Electron's Speed in Field and Charge

[Soaring Crane]

Homework Statement

An electron is released from rest in a uniform electric field of 1.25 kN/C. After 20 ns, the electron's speed will be approximately


a. 2.5 x 10^-5 m/s

b. 3.9 x 10^3 m/s

c. 3.0 x 10^8 m/s

d. 2.5 x 10^3 m/s

e. 4.4 x 10^6 m/s

Homework Equations

Vector E = (m_e*a)/q_e

v_f = v_i +a*t

The Attempt at a Solution

a = (E*q_e)/m_e = [(1250 N/C)*(1.60*10^-19 C)]/(9.11*10^-31 kg) = 2.1954*10^14 m/s^2

v_f = v_i +a*t, where v_i = 0 m/s

v_f = a*t = (20*10^-9 s)*(2.1954*10^14 m/s^2) = 4.39*10^6 m/s (E.) ?

Homework Statement

How many electrons must be transferred to a body to produce a charge of 125 nC?

a. 1.25 10^-7
b. 7.81 10^11
c. 1.28 10^12
d. 3.45 10^11

Homework Equations

Total q / q_e = # of electrons

The Attempt at a Solution

(125*10^-9 C)/(1.60*10^-19 C) = 7.813*10^11 electrons ?

Thanks.

 

[Kurdt]

Both correct as far as I can see.

 

[m2003]

I would like to point out that the given options for the electron's speed are not consistent with the given electric field. The correct answer should be in the range of 4.39 x 10^6 m/s, which is option e. Additionally, it is important to note that the speed of an electron in a uniform electric field will depend on its initial velocity and the direction of the electric field.

For the second homework statement, the correct answer would be option b, 7.81 x 10^11 electrons. This can be calculated by dividing the total charge (125 nC) by the charge of one electron (1.60 x 10^-19 C). It is important to note that the number of electrons transferred to a body will depend on the material and its properties, so the answer may vary in different situations.