Vacuum Tubes Objectives Part 01

01 . Vacuum tube has electrodes confined inside an evacuated1. glass envelope only 2. metal envelope only 3. either of 1 and 2 above

02 . In radio transmitter application vacuum tubes are still being used

03 . Vacuum tubes in a radio transmitter are used to generate high power radio waves

04 . Transistor have not replaced vacuum tubes because high power transistors are not available

05 . Vacuum tubes are still used in some electronic device due to their capacity to handle high power

06 . The emission of electrons in a vacuum diode is achieved by heating

07 . At ordinary temperature energy of free electrons in metal as compare with work function is less

08 . The energy can be provided to electrons to cross the surface barrier by1.heating 2. Electric field 3. Light 4. Any of the above

09 . The principle of emission of electrons from a metal surface under the influence of light is known as photo electric emission

10 . With an indirectly heated cathode , the heater voltage is separate from the cathode circuit

11 . Secondary emission of electrons occurs when the metal surface is bombardment with high energy electrons

12 . Thermionic emission electron emission process is widely used in vacuum tubes

13 . Generally metals with low work function have low melting point

14 . Oxide coated Emitted material has the lowest work function

15 . In a vacuum diode provided with directly heated cathode electrons are emitted from the filament itself

16 . The filament of a vacuum tube can be heated by1. Dc voltage 2.low frequency ac voltage 3. rectified 4. Any of the above

17 . The heater filament of a vacuum tube is usually supplied with ac voltage for heating because ac voltage can be easily obtained from mains

18 . The work function for oxide coated emitter material is 1.0eV

19 . The work function in case of thoriated tungsten is 2.63eV

20 . The work function of pure tungsten is 4.5eV