Gauss' theorem
ICSE · Class 12 · Physics
Flashcards for Gauss' theorem — ICSE Class 12 Physics. Quick Q&A cards covering key concepts, definitions, and formulas.
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State the area vector.
Answer
Formula: A = A · n̂ Meaning: The area vector has magnitude equal to the area and direction along the outward normal. Unit: m² for area magnitude. Quick example: For a plane surface, the vector points …
A plane surface of area 5 m² has its normal at 60° to a uniform electric field of 20 N/C. Find the electric flux.
Answer
Given: E = 20 N/C, A = 5 m², θ = 60° Formula: Φ_E = EA cosθ Step 1: cos 60° = 1/2 Step 2: Φ_E = 20 × 5 × (1/2) N·m²/C Step 3: Φ_E = 50 N·m²/C Answer: 50 N·m²/C…
What is the electric flux through a plane surface parallel to the electric field?
Answer
For a plane surface parallel to the field, θ = 90°. Formula: Φ_E = EA cosθ Since cos 90° = 0, the flux is 0. Physical meaning: field lines do not pass through the surface normally. Example: A surface …
State the definition and SI unit of electric flux.
Answer
Definition: Φ_E = ∫ E · dA for an open surface, and Φ_E = ∮ E · dA for a closed surface. Meaning: Electric flux is a measure of the number of field lines passing through a surface. SI unit: N·m²/C or …
A closed surface encloses a charge of 3 μC. Find the net electric flux through it.
Answer
Given: q = 3 μC = 3 × 10^-6 C Formula: Φ_E = q/ε₀ Take ε₀ ≈ 8.85 × 10^-12 C² N^-1 m^-2 Step 1: Φ_E = (3 × 10^-6)/(8.85 × 10^-12) N·m²/C Step 2: Φ_E ≈ 3.39 × 10^5 N·m²/C Answer: 3.39 × 10^5 N·m²/C…
State Gauss' theorem in integral form.
Answer
Formula: Φ_E = ∮ E · dA = q/ε₀ Meaning: The net electric flux through any closed surface equals 1/ε₀ times the net charge enclosed. Condition: It applies to a closed surface. Quick example: If enclose…
A point charge of 2 μC is enclosed by a spherical Gaussian surface. Find the flux through the surface.
Answer
Given: q = 2 μC = 2 × 10^-6 C Formula: Φ_E = q/ε₀ Step 1: Φ_E = (2 × 10^-6)/(8.85 × 10^-12) N·m²/C Step 2: Φ_E ≈ 2.26 × 10^5 N·m²/C Answer: 2.26 × 10^5 N·m²/C…
Why does a charge outside a closed surface produce zero net flux through that surface?
Answer
A charge outside the surface sends field lines into the surface at one part and out at another part. The inward and outward contributions cancel in the total flux. So, the net flux due to charge outsi…
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