Vacuum Tubes
Q.1
Thermionic emission from oxide-coated cathodes takes place at a temperature of about ::
(a) 1000 degree C
(b) 2000 degree C
(c) 100 degree C
Ans:: a
Q.2
Vacuum tubes are used, instead of solid state devices, where ::
(a) very high power is handled
(b) very long lifetime is desirable
(c) very low frequency signal is involved
Ans:: a
Q.3
The control grid of a triode is usually kept at a negative potential so as to ::
(a) make the grid current zero
(b) reduce the effect of space charge
(c) limit the plate current to safe values
Ans:: a
Q.4
The output power of a triode amplifier is greater than the input power. This extra power ::
(a) comes from the input signal source
(b) comes from the d.c. sources
(c) violates the principle of conservation of energy
Ans:: b
Q.5
Temperature limited current in a diode valve is given by ::
(a) Child-Langmuir Law
(b) Richardson's equation
(c) Ohm's Law
Ans:: b
Q.6
Space charge limited current in a diode valve is given by ::
(a) Child-Langmuir Law
(b) Richardson's equation
(c) Ohm's Law
Ans:: a
Q.7
gm of a triode valve can be increased by ::
(a) decreasing the cathode-grid spacing
(b) increasing the cathode-grid spacing
(c) decreasing the cathode size
Ans:: a
Q.8
ยต of a triode valve can be increased by ::
(a) increasing grid wire spacing
(b) increasing grid-plate spacing
(c) increasing the plate current
Ans:: b
Q.9
The shape of the plate of a vacuum diode or triode is ::
(a) rectangular
(b) circular
(c) cylindrical
(d) straight
Ans:: c
Q.10
Schottky effect originates from ::
(a) thermionic emission
(b) photoemission
(c) secondary emission
(d) field emission
Ans:: d
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