Concepts Of Physics MCQ Edition [Volume 2]
- Exam
- Concepts Of Physics MCQ Edition [Volume 2]
- Subject
- Physics
- Chapter
- Electric Current through Gases
Concepts Of Physics MCQ Edition [Volume 2] · Physics · Electric Current through Gases
If the plate current in a diode is found to be zero, it is possible...
If the plate current in a diode is found to be zero, it is possible that
Options
- Athe plate voltage is highly positive and the filament is highly heated
- Bthe temperature of the filament is low
- Cthe plate voltage is zero
- Dthe plate voltage is slightly negative
Correct answer
D. the plate voltage is slightly negative
Step-by-step solution
The plate current in a vacuum diode is zero when no electrons reach the anode (plate). This can occur due to the following reasons:
If the temperature of the filament is low, thermionic emission does not occur, meaning no electrons are emitted from the cathode.
If the plate voltage is zero, there is no accelerating electric field to attract the electrons towards the plate. In an ideal diode, this results in zero plate current.
If the plate voltage is slightly negative, it acts as a retarding potential. This repels the emitted electrons back towards the cathode, preventing them from reaching the plate and making the current zero.
A highly positive plate voltage with a highly heated filament would result in a large plate current, not zero.
If the temperature of the filament is low, thermionic emission does not occur, meaning no electrons are emitted from the cathode.
If the plate voltage is zero, there is no accelerating electric field to attract the electrons towards the plate. In an ideal diode, this results in zero plate current.
If the plate voltage is slightly negative, it acts as a retarding potential. This repels the emitted electrons back towards the cathode, preventing them from reaching the plate and making the current zero.
A highly positive plate voltage with a highly heated filament would result in a large plate current, not zero.