Inside most old fashioned ("tube") TV sets you will find two parallel charged plates designed to accelerate electrons. Let's assume an electron (mass m = 9.11 times 10-31 kg) is accelerated in the uniform field E (E = 5.40 times 103 N/C) between the plates shown in the figure. (The thickness of the plates themselves is negligible, despite how fat they might look in this picture) The electron starts from rest near the negative plate and passes through a tiny hole in the positive plate, as seen in the figure below. It exits with a kinetic energy of 1.21 times 10-17 J (which, as we will see later in this course, is enough to generate light when it finally hits the phosphors on the front screen!) In designing this system, how far apart do you need to space the two plates?
Explanation / Answer
V = (K.E)/q = 75.625 V We know, V = Ed so, d = V/E = 0.014 m = 1.4 cm = 14 mm