Question

In a vacuum tube -

• A. electrons flow in one direction.
• B. electrons are emitted at the cathode.
• C. thermionic emission of electrons takes place.
• D. All of the above

Answer 1

The correct option is D All of the above

In a vacuum tube, electrons are emitted at the cathode by thermionic emission, which goes from cathode to anode (unidirectional).

Hence, option $\left(D\right)$ is the correct answer.