Question

# An electron beam accelerated from rest through a potential difference of 500V in vacuum is allowed to impinge on a surface normally. The incident current is 50μA and if the electrons come to rest on striking the surface the force on it is

A
1.1924×108N
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B
2.1×108N
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C
1.6×108N
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D
1.6×106N
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Solution

## The correct option is A 1.1924×10−8NPotential difference =500Vincident current =50×10−6ATotal current is A=50×10−6Achange of a electron C=1.6×10−19CTotal number of electron per second n=Ae=3.125×1014Total energy KE=eV =1.6×10−19×5000 =8×10−16yforce on wall will be equal to change in momentum of n electron is one second.Let, P= moment and m be the mass of electronSo, KE=P22mP2=2m×KEP=3.8×10−23Total force is F=nP =3.125×1014×3.8×10−23 =1.19×10−8N

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