# deceleration of an electron in an electric field

Two charged, parallel, flat conducting surfaces are spaced d = 1.4 cm apart and produce a potential difference of 655 V between them. An electron is projected from one surface directly toward the second. What is the initial speed of the electron if its comes to rest just at the second surface?

This is what I've been trying to do:

qV=-W=-K=-1/2mv^2

655*-1.6*10^-19=-1/2(9.1*10^-31)v^2

I tried to get everything on one side and just square it to find the initial speed. But I got an incorrect answer.

Why does this not work?

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#### Solution Preview

The equations you used look ok. Let's try again:

The potential energy should decrease by e*655 V = ...

#### Solution Summary

A deceleration of an electron in an electric field is examined. The second surface electron speed is determined.

Four problems on electric field, charge, flux, charge density

1. A conducting rod of radius R1 = 1.57mm and length l=13.9m inside a thin-walled coaxial conducting cylindrical shell of radius R2=13.0R1 and the (same) length l. The net charge on the rod is Q1= +3.43 x 10^-12C; that on the shell is Q2= -2.32Q1. a) What is the magnitude and direction [radially inward or outward] of the electric field at radial distance r=2.00R2? b) What is the magnitude and direction at r=5.01R1? c) What is the charge on the interior and exterior surface of the shell? Give electric fields in N/C and charges in Coulombs.

2. A point particle with charge q=80uC is placed at a corner of a cube of edge a=8.1cm. What is the flux through each cube face forming the corner? and each of the other cube faces?

3. A small, nonconducting ball of mass m=1.3mg and charge q=2.6 x 10-8C (distributed uniformly through its volume) hangs from an insulating thread that makes an angle theta=39 degrees with a vertical, uniformly charged nonconducting sheet. Considering the gravitational force on the ball and assuming the sheet extends far vertically and into and out of the page, calculate the surface charge density of the sheet.

4. An electron enters a region of uniform electric field with an initial velocity of 48 km/s in the same direction as the electric field, which has magnitude E= 71 N/C. What is the speed in (km/s) of the electron 3.0 ns after entering this region? How far (in microns) does the electron travel during the 3.0 ns interval?

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