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
