Question

In the 2007 film Bladerunner, there is a scene in which Decker is scouring security footage and utterly abuses the magical “enhance image” ability that seems to only exist in movies and TV. The monitor he is using, however, is a CRT (cathode ray tube) monitor, which works by firing a beam of electrons from a region in the back of the monitor forward to the screen. In such a device, the electron is accelerated through a voltage of about 7.0 ?? over a very small distance.

a. If the electron begins, on average, at rest (the velocities of individual electrons will vary, but their relative randomization will ensure that the average starting velocity of an electron will be near zero), find the speed at which the electron is moving when it has been fully accelerated.

b. If the monitor is oriented so that the electron beam is travelling directly north and a magnetic field is introduced that has a magnitude of |?| = 0.02 ? and points directly west, what is the acceleration (magnitude and direction) experienced by an electron?

Answer 1

Sol: Here accelerating voltage V = 7.0kV = 7000V

(a) Now if final speed is v then according to conservation of energy -

or

(b) Here B = 0.02T hence force on electron is given by-

directed vertically downward

Hence acceleration is given as-

And it is directed vertically down ward.