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A capacitor consists of two charged disks of radius 4.3 m separated by a distanc

ID: 1333229 • Letter: A

Question

A capacitor consists of two charged disks of radius 4.3 m separated by a distance s = 2 mm (see the figure). The magnitude of the charge on each disk is 45 mu C. Consider points A, B, C, and D inside the capacitor, as shown in the diagram. The distance si and the distance S2 = 0.6 mm. (Assume the + x axis is to the right, the + y axis is up, and the + z axis is out.) What is the electric field inside the capacitor? First, calculate the potential difference VB - VA. What is along this path? Next, calculate the potential difference Vc - Vb = What is Vc along this path? Finally, calculate the potential difference Va - Vc- What is along this path?

Explanation / Answer

(a)

The electric field inside is only in the x direction and is equal to

        E = q / A

          = 45 x 10-6 / (8.85 x10-12 * ) (4.32 )

         =87535 N/C

The electric files is,

          E = (87535,   0, 0)    N/C

(b)

Going from A to B,

  L= ( -0.0013, 0, 0 )   m

Therefore,

VB - VA = - 87535* (-0.0013)

               = 113.8 V

(c) Going from B to C,

L= (0,-0.0006, 0 )   m

Therefore,

            VC - VB = - 131879 * 0  

                          = 0 Volts

(d)

Going from C to A ,

L =( 0.0013 , 0.0006 , 0   )   m

Therefore,

VA - VC =  - 131879 *  0.0013  + 0 * 0.0006

              =-113.8 Volts