SOLUTION

Peak reverse voltage,V_R:– Peak inverse voltage is the peak voltage that appears across the diode when it is not conducting. In other words, it is the maximum voltage that the diode can withstand under reverse bias conditions.

A PN junction is known as a semiconductor diode or crystal diode.

A PN-junction diode is formed when a p-type semiconductor is fused to an n-type semiconductor creating a potential barrier voltage across the diode junction.

Vacuum-tube diode, the simplest type of vacuum tube consisting of cathode and anode. Since electrons can flow only from the cathode to anode, the vacuum-tube diode serves as the rectifier. A vacuum diode is not a semiconductor diode

The reverse electric field in a diode manifests over atomic distances while in a vacuum tube it manifests itself over centimeters between plates hence in the former a small field is acting over a small distance while in the latter a larger field is necessary due to the inverse relationship of distance to electric field strength.

The Vacuum Diode. The vacuum divide is best suited for use in rectifiers delivering several hundred volts or higher at currents of the order of milliamperes to hundreds of milliamperes. Even small receiving-type tubes have peak inverse voltage ratings in the region of 1500 volts, and tubes with inverse voltage ratings in the range frown 50,000 to 150,000 volts are not uncommon whereas crystal diodes are designed to breakdown at a specific reverse voltage in order to avoid any damage),  PIV rating of a generic “rectifier” diode is at least 50 volts at room temperature.