Cathode-ray tubes (CRTs) are often found in oscilloscopes and computer monitors.

Question

Cathode-ray tubes (CRTs) are often found in oscilloscopes and computer monitors. In the figure (Figure 1) an electron with an initial speed of 6.30

Cathode-ray tubes (CRTs) are often found in oscilloscopes and computer monitors. In the figure (Figure 1) an electron with an initial speed of 6.30 times 106m/s is projected along the axis midway between the deflection plates of a cathode-ray tube. The potential difference between the two plates is 24.0V and the lower plate is the one at higher potential. What is the magnitude of the force on the electron when it is between the plates? What is the magnitude of the acceleration of the electron when acted on by the force in part (a)? How far below the axis has the electron moved when it reaches the end of the plates? At what angle with the axis is it moving as it leaves the plates?

Explanation / Answer

E = V/d = 24/0.02 = 1200 V/m

force = eE = 1.602*10^-19 * 1200 = 1.92*10^-16 N

acceleration = F/m = 1.92*10^-16/ 9.11*10^-31 = 2.11* 10^14 m/s^2

force will act downward onelectron.

horizontal velocity will remain same.

t = 0.06/v0 = 9.52*10^-9 sec

vy = 0 + 2.11*10^14 * 9.52*10^-9 = 2*10^6 m/s

distance covered in y direction s.

vy^2 = 0 + 2*ay*s

s= vy^2/(2*a) = 0.95 cm

tan theta = vy/v0 = 2/6.3

theta (with x axis) = 17.61 degree

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