question

Fill in the blanks :

The ................................ of tungsten is reduced by coating with barium oxide.

• A. Normal function
  
• B. Force function
  
• C. Power function
  
• D. Work function
  

Answer 1

Answer: (D)

Work function

Barium oxide, and other alkali oxides, help in decreasing the work function of the tungsten cathode. The work function of tungsten(uncoated) is $4.5eV$. However, coating the cathode with barium oxide reduces the work function to around $1.5eV$. Thus, the cathode can emit electrons at a relatively low temperature.