The total electric field at a point on the axis of a uniformly charged disk, whi

Question

The total electric field at a point on the axis of a uniformly charged disk, which has a radius R and a uniform charge density of , is given by the following expression, where x is the distance of the point from the disk.

Ex = 2ke

1

Consider a disk of radius R = 2.88 cm having a uniformly distributed charge of +5.43 µC.

(a) Using the expression above, compute the electric field at a point on the axis and 2.73 mm from the center.

and

(c) Using the first expression above, compute the electric field at a point on the axis and 27.3 cm from the center of the disk.

Explanation / Answer

a) = Q/pi*R^2 = 5.43*10^-6/(pi*0.0288^2) = 0.002084 C/m^2

Ex = 2ke[ 1 - x/sqrt(R^2 + x^2)]

= (2*9*10^9*0.002084)*[1 - 2.73*10^-3/sqrt(0.0288^2 + 0.00273^2)] = 1.07*10^8 N/C

b) Ex = 2ke[ 1 - x/sqrt(R^2 + x^2)]

= (2*9*10^9*0.002084)*[1 - 27.3*10^-2/sqrt(0.0288^2 + 0.273^2)] = 6.5*10^5 N/C

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