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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. Total flux will be zero
Explanation: Step 1: Gauss's law relates total flux to net enclosed charge. Step 2: If net charge is zero, total flux is zero even when local field exists. Step 3: Do not confuse zero total flux with zero field everywhere.
Correct answer: A. Total flux remains unchanged
Explanation: Step 1: Total flux depends on enclosed charge, not on the charge position. Step 2: The charge remains inside, so enclosed charge is unchanged. Step 3: Field distribution may change, but total flux remains the same.
Correct answer: A. Total flux remains same but field on the surface is not uniform
Explanation: Step 1: Gauss's law does not require the charge to be at the centre. Step 2: Since the charge is inside, total flux is decided by enclosed charge. Step 3: Off-centre position makes field non-uniform on the surface, so field calculation becomes harder.
Correct answer: A. Unchanged
Explanation: Step 1: Total flux depends on enclosed charge. Step 2: Changing radius does not change the charge inside. Step 3: Hence total flux remains unchanged, though field on the surface decreases.
Correct answer: A. One-sixteenth of the earlier value
Explanation: Step 1: Field due to a point charge is inversely proportional to square of distance. Step 2: Making radius four times makes square of distance sixteen times. Step 3: So field on the surface becomes one-sixteenth.
Correct answer: A. Because field decreases and enclosed charge remains the same
Explanation: Step 1: Field due to a point charge decreases with distance. Step 2: At the same time, area of the Gaussian sphere increases. Step 3: If enclosed charge is unchanged, the total effect gives the same flux.
Correct answer: A. Positive
Explanation: Step 1: Total flux is decided by the sign of net enclosed charge. Step 2: Five positive and three equal negative charges give net positive charge. Step 3: Therefore total outward flux is positive.
Correct answer: A. Negative
Explanation: Step 1: In Gauss's law, total flux depends on net charge inside. Step 2: Two positive and six negative charges give net negative charge. Step 3: Hence outward flux is negative.
Correct answer: A. Zero
Explanation: Step 1: Four positive and four equal negative charges give zero net charge. Step 2: Individual charges may create field on the surface. Step 3: But net enclosed charge is zero, so total flux is zero.
Correct answer: A. Zero
Explanation: Step 1: The outside charge can make the field strong on the surface. Step 2: But it is not enclosed by the surface. Step 3: Its lines enter and leave equally, so total flux remains zero.
Correct answer: A. Field is not simple or uniform on the chosen surface
Explanation: Step 1: Gauss's law gives total flux. Step 2: To find field, the field must be expressible simply on the surface. Step 3: Without symmetry, direct field calculation is difficult.
Correct answer: A. Because field magnitude and direction on the surface are not simple
Explanation: Step 1: Validity of the law and ease of calculation are different. Step 2: In asymmetry, field can vary from point to point. Step 3: Without symmetry, isolating field from flux becomes difficult.
Correct answer: A. Because electric field is perpendicular to the area vector of the ends
Explanation: Step 1: Field of an infinite line charge is radial. Step 2: Area vectors of flat ends of the cylinder are along the axis. Step 3: These directions are perpendicular, so end flux is zero.
Correct answer: A. Because all points on the curved surface are at the same distance from the line
Explanation: Step 1: An infinite line charge has cylindrical symmetry. Step 2: Every point on a coaxial cylindrical surface is equally distant from the axis. Step 3: Hence field magnitude is taken the same there.
Correct answer: A. One-fifth of the earlier value
Explanation: Step 1: Field of an infinite line charge is inversely proportional to distance. Step 2: If distance becomes five times, field becomes five times smaller. Step 3: Hence it becomes one-fifth.
Correct answer: A. One-twenty-fifth of the earlier value
Explanation: Step 1: Field of a point charge varies inversely with square of distance. Step 2: Making distance five times makes square of distance twenty-five times. Step 3: So field becomes one-twenty-fifth.
Correct answer: A. Inverse square, simple inverse, distance independent
Explanation: Step 1: For point charge, spherical area grows with square of distance. Step 2: For line charge, cylindrical curved area grows with distance. Step 3: For infinite sheet, field is independent of distance.
Correct answer: A. Because electric field is parallel to the side surface
Explanation: Step 1: Field of an infinite sheet is perpendicular to the sheet. Step 2: For the side surface of the pillbox, this field runs along the surface. Step 3: Since it does not cross the side surface, side flux is zero.
Correct answer: A. Because field is perpendicular to the sheet on both sides
Explanation: Step 1: An infinite uniform sheet has the same symmetry on both sides. Step 2: The field is perpendicular on both sides. Step 3: Therefore both flat faces of the pillbox contribute to flux.
Correct answer: A. Unchanged
Explanation: Step 1: Field of an infinite plane sheet does not depend on distance. Step 2: Its value is connected to surface charge density. Step 3: Since density is unchanged, increasing distance does not change the field.
Correct answer: A. Three times
Explanation: Step 1: Field of an infinite sheet is proportional to surface charge density. Step 2: Distance effect does not appear in this ideal case. Step 3: If density becomes three times, field also becomes three times.
Correct answer: A. Symmetry explains cancellation of field at every interior point
Explanation: Step 1: The Gaussian surface inside encloses zero charge. Step 2: Zero total flux alone does not always prove zero field everywhere. Step 3: Spherical symmetry shows that the field inside is zero at every point.
Correct answer: A. Because an external Gaussian sphere encloses all charge and symmetry is spherical
Explanation: Step 1: A spherical shell shows spherical symmetry from outside. Step 2: An outside Gaussian sphere encloses the entire charge. Step 3: Hence outside field is like that of a point charge at the centre.
Correct answer: A. It increases directly with distance
Explanation: Step 1: An inner Gaussian surface encloses only the charge within it. Step 2: Enclosed charge grows as cube of distance and surface area as square. Step 3: Therefore field inside is proportional to distance.
Correct answer: A. Because inside field is proportional to distance and distance at centre is zero
Explanation: Step 1: Inside a uniformly charged solid sphere, field increases with distance from centre. Step 2: At the centre, distance is zero. Step 3: Therefore electric field at the centre is zero.
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