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SubjectsPhysics
गाउस का नियम और इसके अनुप्रयोग
In this Class 12 Physics topic from Chapter 1, Electric Charges and Fields, students learn how electric flux is related to the net charge enclosed by a closed surface through Gauss’s law. The topic develops the idea of Gaussian surfaces, uses symmetry to simplify electric-field calculations, and applies the law to charged spherical shells, uniformly charged spheres, infinite line charges, and plane sheets. It also helps students understand the electric field inside conductors and choose suitable surfaces for solving electrostatic problems.
Correct answer: A. Equal magnitude positive charge
Explanation: Step 1: Negative charge is induced on the inner surface to balance the positive cavity charge. Step 2: The conductor was initially neutral overall. Step 3: Therefore equal positive charge appears on the outer surface.
Correct answer: A. It remains zero
Explanation: Step 1: A nearby outside charge can make field on the surface highly non-uniform. Step 2: Still, it is not enclosed by the closed surface. Step 3: Therefore its net contribution to total flux remains zero.
Correct answer: A. Positive
Explanation: Step 1: Lines leaving indicate positive outward flux. Step 2: Lines entering contribute negative flux. Step 3: Since leaving is greater, net flux and enclosed charge are positive.
Correct answer: A. There is net negative charge inside
Explanation: Step 1: Entering lines are negative for outward flux. Step 2: If their contribution is larger, total flux is negative. Step 3: Hence net enclosed charge is negative.
Correct answer: A. Symmetry so that field can be treated simply on the surface
Explanation: Step 1: Total flux is an overall surface sum of electric field. Step 2: To isolate field, its value or direction must be simple over the surface. Step 3: Symmetry provides this simplification.
Correct answer: A. In electrostatics, both are consistent with each other
Explanation: Step 1: Both laws deal with electric field of stationary charges. Step 2: Applying Gauss's law to a point charge gives a result consistent with Coulomb's law. Step 3: Treat them as consistent, not contradictory.
Correct answer: A. Three times
Explanation: Step 1: In Gauss's law, total flux is proportional to enclosed charge. Step 2: Since permittivity is unchanged, only charge change matters. Step 3: Tripling enclosed charge triples total flux.
Correct answer: A. It remains unchanged
Explanation: Step 1: Total flux depends on net enclosed charge. Step 2: Rearranging charges may change field distribution on the surface. Step 3: But if net enclosed charge is same, total flux remains same.
Correct answer: A. Because total flux is decided by enclosed charge, not area
Explanation: Step 1: Gauss's law connects total flux through a closed surface to enclosed charge. Step 2: Changing area may alter local field values. Step 3: Still, if enclosed charge is same, total flux remains same.
Correct answer: A. Only the inside positive charge
Explanation: Step 1: In Gauss's law, total flux is decided only by enclosed charge. Step 2: Outside charges may change field at the surface. Step 3: But they do not change total flux.
Correct answer: A. No, excess charge can reside on the surface
Explanation: Step 1: In electrostatic equilibrium, field inside a conductor is zero. Step 2: This does not mean the conductor has no charge. Step 3: Excess charge can reside on its surface.
Correct answer: A. It becomes one-fourth
Explanation: Step 1: Outside a spherical conductor, field behaves as if total charge is at the centre. Step 2: Like a point charge, it follows inverse-square dependence. Step 3: Doubling distance makes the field one-fourth.
Correct answer: A. Field remains zero
Explanation: Step 1: In electrostatic equilibrium, field at every interior point of a conductor is zero. Step 2: Changing radius of an internal Gaussian surface does not create enclosed net charge. Step 3: Therefore field remains zero.
Correct answer: A. Which charge is enclosed inside the Gaussian surface
Explanation: Step 1: Gauss's law starts with enclosed charge. Step 2: Outside charges do not change total flux. Step 3: So first decide which charges are inside the surface.
Correct answer: A. Because Gauss's law relates total flux through a closed surface
Explanation: Step 1: In Gauss's law, the surface completely encloses a volume. Step 2: Only for a closed surface is enclosed charge clearly defined. Step 3: Hence the law is not directly used in enclosed-charge form for an open surface.
Correct answer: A. Point charge, infinite line charge, and infinite plane sheet
Explanation: Step 1: A point charge has spherical symmetry. Step 2: An infinite line has cylindrical symmetry. Step 3: An infinite sheet has plane symmetry, so a pillbox is useful.
Correct answer: A. Count only the net charge inside the Gaussian surface
Explanation: Step 1: In Gauss's law, total flux is decided by enclosed charge. Step 2: Outside charges may create field on the surface but do not change total flux. Step 3: Always count the net charge inside the Gaussian surface.
