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.
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
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
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
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
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
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)
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
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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Sources & Official References
- NCERT Official — ncert.nic.in
- CBSE Academic — cbseacademic.nic.in
- CBSE Official — cbse.gov.in
- National Education Policy 2020 — education.gov.in
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