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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. Positive charge is a source of field lines
Explanation: Step 1: Field lines emerge from positive charge. Step 2: Symmetry of an infinite sheet is same on both sides. Step 3: Hence field points away from the sheet on both sides.
Correct answer: A. Toward the sheet
Explanation: Step 1: Field lines go toward negative charge. Step 2: Symmetry of an infinite sheet is same on both sides. Step 3: Therefore field points toward the sheet on both sides.
Correct answer: A. Radially outward from the wire
Explanation: Step 1: Field lines emerge from a positive line charge. Step 2: Cylindrical symmetry makes the direction radial and perpendicular to the wire. Step 3: For positive wire, remember outward direction.
Correct answer: A. Lack of symmetry makes it difficult to separate field from flux
Explanation: Step 1: Gauss's law gives correct total flux. Step 2: To find field, simple behaviour of field on the surface is needed. Step 3: In irregular distributions, this simplicity is absent.
Correct answer: A. Three times
Explanation: Step 1: Net flux is proportional to enclosed net charge. Step 2: Surface area does not independently decide net flux. Step 3: Since enclosed charge is tripled, net flux becomes three times.
Correct answer: A. Negative
Explanation: Step 1: Add the charges enclosed by the closed surface. Step 2: Positive two and negative five give a negative net charge. Step 3: Negative enclosed charge gives negative net flux.
Correct answer: A. Net charge inside is zero
Explanation: Step 1: Outgoing lines give positive flux and incoming lines give negative flux. Step 2: If both are equal, net flux is zero. Step 3: Zero net flux means zero enclosed net charge.
Correct answer: A. It remains same
Explanation: Step 1: Net flux depends on enclosed net charge. Step 2: External charges can change field distribution on the surface. Step 3: If enclosed net charge remains same, net flux remains same.
Correct answer: A. Negative
Explanation: Step 1: For a closed surface, outward normal is taken positive. Step 2: If field is opposite to it, the field is entering that part. Step 3: Therefore flux through that part is negative.
Correct answer: A. Zero
Explanation: Step 1: Only the normal component crossing the surface contributes to flux. Step 2: Tangential component runs along the surface and does not pass through it. Step 3: Therefore flux is zero.
Correct answer: A. Tangential field would move free charges
Explanation: Step 1: Free charges in a conductor can move easily. Step 2: Any field component along the surface would keep them moving. Step 3: Hence in equilibrium, the outside field is normal to the surface.
Correct answer: A. Both behave like total charge placed at the centre
Explanation: Step 1: In both cases, an outside Gaussian surface encloses the whole charge. Step 2: Due to spherical symmetry, outside field is like a point charge. Step 3: The main difference lies in the field inside the sphere.
Correct answer: A. In conductor field is zero, in solid non-conductor it can increase from centre
Explanation: Step 1: In a conductor, excess charge stays on surface and inside field is zero. Step 2: In a solid non-conductor, charge is spread through volume. Step 3: Therefore field inside the non-conductor can increase outward from centre.
Correct answer: A. Zero
Explanation: Step 1: Net flux is decided by enclosed net charge. Step 2: No charge is enclosed, so enclosed charge is zero. Step 3: External lines enter and leave equally, so net flux is zero.
Correct answer: A. More lines leave than enter
Explanation: Step 1: For a closed surface, outward direction is taken positive. Step 2: Positive net flux means outgoing contribution is greater. Step 3: It indicates positive net charge inside.
Correct answer: A. Field lines are net entering the surface
Explanation: Step 1: For a closed surface, outward direction is positive. Step 2: Negative net flux means inward contribution is greater. Step 3: This indicates negative net charge inside.
Correct answer: A. Lines that enter also leave
Explanation: Step 1: Field lines from an outside charge can cross the closed surface. Step 2: As many lines enter as leave. Step 3: Entry and exit cancel, giving zero net flux.
Correct answer: A. When the new surface preserves symmetry and enclosed charge correctly
Explanation: Step 1: Gaussian surface is a calculation tool, not necessarily a physical object. Step 2: If the new surface uses symmetry correctly, the result can remain same. Step 3: Do not spoil enclosed charge and field simplicity.
Correct answer: A. Flux calculation becomes simple
Explanation: Step 1: For normal field, the full field component crosses the surface. Step 2: If magnitude is also simple, total flux is easy to find. Step 3: This is the aim of choosing a proper Gaussian surface.
Correct answer: A. Zero
Explanation: Step 1: Flux comes from relation between electric field and area. Step 2: If electric field itself is zero, no field crosses the surface. Step 3: Therefore flux through that part is zero.
Correct answer: A. Both are zero
Explanation: Step 1: A dipole has equal positive and negative charges. Step 2: If the whole dipole is inside, enclosed net charge is zero. Step 3: By Gauss's law, net flux is also zero.
Correct answer: A. Negative
Explanation: Step 1: In Gauss's law, only charge inside the surface is counted. Step 2: Negative charge is inside and positive charge is outside. Step 3: Therefore enclosed net charge and net flux are negative.
Correct answer: A. Positive
Explanation: Step 1: Net flux through a closed surface is decided by net enclosed charge. Step 2: Only positive charge is inside, so enclosed charge is positive. Step 3: Hence net flux is positive.
Correct answer: A. Charges placed outside the closed surface
Explanation: Step 1: Net flux is based on enclosed net charge. Step 2: Outside charges can change local field on the surface. Step 3: But they do not change net flux, so do not add them to enclosed charge.
Correct answer: A. Identify the closed surface and its net enclosed charge
Explanation: Step 1: Gauss's law relates net flux to enclosed charge. Step 2: So first identify the closed surface and which charges are inside. Step 3: Then use symmetry to choose surface and calculate field.
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