MCQs on Valve Electronics (Diode and Triode) for NEET 2020

A diode is a semiconductor device with two terminals. It conducts current only in one direction and restricts the flow in the opposite direction. It is mainly used as a switch.

The triode is a three-terminal device made using metallic filaments. It is used as amplifiers for both audio and radio signals.

Q1: Number of secondary electrons emitted per number of primary electrons depends on

  1. Material of target
  2. Frequency of primary electrons
  3. Intensity
  4. None of the above

Answer: (c) Intensity

Q2: In a diode, when there is saturation current, the plate resistance is

  1. Zero
  2. Infinite
  3. Some finite quantity
  4. Data is insufficient

Answer: (b) Infinite

Q3: The grid voltage of any triode valve is changed from 1 volt to 3 volt and the mutual conductance is 3 x 10-4 mho. The change in plate circuit current will be

  1. 0.8 mA
  2. 0.6 mA
  3. 0.4 mA
  4. 1 mA

Answer: (b) 0.6 mA

Q4: For a given plate voltage the plate current in a triode is maximum when the potential of

  1. The grid is positive and the plate is negative
  2. The grid is positive and the plate is positive
  3. The grid is zero and the plate is positive
  4. The grid is negative and the plate is positive

Answer: (b) The grid is positive and the plate is positive

Q5: The amplification factor of a triode is 20. If the grid potential is reduced by 0.2 volt then to keep the plate current constant its plate voltage is to be increased by

  1. 10 volt
  2. 4 volt
  3. 40 volt
  4. 100 volt

Answer: (b) 4 volt

Q6: The amplification produced by a triode is due to the action of

  1. Filament
  2. Cathode
  3. Grid
  4. plate

Answer: (c) Grid

Q7: In a triode amplifier, the value of maximum gain is equal to

  1. Half the amplification factor
  2. Amplification factor
  3. Twice the amplification factor
  4. Infinity

Answer: (b) Amplification factor

Q8: The voltage gain by the triode depends on

  1. Filament voltage
  2. Plate voltage
  3. Plate resistance
  4. Plate current

Answer: (c) Plate resistance

Q9: In a triode valve

  1. If the grid voltage is zero then plate current will be zero
  2. If the temperature of the filament is doubled, then the thermionic current will also be doubled.
  3. If the temperature of the filament is doubled, then the thermionic current will nearly be four times
  4. At a definite grid voltage, the plate current varies with plate voltage according to Ohm’s law

Answer: (c) If the temperature of the filament is doubled, then the thermionic current will nearly be four times

Q10: In the circuit of a triode valve, there is no change in the plate current, when the plate potential is increased from 200 volt to 220 volt and the grid potential is decreased from 0.5 volt to 1.3 volt. The amplification factor of the valve is

  1. 15
  2. 20
  3. 25
  4. 35

Answer: (c) 25

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