Write and explain methods to obtain emission of electron from metal.
Write and explain methods to obtain emission of electron from metal.
From metal surface emission of electron can be obtained by following methods.
$(1)$Thermionic emission : When metals are heated (current is passed through filament of metal) electrons are given sufficient heat (thermal) energy, electrons escape from the metal such emission is called thermionic emission.
Example : From diode, triode or TV tube electrons are emitted by using thermionic emission.
$(2) $Field emission : When metal surface are applied electric field of $10^{8} \frac{\mathrm{V}}{\mathrm{m}}$, electron are emitted from it. Such emission is called field emission.
$(3) $Photoelectric emission : When on a clean metal surface incident radiation of proper frequency, electron are emitted from it. Such emission is called photoelectric emission.
Electrons emitted are called photoelectron.
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- [AIIMS 2000]
Answer the following questions:
$(a)$ guarks inside protons and neutrons are thought to carry fractional charges $[(+2 / 3) e ; (-1 / 3) e] .$ Why do they not show up in Millikan's oil-drop experiment?
$(b)$ What is so special about the combination $e / m ?$ Why do we not simply talk of $e$ and $m$ separately?
$(c)$ Why should gases be insulators at ordinary pressures and start conducting at very low pressures?
$(d)$ Every metal has a definite work function. Why do all photoelectrons not come out with the same energy if incident radiation is monochromatic? Why is there an energy distribution of photoelectrons?
$(e)$ The energy and momentum of an electron are related to the frequency and wavelength of the assoctated matter wave by the relations:
$E=h v, p=\frac{h}{\lambda}$
But while the value of $\lambda$ is physically significant, the value of $v$ (and therefore, the value of the phase speed $v \lambda$ ) has no physical significance. Why?
Answer the following questions:
$(a)$ guarks inside protons and neutrons are thought to carry fractional charges $[(+2 / 3) e ; (-1 / 3) e] .$ Why do they not show up in Millikan's oil-drop experiment?
$(b)$ What is so special about the combination $e / m ?$ Why do we not simply talk of $e$ and $m$ separately?
$(c)$ Why should gases be insulators at ordinary pressures and start conducting at very low pressures?
$(d)$ Every metal has a definite work function. Why do all photoelectrons not come out with the same energy if incident radiation is monochromatic? Why is there an energy distribution of photoelectrons?
$(e)$ The energy and momentum of an electron are related to the frequency and wavelength of the assoctated matter wave by the relations:
$E=h v, p=\frac{h}{\lambda}$
But while the value of $\lambda$ is physically significant, the value of $v$ (and therefore, the value of the phase speed $v \lambda$ ) has no physical significance. Why?
The mass of a particle is $400$ times than that of an electron and the charge is double. The particle is accelerated by $5 V$. Initially the particle remained in rest, then its final kinetic energy will be ........... $eV$
The mass of a particle is $400$ times than that of an electron and the charge is double. The particle is accelerated by $5 V$. Initially the particle remained in rest, then its final kinetic energy will be ........... $eV$
In a Millikan's oil drop experiment the charge on an oil drop is calculated to be $6.35 \times {10^{ - 19}}C$. The number of excess electrons on the drop is
In a Millikan's oil drop experiment the charge on an oil drop is calculated to be $6.35 \times {10^{ - 19}}C$. The number of excess electrons on the drop is