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Question:
A hollow charged conductor has a tiny hole cut into its surface. show that the electric field in the hole is {sigma/ 2 upsilon not } n cap , where n cap is the unit vector in the outward normal direction , and sigma is the surface charge density near the hole.
Answer:

Let us consider a conductor with a cavity or a hole. Electric field inside the cavity is zero.

Let E is the electric field just outside the conductor, q is the electric charge, image202 NCERT Solutions class-12 physics Electric Charges and Field Part-2 is the charge density, and image064 NCERT Solutions class-12 physics Electric Charges and Field Part-2is the permittivity of free space.

Charge image265 NCERT Solutions class-12 physics Electric Charges and Field Part-2

According to Gauss’s law,

image266 NCERT Solutions class-12 physics Electric Charges and Field Part-2

image267 NCERT Solutions class-12 physics Electric Charges and Field Part-2

image268 NCERT Solutions class-12 physics Electric Charges and Field Part-2

Therefore, the electric field just outside the conductor isimage269 NCERT Solutions class-12 physics Electric Charges and Field Part-2. This field is a superposition of field due to the cavity image270 NCERT Solutions class-12 physics Electric Charges and Field Part-2and the field due to the rest of the charged conductorimage270 NCERT Solutions class-12 physics Electric Charges and Field Part-2. These fields are equal and opposite inside the conductor, and equal in magnitude and direction outside the conductor.

image271 NCERT Solutions class-12 physics Electric Charges and Field Part-2

image272 NCERT Solutions class-12 physics Electric Charges and Field Part-2

image273 NCERT Solutions class-12 physics Electric Charges and Field Part-2

Therefore, the field due to the rest of the conductor isimage274 NCERT Solutions class-12 physics Electric Charges and Field Part-2.

Hence, proved.

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