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Electric Charges and Fields

CBSE · Class 12 · Physics

Flashcards for Electric Charges and Fields — CBSE Class 12 Physics. Quick Q&A cards covering key concepts, definitions, and formulas.

75 questions20 flashcards5 concepts
20 Flashcards
Card 1Coulomb's Law

Two point charges of +3 μC and -5 μC are separated by 30 cm in air. Calculate the electrostatic force between them.

Answer

Given: q₁ = +3 μC = 3×10⁻⁶ C, q₂ = -5 μC = -5×10⁻⁶ C, r = 30 cm = 0.3 m Formula: F = k|q₁q₂|/r² Step 1: F = (9×10⁹ × 3×10⁻⁶ × 5×10⁻⁶)/(0.3)² Step 2: F = (135×10⁻³)/(0.09) = 1.5 N Since charges are opp

Card 2Electrostatic Phenomena

Why do clothes made of synthetic materials stick to our body, especially in dry weather?

Answer

This happens due to electrostatic charging by friction. When synthetic clothes rub against skin, electrons transfer between surfaces, creating opposite charges. The attractive force between these oppo

Card 3Coulomb's Law

State Coulomb's Law and write its mathematical expression with units.

Answer

Coulomb's Law: The electrostatic force between two point charges is directly proportional to the product of charges and inversely proportional to the square of distance between them. Mathematical form

Card 4Electric Field

A charge of 8 μC is placed at the origin. Find the electric field at point P(3,4) meters.

Answer

Given: q = 8 μC = 8×10⁻⁶ C, P(3,4) m Step 1: Distance r = √(3² + 4²) = 5 m Step 2: Electric field magnitude E = kq/r² = (9×10⁹ × 8×10⁻⁶)/25 = 2880 N/C Step 3: Unit vector r̂ = (3î + 4ĵ)/5 = 0.6î + 0.8

Card 5Electric Field

What is electric field? How is it different from electric force?

Answer

Electric field (E) is the region around a charge where another charge experiences force. It's defined as force per unit positive test charge: E = F/q₀. Differences: • Force depends on both source and

Card 6Superposition Principle

Three charges +2μC, -3μC, and +4μC are placed at vertices of an equilateral triangle of side 10cm. Find net force on +4μC charge.

Answer

Given: q₁ = +2μC, q₂ = -3μC, q₃ = +4μC, side = 10cm = 0.1m Step 1: F₁₃ = kq₁q₃/r² = (9×10⁹×2×4×10⁻¹²)/(0.1)² = 7.2 N (repulsive) Step 2: F₂₃ = kq₂q₃/r² = (9×10⁹×3×4×10⁻¹²)/(0.1)² = 10.8 N (attractive)

Card 7Electric Field Lines

Why do electric field lines never intersect each other?

Answer

Electric field lines never intersect because if they did, it would mean there are two different directions of electric field at the intersection point. This is impossible since electric field has a un

Card 8Work in Electric Field

A uniform electric field of 5×10³ N/C exists in a region. Calculate work done in moving a 2μC charge through 3cm in the direction opposite to field.

Answer

Given: E = 5×10³ N/C, q = 2μC = 2×10⁻⁶ C, d = 3cm = 0.03m, motion opposite to field Formula: W = qEd cosθ Step 1: Since motion is opposite to field, θ = 180°, cos180° = -1 Step 2: W = qEd cos180° = 2×

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