Which scientist invented cathode rays?

Positive rays were discovered by

Assertion: In a photoemissive cell,an inert gas is used.
Reason: An inert gas in the photoemissive cell provides a greater current.

In a Thomson set-up for the determination of $e/m$,electrons accelerated by $2.5 \ kV$ enter the region of crossed electric and magnetic fields of strengths $3.6 \times 10^4 \ Vm^{-1}$ and $1.2 \times 10^{-3} \ T$ respectively and go through undeflected. The measured value of $e/m$ of the electron is equal to

What is the speed of cathode rays?

Explain the emission of electrons from a metal. Define work function. Write its unit,and state the factors upon which the work function of a metal depends.