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Question

A stream of electrons from a heated filament was passed between two charged plates kept at a potential difference Vesu. If e and m are the charge and mass of an electron, respectively, then the value of hλ is given as?


A

2meV

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B

meV

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C

2meV

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D

meV

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Solution

The correct option is C

2meV


Step 1: Given

Potential difference =Vesu

charge of electron = e

mass of electron = m

Plank's constant, h

Step 2: Formula used

Kinetic energy =eV

eV=12mu2u=2eVm-----(1)

Here, u is velocity of electron.

The de broglie wavelength, λ=planck'sconstantmomentum=hmu

hλ=mu-----(2)

Step 3: Calculation

Substituting eq (1) in eq (2)

hλ=m2eVmhλ=2meV

Hence, option (c) is correct.


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