What is the physical principle underlying the electrostatic shielding used to protect sensitive electronic measuring instruments from external stray electrical fields?
Answer and explanation
Correct answer: D. Enclosing the device in a hollow metal cavity where internal field is strictly zero
- Step 1: Electrostatic shielding is the phenomenon of protecting a region of space from the influence of external electrostatic fields.
- Step 2: When a hollow metallic enclosure (Faraday cage) is placed in an electric field, induced charges appear on its outer surface, setting up an internal field that exactly cancels the external field.
- Step 3: Consequently, the net electric field inside the metallic cavity is identically zero (), regardless of the strength or orientation of external electric charges.
- Step 4: Sensitive instruments like galvanometers and coaxial cables are encased in metal boxes or braided metal shields for this reason.
Answer
Enclosing the instrument inside a hollow metallic conductor where the electrostatic field is strictly zero under all external conditions
Why not the others: 'Wrapping in wet cotton gauze...' does not provide electrostatic shielding; 'Subjecting to ultra-high magnetic field...' creates unwanted magnetic interference; 'Placing in glass jar...' fails because glass is an insulator and dielectric that permits electric field penetration.
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