Class 10 Science Chapter 11: Electricity worksheet with answer key
A 20-mark worksheet on Electricity for about 40 minutes of class or homework: 5 multiple-choice, 3 very short answer and 3 short answer questions, written from the NCERT chapter and checked by a second reviewer. Print the PDF for the class; the answer key carries the marking scheme. Teachers may photocopy it freely.
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Answer: (a) 4 C
Each electron carries 1.6 × 10⁻¹⁹ C, so Q = 2.5 × 10¹⁹ × 1.6 × 10⁻¹⁹ C = 4 C.
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Answer: (a) 0.2 A
I = V/R: with V unchanged, three times the resistance gives one-third the current, 0.6 A / 3 = 0.2 A.
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Answer: (b) a straight line through the origin
At constant temperature V is directly proportional to I for a metallic conductor, so the V-I graph is a straight line passing through the origin.
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Answer: (c) an ammeter and a voltmeter
An ammeter is always connected in series with the part whose current it measures; a voltmeter is always connected in parallel across the two points whose potential difference it measures.
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Answer: (a) 3.5 Ω
R ∝ l. The piece is 0.5 m / 2 m = 1/4 of the length, so R = 14 Ω / 4 = 3.5 Ω.
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Series: Rs = 3 + 6 = 9 Ω, P = V²/R = 36/9 = 4 W. Parallel: 1/Rp = 1/3 + 1/6 = 1/2, Rp = 2 Ω, P = 36/2 = 18 W. Ratio = 4 : 18 = 2 : 9.
- Rs = 9 Ω and Rp = 2 Ω (1)
- heat per second 4 W and 18 W, ratio 2 : 9 (1)
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The chemical action within the cell generates the potential difference across its terminals even when no current is drawn. When the bulb is connected, the potential difference sets charges in motion; to maintain this current the cell must keep expending its stored chemical energy, so it slowly runs down.
- chemical action produces the potential difference even with no current drawn (1)
- maintaining a current uses up the cell's stored chemical energy (1)
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Constantan's resistivity is 49/1.84 ≈ 27 times that of manganese, so a constantan wire of the same length and thickness has about 27 times the resistance (R = ρl/A). Her claim is wrong: manganese conducts better. The resistivity of an alloy is generally higher than that of its constituent metals.
- compares resistivities: constantan about 27 times manganese (1)
- concludes manganese conducts better; alloys generally have higher resistivity (1)
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(i) I = V/R = 230/46 = 5 A; P = VI = 230 × 5 = 1150 W. (ii) H = Pt, so t = 207000 J / 1150 W = 180 s = 3 minutes.
- I = V/R = 5 A (1)
- P = VI = 1150 W (1)
- t = H/P = 180 s (1)
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In parallel each appliance has the full 230 V across it, and I = P/V. Microwave 1150/230 = 5 A; mixer 460/230 = 2 A; light 69/230 = 0.3 A. The currents add: total 7.3 A. (ii) The toaster would draw 1000/230 ≈ 4.35 A, making the total about 11.65 A, more than 10 A: the fuse would melt. So no.
- each current from I = P/V at the full 230 V: 5 A, 2 A, 0.3 A (1)
- currents add: 7.3 A (1)
- toaster 4.35 A takes the total to 11.65 A, above 10 A, so the fuse melts (1)
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(i) Most of the power consumed by the filament appears as heat; only a small part is radiated as light, so the lamp and its glass get very hot. (ii) The supports keep the filament thermally isolated as far as possible, so it stays hot. (iii) Nitrogen and argon are chemically inactive, which prolongs the life of the filament.
- most of the filament's power becomes heat, little as light (1)
- insulating supports: thermal isolation of the filament (1)
- chemically inactive gases prolong the filament's life (1)
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