10. Field, Potential, and Potential Energy A uniform electric field is set up be

Question

10. Field, Potential, and Potential Energy A uniform electric field is set up between two charged parallel plates. Suppose the spacing of the plates is 10 cm and the magnitude of the electric field is 20 N/C. a) What is the direction of the electric field? Why? (b) On which side is the electric potential higher? (Left or right?) Why? (c) What is the magnitude of the potential difference AV across the plates? Hint: E--dV / dr--AV/ x when the field is constant. (d) Suppose an electron is moved from the left plate to the right plate. What is the magnitude of the change in its potential energy? Does its potential energy increase or decrease? Why? (e) Suppose an electron and a proton are released at the center point (between the plates). The electron is accelerated to the left and the proton to the right. Find the values of (i) the kinetic energies, (ii) the momenta, and (ii) the speeds of the two particles when they reach the plates.

Explanation / Answer

(A) field is away from +ve plate and toward the -ve charge.

direction-> to the right

(B) field is always from higher potential to lower potentail.

- left side  

(C) deltaV = E.d = 20 x 0.10

= 2 Volt

(D) magnitude of of change in PE = 2 eV  

it increases.

we have to work against electric force to move this.

(e) (i) KE = 1 eV = 1.6 x10^-19 J for both

(ii) p = sqrt(2 m KE)

for proton, 2.313 x 10^-23 kg m/s

for electron, 5.40 x 10^-25 kg m/s

(iii) v = momenta / m

v _proton = 13850 m/s

v_electron = 5.93 x 10^5 m/s

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