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A beam of fast moving electrons having c...

A beam of fast moving electrons having cross-sectional area A falls normally on a flat surface. The electrons are absorbed by the surface and the average pressure exerted by the electrons on this surface is found to be P. If the electrons are moving with a speed v, then the effective current through any cross-section of the electron beam is:

A

Ape/(mv)

B

`Ape//(mv^(2))`

C

APV/(me)

D

Apm/(ev)

Text Solution

Verified by Experts

The correct Answer is:
A
Let n be the average no. of electrons per unit volume, present in the beam of electrons, then impulse-momentum theorem gives :
(nAv)(mv) = F, P = F/A, where A, v, m, F & P represents cross sectional area, drift velocity, mass of electron, force and pressure respectively.
`rArr n = P//(mv^(2))`
`therefore i = nAve = (APe)/(mv)`
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Knowledge Check

  • In an atom, an electron moves in an orbit of radius r with a speed v , the equivalent current is.

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