Question

Two 10-cm-diameter charged disks face each other,

25 cm apart. Both disks are charged to - 30 nC .

Part A

What is the electric field strength between the disks, along their common axis, at the midpoint between the two disks?

Part B

What is the electric field strength between the disks, along their common axis, at a point 5.0 cm from one disk?

Answer 1

A.

At the midpoint the electric fields are equal and opposite so that net electric field is ZERO

B.

Electric field due to finite disk:

E= (/2_o)*[1-(x / √(x²+R²)] ------1

= q/ 3.14 R² = 30×10^(−9)÷(3.14×0.05²) = 3.82*10^-6C/m²

E at 0.05 m:

E1=(3.82×10^(−6)÷(2×8.85×10^(−12)))×(1−(0.05÷√(0.05²+0.05²)))

E1=63211.98 N/C

E at 0.20 m:

E2=(3.82×10^(−6)÷(2×8.85×10^(−12)))×(1−(0.20÷√(0.20²+0.05²)))

E2=6443.82 N/C

Net electric fiel at 5.0 cm is

E1-E2 =63211.98 -6443.82= 56768.16 N/C