Electrons in a particle beam each have a kinetic energy of 4.0 × 10 −17 J. What is the magnitude of the electric field that will stop these electrons in a distance of 0.3 m? ( e = 1.6 × 10 −19 C)

-833.3 N/C

Explanation:

Kinetic energy, K, in terms of electric field, E, is given as:

K = qEr

q = charge = e = 1.6 × 10⁻¹⁹C

E = Electric field

r = distance = 0.3m

The electric field can be gotten by making E subject of formula:

E = K/(qr)

The electeic field needed to stop the electrons must be equal in magnitude to the electric field carried by these electrons:

E = (4.0 × 10⁻¹⁷)/(-1.6 × 10⁻¹⁹ * 0.3)

E = -833.3 N/C

This is the electric field needed to stop the electrons.

The negative sign means that the electric field must be in a direction opposite to the motion of the electrons.