She wants you to calculate the coulomb force and then the acceleration. Then you

Question

She wants you to calculate the coulomb force and then the acceleration. Then you use that to calculate the time to travel 1 meter with initial velocity zero.
a)so first calculate coulomb force
b) calculate acceleration
c) calculate time to travel 1 meter
d) calculate time to travel the full distance

the correct answer is 5x10^-9 seconds

PHYS222 Quiz#3 motion in a uniform E-field k=9x109 N. m2/C2 e=1.6x10-19 c E0 = 8.85 x 10-12 c2/(N·m2) me = 9.1 X 10-31 kg An electron is projected horizontally into the uniform electric field E - 400 N/C directed vertically downward between two parallel plates as shown in the figure. The plates are 2 m apart and are of length 4 m. The initial velocity of this electron is v, 8 X 10a m/s to the right (positive x-direction). W =2m L=4m 1. The two parallel plates in the above figure are oppositely charged metallic plates. Which one (upper or lower one) is positively charged? 2. The electron passes through the chamber without colliding into either of the conducting plates. What is the time the electron spends between the plates?

Explanation / Answer

1)The electric field is directed downwards. We know that the electric field lines originate from the positive charge and terminate on negative charge. So the UPPER ONE IS POSITIVELY CHARGED.

2)Let the required time be t.

from the defination of speed:

s = d/t => t = d/s

t = 4 m/8 x 10^8 m/s = 5 x 10^-9 s

Hence, t = 5 x 10^-9 s = 5 nano second.

a)Coulomb force is not required to be calculated here. But yes the electric force is acting on the electron with magnitude

F = q E

F = 1.6 x 10^-19 x 400 = 6.4 x 10^-17 N

Hence, F = 6.4 x 10^-17 N

b)let a be the acceleration. The net force acting on the electrons is the elecrtic force only thats why it passes undeflected, so

F(electric) = q E = ma

a = q E/m = 1.6 x 10^-19 x 400 / 9.1 x 10^-31 = 7.03 x 10^13 m/s^2

Hence, a = 7.03 x 10^13 m/s^2

c)time to trave; 1 sec is:

we know from eqn of motion

S = ut + 1/2 at^2

1 = 0 + 0.5 x 7.03 x 10^13 x t^2

1 = 3.52 x 10^13 t^2

t = sqrt (1/ 3.52 x 10^13 ) = 1.69 x 10^-7 s

Hence, t = 1.69 x 10^-7 s

d)Calculated in (2)

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