Muft Shiksha™ एक 100% Free Education Portal है 🇮🇳, जिसका उद्देश्य Class 9–12 के हर विद्यार्थी तक High-Quality Education को पूरी तरह मुफ्त पहुँचाना है। 🇮🇳 हम मानते हैं कि अच्छी शिक्षा किसी student की आर्थिक स्थिति पर निर्भर नहीं होनी चाहिए। 🇮🇳 हर विद्यार्थी को वही Quality Study Material, MCQs, Quizzes, Exam Preparation, Concept-Based Learning और Bilingual Support मिलना चाहिए, जो आमतौर पर महंगी Coaching या Premium Platforms में मिलता है। Muft Shiksha™ 🇮🇳 इसी सोच के साथ बनाया गया है
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. Because enclosed net charge remains the same
Explanation: Step 1: Total flux depends on enclosed charge. Step 2: If the charge remains inside, the value of enclosed charge does not change. Step 3: Position change may change distribution of flux, not total flux.
Correct answer: A. Because all faces of the cube are symmetric with respect to the centre
Explanation: Step 1: The charge is exactly at the centre. Step 2: All six faces of the cube are equally placed with respect to that charge. Step 3: Therefore total flux is equally divided among the six faces.
Correct answer: C. One sixth
Explanation: Step 1: A cube has six equal faces. Step 2: Since the charge is at the centre, symmetry gives equal flux through all faces. Step 3: Therefore one face gets one sixth of total flux.
Correct answer: B. Total flux will be negative
Explanation: Step 1: According to Gauss's law, sign of total flux is linked with sign of enclosed net charge. Step 2: Negative enclosed charge means field lines are net inward. Step 3: Therefore total flux is negative.
Correct answer: A. To decide the sign of flux systematically
Explanation: Step 1: For each small part of a closed surface, area vector is taken outward. Step 2: This makes outgoing flux positive and incoming flux negative. Step 3: This convention is very useful in sign-based questions.
Correct answer: A. Since electric field inside is zero, flux through an internal Gaussian surface is zero
Explanation: Step 1: Inside a conductor at electrostatic equilibrium, electric field is zero. Step 2: A closed Gaussian surface inside has zero net flux. Step 3: By Gauss's law, excess charge enclosed by it is zero.
Correct answer: B. Outgoing lines are more
Explanation: Step 1: Outward direction is taken positive for a closed surface. Step 2: Positive net flux means outgoing contribution is greater. Step 3: Thus outgoing lines are more than incoming lines.
Correct answer: B. Toward the wire
Explanation: Step 1: Field lines go toward negative charge. Step 2: For a long negative wire, symmetry makes field radial toward the wire. Step 3: Positive wire gives outward field and negative wire gives inward field.
Correct answer: A. Away from the sheet
Explanation: Step 1: Field lines emerge from positive charge. Step 2: For an infinite sheet, field is normal to the sheet and outward on both sides. Step 3: Remember directions separately for positive and negative sheets.
Correct answer: B. Toward the sheet
Explanation: Step 1: Field lines go toward negative charge. Step 2: On both sides of a negative infinite sheet, field points toward the sheet. Step 3: First check the sign of charge while deciding direction.
Correct answer: A. Identify symmetry, choose Gaussian surface, find enclosed charge
Explanation: Step 1: First identify the symmetry of charge distribution. Step 2: Then choose a suitable Gaussian surface and find enclosed charge. Step 3: Finally relate total flux with electric field.
Correct answer: A. Net charge enclosed inside the closed surface
Explanation: Step 1: Gauss's law connects total flux through a closed surface with net enclosed charge. Step 2: Shape or colour does not decide the total flux. Step 3: In such questions, identify enclosed charge first.
Correct answer: A. It becomes double
Explanation: Step 1: Total flux is proportional to enclosed charge. Step 2: Doubling enclosed charge doubles the net source. Step 3: Therefore total flux also doubles.
Correct answer: A. It remains unchanged
Explanation: Step 1: According to Gauss's law, total flux depends on enclosed charge. Step 2: Changing shape may alter field distribution on the surface. Step 3: But if enclosed charge remains the same, total flux is unchanged.
Correct answer: A. Zero
Explanation: Step 1: The outside charge can create field on the surface. Step 2: Its lines both enter and leave the closed surface. Step 3: Since enclosed charge is zero, total flux is zero.
Correct answer: A. Positive
Explanation: Step 1: Total flux depends on the sign of net enclosed charge. Step 2: Two positive and one equal negative charge give a positive net charge. Step 3: Hence total outward flux is positive.
Correct answer: A. Negative
Explanation: Step 1: In Gauss's law, total flux through a closed surface is decided by net enclosed charge. Step 2: One positive and two equal negative charges give a negative net charge. Step 3: So total outward flux is negative.
Correct answer: A. Because it allows the electric field to be treated simply on the surface
Explanation: Step 1: Gauss's law is true for every closed surface. Step 2: Calculation becomes easy when the chosen surface matches the symmetry. Step 3: Therefore identify symmetry first.
Correct answer: A. Because a point charge has spherical symmetry
Explanation: Step 1: The field from a point charge spreads symmetrically in all directions. Step 2: Every point on a centered sphere is at the same distance from the charge. Step 3: Therefore field magnitude is the same on the surface.
Correct answer: A. Because a line charge has cylindrical symmetry
Explanation: Step 1: Around an infinite line charge, the field is radial. Step 2: A coaxial cylinder matches this symmetry. Step 3: Therefore field magnitude can be treated as same on the curved part.
Correct answer: A. Because the field is perpendicular and equal on both sides of the sheet
Explanation: Step 1: For an infinite sheet, field is perpendicular to the surface. Step 2: Equal behavior on both sides makes the pillbox useful. Step 3: Remember this surface for plane symmetry.
Correct answer: A. Because a Gaussian surface inside encloses no charge
Explanation: Step 1: Charge of a spherical shell lies on its surface. Step 2: A Gaussian surface inside the shell encloses zero charge. Step 3: By symmetry, the field inside becomes zero.
Correct answer: A. Like the field of the same total charge placed at the centre
Explanation: Step 1: A spherical shell has spherical symmetry. Step 2: A Gaussian surface outside encloses the whole charge. Step 3: The outside field behaves like that of a point charge at the centre.
Correct answer: A. Because free charges move until the net internal field becomes zero
Explanation: Step 1: Free charges in a conductor can move easily. Step 2: If an internal field exists, they keep moving. Step 3: Equilibrium is reached only when the internal field becomes zero.
Correct answer: A. Because a small Gaussian surface inside must enclose zero net charge
Explanation: Step 1: Inside a conductor in electrostatic equilibrium, electric field is zero. Step 2: For a Gaussian surface inside, total flux is zero. Step 3: So no excess net charge remains in the bulk; it resides on the surface.
