Home
Class 12
PHYSICS
The constant A in the Richordson-Dushman...

The constant `A` in the Richordson-Dushman equation is `60 xx 10^4 A m^(-2) K^(-2)` for tungsten. A tungsten cathode has a total surface area of `2.0 xx 10^(-5) m^2` and operates at `2000 K`. The work function of tungsten is `4.55 eV`. Calculate the electric current due to thermionic emission.

Text Solution

Verified by Experts

The Richardson-Dushman equation is
`I = AST^2 e^(-varphi)/(kT)`
We have, `varphi/kT = (4.55 eV)/((8.62 xx 10^(-5) eV K^(-1) (2000 K)`
`=26.4`.
Thus, the thus, the thermionic current `i` is
`=60 xx 10^4 A m^(-2) K^(-2) xx (2.0 xx 10^(-5) xx (2000 K)^2 xx e^(-26.4)`
`= (4.8 xx 10^5 A) e^(-264) = 0.16 mA`.
Promotional Banner

Topper's Solved these Questions

  • ELECTRIC CURRENT THROUGH GASES

    HC VERMA|Exercise Short Answer|10 Videos

  • ELECTRIC CURRENT THROUGH GASES

    HC VERMA|Exercise Objective 1|9 Videos

  • ELECTRIC CURRENT THROUGH GASES

    HC VERMA|Exercise Exercises|23 Videos

  • ELECTRIC CURRENT IN CONDUCTORS

    HC VERMA|Exercise Exercises|84 Videos

  • ELECTRIC FIELD AND POTENTIAL

    HC VERMA|Exercise Exercises|75 Videos

Similar Questions

Explore conceptually related problems

The saturation current from a thoriated-tungsten cathode at 2000 K is 100 mA . What will be the saturation current for a pure-tungsten cathode of the same surface area operating at the same temperature? The constant A in the Richardson-Dushman equation is 60 xx 10^4 A m^(-2) K^(-2) for pure tungsten and 3.0 xx 10^(4) A m^(-2) K^(-2) for thoriated tungsten. The work function of pure tungsten is 4.5 eV and that of thoriated tungsten is 2.6 eV .

The constant A in the Richardson-Dushman equation for tungsten is 60 xx 10^(4) A m^(-2) . The work function of tungsten is 4.5 eV . A tungsten cathode having a surface area 2.0 xx 10^(-5) m^2 is heated by a 24 W electric heater. In steady state, the heat radiated by the cathode equals the energy input by the heater and the temperature becomes constant. Assuming that the cathode radiates like a blackbody, calculate the saturation current due to thermions. Take Stefan constant = 6 xx 10^(-8) W m^(-2) K^(-4) . Assume that the thermions take only a small fraction of the heat supplied.

If the temperature of a tungsten filament is raised from 2000 K to 2010 K , by what factor does the emission current change? Work function of tungsten is 4.5 eV .

A photon of wavelength 4 xx 10^(-7)m strikes on metal surface, The work function of the metal is 2.13eV . The velocity of the photo electron is

Calcuate n(T)//n (1000 K) for tungsten emitter at T = 300 K, 2000 K and 3000 K where n(T) represent the number of thermions emitted per secodn by the surface at temperature. T . Work function of tungsten is 4.52 eV .

Photoelectric work function for a surface is 2.4 eV. Light of wavelength 6.8 xx 10^(-7) m shines on the surface. Find the frequency of incident light and also the threshold frequency. Will there be photoelectric emission or not ?

If K_(h) (hydrolysis constant) for anilinium ion is 2.4xx10^(-5) M , then K_(b) for aniline will be

The electrodes in a conductivity cell have area 1.2 xx 10^(-4) m^(2) and they are fixed 3 xx 10^(-3) m apart. A solution containing 200 g equivalent of the electrolyte per m^(3) of the solution has a resistance of 60 ohm at 298 K. Calculate the equivalnt conductivity of the solution .