Current Electricity — Flashcards
Maharashtra Board · Class 12 · Physics
25 flashcards for Current Electricity (Maharashtra Board Class 12 Physics) to test yourself on key terms and facts.
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State Kirchhoff's First Law (Current Law) and explain its physical significance.
Answer
Kirchhoff's First Law states that the algebraic sum of currents at any junction in an electrical network is zero: ∑Ii = 0. Sign convention: Currents arriving at junction are positive, currents leaving…
State Kirchhoff's Voltage Law and its sign conventions.
Answer
Kirchhoff's Voltage Law states that the algebraic sum of potential differences and emfs in any closed loop is zero: ∑IR + ∑ε = 0. Sign conventions: (1) For resistors: Potential drop is negative when t…
A junction has currents: 8A entering, 3A entering, 5A leaving, and current X leaving. Find X using Kirchhoff's Current Law.
Answer
Given: Currents entering = 8A, 3A; Currents leaving = 5A, X A Applying Kirchhoff's Current Law: ∑I = 0 Current entering - Current leaving = 0 (8 + 3) - (5 + X) = 0 11 - 5 - X = 0 6 - X = 0 Therefore, …
What is the condition for balancing a Wheatstone bridge? Derive it.
Answer
Condition: P/Q = S/R or PS = QR Derivation: For balanced bridge, galvanometer current Ig = 0 From Kirchhoff's laws: Loop ABDA: -I₁P + I₂S = 0 → I₁P = I₂S ... (1) Loop BCDB: -I₁Q + I₂R = 0 → I₁Q = I₂R …
In a Wheatstone bridge, P = 100Ω, Q = 200Ω, R = 150Ω. Find S for balance condition.
Answer
Given: P = 100Ω, Q = 200Ω, R = 150Ω For balance condition: P/Q = S/R 100/200 = S/150 1/2 = S/150 S = 150/2 = 75Ω Verification: P×R = 100×150 = 15000, Q×S = 200×75 = 15000 ✓ Therefore, S = 75Ω for bala…
Explain the principle of metre bridge and derive the formula for unknown resistance.
Answer
Principle: Wheatstone bridge using uniform wire of 1m length. Unknown resistance X in left gap, known resistance R in right gap. Derivation: For balance, X/R = RAD/RDB For uniform wire: RAD = ρℓx/A, R…
In a metre bridge, balance point is at 40cm from left end. If known resistance is 6Ω, find unknown resistance.
Answer
Given: Balance point at 40cm from left, R = 6Ω ℓx = 40cm, ℓR = 100-40 = 60cm Using metre bridge formula: X = R × (ℓx/ℓR) X = 6 × (40/60) = 6 × (2/3) = 4Ω Verification: X/R = 4/6 = 2/3, ℓx/ℓR = 40/60 =…
What is the principle of potentiometer? Define potential gradient.
Answer
Principle: Potential difference between two points on a uniform wire carrying steady current is directly proportional to the length between those points. Mathematically: VAC = K×ℓ, where K is potentia…
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