An electron has been accelerated from rest through a potential difference of 800

Question

An electron has been accelerated from rest through a potential difference of 800 V. You can think of this setup as placing an electron at rest at the negative plate of a parallel plate capacitor. If you release the electron, it will accelerate toward the positive plate. The potential difference is Vpos. plate - Vnet. plate.

a.) . What is the kinetic energy, in electron volts, of the electron as it reaches the positive plate?

b.)  What is its kinetic energy, in joules?

c.) What is its speed?

points has bee ted fro rest through a potential diffe 800 Yo think of this setup plate. The potential di is Vpos. plate Vnet plate fference in lectron volts, of lectron asit hes the positive plat What kineti b. What is its kinetic energy, in joules? ts speed Submit Answer Save Progress ectron at rest at the negati plate of plate pacitor If n, it Notes o Ask Your Teacher My rd the positi

Explanation / Answer

# Solution of part a

Here we would apply conservation of energy. When electron reaches the positive plate, all the Potential Energy (PE) gets converted into the Kinectic Energy (KE).

Hence KE= PE=qV=e800 or

KE= 800 eV. Ans.

# Solution of part b

We know that 1 eV= 1.6 * 10-19 J.

Hence 800 eV = 800*1.6*10-19 J =1280* 10-19 J Ans.

# Solution of part c

From part a we have KE= 800 eV = 1280*10-19 J

so 1/2mv2 = 1280*10-19 where m is mass of electron and v is its velocity

Note m=mass of electron is 9.1 * 10 -31 Kg

so v2 = 2*1280*10-19/m = 2560*10-19/9.1*10-31= 281.31*1012

So v = 16.77*106 m/s Ans

Please note, if we have to find the speed in m/s, we need to put all the values in SI unit i.e. for PE it would be in joule abd for mass m it would be in Kg.

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