1BSEB 2025 · board paper · Q15 · page 81 mark
1 kilowatt-hour is equal to—
- (A) 100 unit
- (B) 10 unit
- (C) 1 unit
- (D) None of these
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Correct answer: (C) 1 unit
One unit on the electricity bill = 1 kWh = 3.6 × 10⁶ J (lesson 7).
Class 10 · Science · Chapter 11: Electricity
Class 10 Science Chapter 11: Important & Previous Year Questions – Bihar Board
Bihar Board · NCERT · CBSE
Only board questions that already carry a verified year are listed — BSEB annual exam questions (previous years) and questions from the board's official model set (marked separately, not an annual exam). No year is guessed. Answers are written by Study With Me, not an official answer key.
← Chapter 11: Electricity — full notes, video, questions
🏛️ BSEB 2025 · annual secondary exam (previous year questions)
2BSEB 2025 · board paper · Q16 · page 81 mark
The SI unit of electric power is—
- (A) Volt
- (B) Watt
- (C) Joule
- (D) Newton
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Correct answer: (B) Watt
Power P = VI is measured in watt (W) = 1 J/s (lesson 7).
3BSEB 2025 · board paper · Q19 · page 91 mark
On which principle of electric current does an electric fuse work?
- (A) Magnetic
- (B) Chemical
- (C) Thermal
- (D) None of these
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Correct answer: (C) Thermal
Too much current heats and melts the fuse wire — the thermal (heating) effect of current (lesson 8).
4BSEB 2025 · board paper · Q21 · page 91 mark
To increase the value of resistance, resistors should be connected in—
- (A) Series
- (B) Parallel
- (C) Both (A) and (B)
- (D) None of these
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Correct answer: (A) Series
In series R = R₁ + R₂ + R₃ — the total is larger than each one (lesson 5).
5BSEB 2025 · board paper · Q22 · page 101 mark
Which material is used for making the coil of an electric heater?
- (A) Iron
- (B) Silver
- (C) Nichrome
- (D) Copper
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Correct answer: (C) Nichrome
The alloy nichrome — high resistivity, and it does not oxidise (burn) even when red-hot (lessons 4, 7).
6BSEB 2025 · board paper · Q3 · page 272 marks
Write three important features of fuse wire.
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- High resistivity — even a little extra current produces a lot of heat.
- Low melting point — it melts quickly and breaks the circuit (an alloy of metals such as Al, Cu, Fe, Pb).
- The right thickness for a fixed rating (1 A, 2 A, 3 A, 5 A, 10 A); it is put in series in the live wire (lesson 8).
7BSEB 2025 · board paper · Q6 · page 272 marks
Why is series connection not used in domestic electrical circuits?
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- In series, when one appliance fails the circuit breaks and all stop; they cannot have separate switches.
- The total resistance rises, the current falls and the voltage is shared — no appliance gets the full 220 V.
- So houses use parallel connection (NCERT exercise 18c) (lessons 5, 6).
📄 BSEB model set 2026 (official board model paper, not an annual exam) — important
8BSEB model paper 2026 (not the annual exam) · Q16 · page 71 mark
On which effect of electric current does the electric fuse work?
- (A) Magnetic
- (B) Thermal
- (C) Chemical
- (D) None of these
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Correct answer: (B) Thermal
The fuse wire melts by the thermal (heating) effect (H = I²Rt) (lesson 8).
9BSEB model paper 2026 (not the annual exam) · Q17 · page 71 mark
Which instrument does not have positive (+) and negative (−) signs?
- (A) Ammeter
- (B) Voltmeter
- (C) Coil
- (D) Electric cell
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Correct answer: (C) Coil
An ammeter, a voltmeter and a cell have + and − terminals (to be connected the right way); a coil (resistance wire) does not (lesson 2).
10BSEB model paper 2026 (not the annual exam) · Q18 · page 81 mark
Which of the following units is equal to watt (W)?
- (A) J/s
- (B) J/s²
- (C) J⁻¹s⁻¹
- (D) J⁻²s⁻²
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Correct answer: (A) J/s
Power = energy ÷ time, so 1 W = 1 J/s (lesson 7).
11BSEB model paper 2026 (not the annual exam) · Q19 · page 81 mark
The coil of wire of an electric heater is made of—
- (A) Copper
- (B) Zinc
- (C) Tungsten
- (D) Nichrome
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Correct answer: (D) Nichrome
A heater coil is nichrome — high resistivity, and it does not burn when hot; tungsten is used in bulb filaments (lesson 7).
12BSEB model paper 2026 (not the annual exam) · Q4 · page 262 marks
Define the strength of electric current.
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Electric current (its strength) is the amount of charge flowing through a cross-section of a conductor per unit time.
I = Q / t
- SI unit ampere (A): 1 A = 1 C / 1 s. It is measured with an ammeter joined in series (lesson 1).
13BSEB model paper 2026 (not the annual exam) · Q5 · page 262 marks
On which factors does the heating effect of electric current depend?
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Joule's law of heating: H = I²Rt. The heat produced depends on —
- the square of the current (H ∝ I²)
- the resistance of the conductor (H ∝ R)
- the time the current flows (H ∝ t) (lesson 7).
14BSEB model paper 2026 (not the annual exam) · Q10 · page 276 marks
Obtain expressions for the equivalent resistance of resistors connected in series and resistors connected in parallel.
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(a) Series — R₁, R₂, R₃ one after another; the same current I in all; total voltage V = V₁ + V₂ + V₃.
- By Ohm's law V₁ = IR₁, V₂ = IR₂, V₃ = IR₃ and V = IRs
IRs = IR₁ + IR₂ + IR₃ ⇒ Rs = R₁ + R₂ + R₃
(b) Parallel — all three between two points; the same voltage V across each; total current I = I₁ + I₂ + I₃.
- I₁ = V/R₁, I₂ = V/R₂, I₃ = V/R₃ and I = V/Rp
V/Rp = V/R₁ + V/R₂ + V/R₃ ⇒ 1/Rp = 1/R₁ + 1/R₂ + 1/R₃
- (Diagram: both circuits — battery, key, ammeter in series, voltmeter in parallel.) In series Rs is more than the largest; in parallel Rp is less than the smallest (lessons 5, 6).