CP An electron is projected with an initial speed v_o = 1.60 times 10^6 m/s into
ID: 3279267 • Letter: C
Question
CP An electron is projected with an initial speed v_o = 1.60 times 10^6 m/s into the uniform field between two parallel plates (Fig. E21.29). Assume that the field between the plates is uniform and directed vertically downward and that the field outside the plates is zero. The electron enters the field at a point midway between the plates. (a) If the electron just misses the upper plate as it emerges from the field, find the magnitude of the electric field. (b) Suppose that the electron in Fig. E21.29 is replaced by a proton with the same initial speed v_o. Would the proton hit one of the plates? If not, what would be the magnitude and direction of its vertical displacement as it exits the region between the plates? (c) Compare the paths traveled by the electron and the proton, and explain the differences. (d) Discuss whether it is reasonable to ignore the effects of gravity for each particle.Explanation / Answer
Given,
v = 1.6 x 10^6 m/s
a)v = d/t => t = d/v
t = 0.02/1.6 x 10^6 = 1.25 x 10^-8 s
we know from eqn of motion
s = ut + 1/2 at^2
0.01 = a (1.25 x 10^-8) => a = 6.4 x 10^13 m/s^2
the electric force is the net force so
Fnet = ma = e E
E = ma/e = 9.1 x 10^-31 x 6.4 x 10^13/1.6 x 10^-19 = 364 N/C
Hence, E = 364 N/C.
b)The proton will be able to hit the plates.
c)The path travelled will be different because of polarity and mass.
d)Yes since the net force acting between the plates is force due to presence of enetric field.