The disk in the figure (Figure 1) is uniformly charged to 7.2 C and has area 0.1

Question

The disk in the figure (Figure 1) is uniformly charged to 7.2 C and has area 0.19 m2 .

Part A

Find the approximate field strength 1 mm from the disk, not near an edge.

Express your answer using two significant figures.

Part B

Find the approximate field strength 2.9 m from the disk.

Express your answer using two significant figures.

Figure 1 of 1

The disk in the figure (Figure 1) is uniformly charged to 7.2 C and has area 0.19 m2 .

Part A

Find the approximate field strength 1 mm from the disk, not near an edge.

Express your answer using two significant figures.

E1 = N/C

Part B

Find the approximate field strength 2.9 m from the disk.

Express your answer using two significant figures.

E2 = N/C

Figure 1 of 1

Explanation / Answer

field due to charged disk:

E = 2pi sigma k [ 1 - (x / sqrt(x^2 + R^2) ) ]

sigma = (7.2 / 0.19) uC/ m^2 = 37.89 x 10^-6 C /m^2

x = 1 x 10^-3 m

pi r^2 = 0.19

r = 0.246 m

E = (2 x pi x 37.78 x 10^-6 ) [ 1 - (0.001 / sqrt(0.001^2 + 0.246^2) ]

E = 2.36 x 10^-4 N/C

B) now x = 2.9 m

E = (2 x pi x 37.78 x 10^-6 ) [ 1 - (2.9/ sqrt(2.91^2 + 0.246^2) ]

E = 8.495 x 10^-7 N/C

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