Bihar Board Class 10 · Science · Matric exam 2027
Chapter 12: Electricity — notes
The chapter’s 7 parts in the book’s order — the first idea of each and the points Medha Ma’am writes on the board — and the summary at the end. The full lesson and a check question for each part are in the app.
1. Electric Current and Circuit
Okay, so think about air current, or water current.
- • Electric circuit = continuous, closed path of current
- • I = Q/t
- • SI unit of current: ampere (A); 1 A = 1 C/1 s
- • 1 mA = 10^-3 A, 1 μA = 10^-6 A
- • Example: I = 0.5 A, t = 600 s, Q = It = 300 C
2. Electric Potential and Potential Difference
Okay, so think of water in a perfectly flat tube.
- • Potential difference V = Work done (W) / Charge (Q)
- • SI unit: volt (V); 1 V = 1 J/1 C
- • Voltmeter: connected in parallel
- • Example: V = 12 V, Q = 2 C
- • W = VQ = 12 × 2 = 24 J
3. Ohm's Law
Okay, so let's talk about Ohm's law.
- • Ohm's law: V ∝ I (temperature constant)
- • V = IR, so R = V/I
- • SI unit of resistance: ohm (Ω)
- • 1 ohm = 1 volt / 1 ampere
- • I = V/R
- • Example: V = 220 V, R = 1200 Ω, I = 0.18 A
4. Factors Affecting Resistance and Resistivity
Okay, so let's think about wires in a circuit.
- • R depends on: length, area of cross-section, material
- • R ∝ l, R ∝ 1/A
- • R = ρ l/A
- • ρ = resistivity, SI unit: Ω m
- • Metals: 10^-8 to 10^-6 Ω m (good conductors)
- • Insulators: 10^12 to 10^17 Ω m
5. Resistors in Series and Parallel
Okay, so — let's look at resistors in series first.
- • Series: I same everywhere; V = V1+V2+V3
- • Rs = R1 + R2 + R3
- • Parallel: V same across each; I = I1+I2+I3
- • 1/Rp = 1/R1 + 1/R2 + 1/R3
- • Example: R1 = 5,R2 = 10,R3 = 30 Ω, V = 12V
- • I1 = 2.4A, I2 = 1.2A, I3 = 0.4A, I total = 4A, Rp = 3 Ω
6. Heating Effect of Electric Current
Okay, so — a battery keeps current flowing by giving energy to the charges.
- • H = VIt
- • Joule's law: H = I^2 R t
- • Heat ∝ I^2, ∝ R, ∝ t
- • Example: H = 100J, R = 4Ω, t = 1s
- • I = √(H/Rt) = 5 A
- • V = IR = 5×4 = 20 V
7. Electric Power
Okay, so let's talk about electric power.
- • P = VI
- • P = I^2R = V^2/R
- • SI unit: watt (W); 1 W = 1 V × 1 A
- • 1 kW = 1000 W
- • 1 kWh = 3.6 × 10^6 J
- • Example: V = 220V, I = 0.50A, P = 110 W
Summary
You learned that electric current is the rate of flow of charge, I = Q/t, measured in amperes, and flows in a closed electric circuit. You saw that potential difference, V = W/Q, measured in volts, is what drives charges to flow, created by a battery and measured by a voltmeter. Then came Ohm's law, V = IR, which gave us resistance, measured in ohms. You learned that resistance depends on length, area of cross-section and material of the conductor, through R = ρl/A. You then saw how resistors combine in series, where current stays the same and resistances add up, and in parallel, where potential difference stays the same and reciprocals of resistance add up. Finally, you learned the heating effect of current, H = I2Rt, used in heaters and fuses, and electric power, P = VI, measured in watts, with kilowatt hour as the commercial unit of energy.
AskMedha · Medha Ma’am — Bihar Board Class 10 Science, Chapter 12. Written from the textbook, checked twice.
Questions parents and students ask
- How do I get the "Electricity" notes as a PDF?
- Press "Save as PDF" — the phone’s print sheet opens; choose "Save as PDF" there. The PDF holds the notes only.
- Where are these notes written from?
- From the chapter’s own textbook text, part by part, in the book’s own terms; a second, independent model then checked every part against the book. The full lesson, a check question for each part and the practice are in the AskMedha app.
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