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Coating of strontium oxide on Tungsten c...

Coating of strontium oxide on Tungsten cathode in a valve is good for thermionic emission because

A

Work function decreases

B

Work function increases

C

Conductivity of cathode increases

D

Cathode can be heated to high temperature

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A
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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.

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.

Read the passage given below and answer the question: Industrially widely applied esterification reactions are commonly catalysed using mineral liquid acids, such as sulphuric acid and p-toluenesulphonic acid. The catalytic activity of homogeneous catalysts is high. They suffer, however, from several drawbacks, such as their corrosive nature, the existence of side reactions, and the fact that the catalyst cannot be easily separated from the reaction mixture. The use of solid acid catalysts offers an alternative and has received a lot of attention in the past years. Solid acid catalysts are not corrosive and, coated onto a support, they can be easily reused. Examples of solid acid catalysts used in esterification reactions include ion-exchange resins, zeolites and superacids like sulphated zirconia and niobium acid. Ion-exchange resins are the most common heterogeneous catalysts used and have proven to be effective in liquid phase esterification and etherification reactions. Because of their selective adsorption of reactants and swelling nature, these resins not only catalyse the esterification reaction but also affect the equilibrium conversion. Shortcomings include insufficient thermal resistance, which limits the reaction temperature to 120^(@)C , preventing widespread use in industry. Zeolites, like Y, X, BEA, ZSM-5 and MCM 41 offer an interesting alternative and have proven to be efficient catalysts for esterification reactions. Zeolites have found wide application in oil refining, petrochemistry and in the production of fine chemicals. Their success is based on the possibility to prepare zeolites with strong Brønsted acidity that can be controlled within a certain range, combined with a good resistance to high reaction temperatures. In this study, the activity of various commercial available solid acid catalysts is assessed with respect to the esterification of acetic acid with butanol. The ion-exchange resins Amberlyst 15 and Smopex-101, the acid zeolites H-ZSM-5, H-MOR, H-BETA and H-USY, and the solid superacids sulphated zirconia and niobium acid are selected. Comparative esterification experiments have been carried out using the homogeneous catalysts sulphuric acid, p toluenesulphuric acid and a heteropolyacid (HPA). The weight-based activity of the heterogeneous catalysts tested is maximum for Smopex 101. The following table gives the activity of different catalysts in the esterification reaction between acetic acid and butanol at 75^(@)C . Here: k_(obs) : observed reaction rate constant ( m^(3) mol^(-1)s^(-1) ) kc catalysed reaction rate constant ( m^(3)mol^(-1) g_("cat")^(-1)s^(-1) ) Please note: k c = k obs/ amount (in g) (source: PETERS, T., BENES, N., HOLMEN, A., & KEURENTJES, J. (2006). Comparison of commercial solid acid catalysts for the esterification of acetic acid with butanol. Applied Catalysis A: General, 297(2), 182-188. doi:10.1016/j.apcata.2005.09.00) Unit for observed rate constant for esterification reaction is m³ mol^-1s^-1 , so the reaction is:

First Surface Mirror: Normally we use back surface mirrors. These are considered low precision mirrors because they actually have two reflecting surfaces. The first reflecting surface is the initial surface on the pane of glass where a small percentage of light is reflected off the surface. The second reflecting surface is the aluminium coating where a high percentage of light is reflected off the surface. This dual reflection effect of a low precision mirror causes a loss of contrast and image distortion that is undesirable in high precision applications like rear projection systems, scanners and reflecting telescopes. In these cases good image quality is highly preferred, and this is where a front surface mirror is desired for clarity and single image reflection. First surface mirrors are quite common in professional optics. However, compared with back surface mirrors, they have the important disadvantage of being substantially more sensitive. The front surface may be touched, and a metal coating on the front surface is substantially more sensitive than a bare glass surface. For example, fingerprints can easily cause oxidation of the metal. Also, moisture or aggressive gases may cause oxidation of the mirror coating. The front surface coating:

ERRORLESS -ELECTRONICS-Selv Evaluation Test
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  7. In NPN transistor, if doping in base region is increased then collecto...

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  8. In the following circuit I(1) and I(2) are respectively

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  9. In space charge limited region, the plate current in a diode is 10 mA ...

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  10. A triode has a plate resistance of 10 k Omega and amplification factor...

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  11. Pure sodium (Na) is a good conductor of electricity because the 3s and...

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  15. Is the ionisation energy of an isolated free atom different from the i...

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  16. In the following circuit, a voltmeter V is connected across a lamp L. ...

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  19. In the following circuit the equivalent resistance between A and B is

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  21. In circuit in following figure the value of Y is-

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