One way to make a uniform electric field is to use what is known as a parallel-p
ID: 2003192 • Letter: O
Question
One way to make a uniform electric field is to use what is known as a parallel-plate capacitor. To make one, you take two metal cookie sheets from your kitchen, and place them parallel to one another, separated by a distance of 18.0 cm. Then, you connect the positive terminal of a 9-volt battery to the top cookie sheet, so that it becomes positively charged, and you connect the negative terminal of the same battery to the bottom cookie sheet, so that the bottom cookie sheet becomes negatively charged. In the picture, the top cookie sheet is drawn in red (positive) and the bottom cookie sheet is drawn in blue (negative). Note that the electric field between the cookie sheets points from the positive sheet to the negative sheet, and has a magnitude of the battery voltage (9 V) divided by the distance between the cookie sheets. An electron (in blue) is given an initial velocity horizontally. The initial velocity of the electron is directed along the line parallel to the cookie sheets and halfway between them. After traveling a horizontal distance of d = 30.0 cm, and the appropriate distance vertically, the electron runs into one of the cookie sheets (you should know which one). Calculate the magnitude of the acceleration of the electron, solely because of the uniform electric field between the two cookie sheets. Note that, once you see the answer, it should be obvious to you why we can neglect the acceleration due to gravity in this problem, m/s/s Calculate the time it takes for the electron to reach the cookie sheet, s Calculate the electron's initial velocity, m/sExplanation / Answer
a) a= F/m = qE/m = [q(V/d)]/m = qV/md = (1.6*10^-19*9)/(9.1*10^-31*0.18) = 8.8*10^12 m/s^2
directed downward
b) h = viy*t +1/2at^2
-0.09 = 0*t – 1/2*(8.8*10^12)*t^2 => t= 1.43*10^-7 s
c) d= vix*t
0.30 = vix*(1.43*10^-7) => vix = 2.1*10^9 m/s
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