Class 10 Science · Chapter 11

Electricity

363 Class 10 Science questions on Electricity from the NCERT textbook, NCERT Exemplar and CBSE board papers 2018–2026, each with its answer and a step-by-step solution.

CBSE Class 10 Science previous year papers, with answers →

Questions · page 9 of 19

1. Q161 CBSE 2025
   The resistance ​of ​a wire of $0.01$ cm radius is $7$ ohms. ​If ​the ​resistivity ​of the ​material of the ​wire is $44\times 10^{-6}$ ohm meter, calculate the length of the wire.
   Show answer

   The length of the wire is $5\times 10^{-3}$ m, that is 0.005 m.

   $l=\frac{RA}{\rho }=\frac{7\times \frac{22}{7}\times 10^{-8}}{44\times 10^{-6}}=5\times 10^{-3}$ m, that is $0.005$ m ($5$ mm or $0.5$ cm).

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2. Q162 CBSE 2025
   Resistance ​of a wire of length $1$ m is $35\Omega$ at $20^{\circ }$C. If the diameter ​of the wire ​is $0.2$ mm, ​determine the resistivity of the material ​of the ​wire at that temperature. How will the resistivity of the wire change if the length and diameter of ​the wire both are doubled ​? Justify your answer. (Given that $\pi =\frac{22}{7}$)
   Show answer

   $\rho =1.1\times 10^{-6}\Omega$ m, and it does not change when the length and diameter are both doubled.

   Resistivity $\rho =\frac{RA}{l}=\frac{35\times \frac{22}{7}\times 10^{-8}}{1}=1.1\times 10^{-6}\Omega$ m. If the length and the diameter of the wire are both doubled, the resistivity does not change: it depends on the material of the wire and its temperature, not on its length or thickness. The resistance does change: the length doubles and the area becomes four times as large, so the resistance halves to $17.5\Omega$, and $\rho =RA/l$ gives the same value as before.

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3. Q163 CBSE 2025
   Define the ​term “potential difference” between two points ​in an electric circuit carrying ​current. Name and ​define ​its S.I. unit. ​Also express it in terms ​of S.I. unit of work and charge.
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   Potential difference is the work done per unit charge, $V=\frac{W}{Q}$; its SI unit is the volt, and $1\text{V}=1{\text{J C}}^{-1}$.

   Potential difference between two points in an electric circuit carrying current is the work done to move a unit charge from one point to the other: $V=\frac{W}{Q}$. Its SI unit is the volt (V): one volt is the potential difference between two points in a current-carrying conductor when $1$ joule of work is done to move a charge of $1$ coulomb from one point to the other. In terms of the SI units of work and charge, $1\text{V}=\frac{1\text{J}}{1\text{C}}=1{\text{J C}}^{-1}$.

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4. Q164 CBSE 2025
   1. (a)Write the relationship between resistivity and resistance of ​a cylindrical conductor of ​length $l$ ​and ​area of ​cross-section $A$. Hence derive the SI unit of resistivity.
   2. (b)​Why are alloys used in electrical ​heating ​devices ?
   Show answer

   Resistivity is $\rho =\frac{RA}{l}$ with SI unit ohm metre; alloys are used for heating because of high resistivity and resistance to oxidation.

   (a) For a cylindrical conductor of length $l$ and area of cross-section $A$, $R=\rho \frac{l}{A}$, so the resistivity is $\rho =\frac{RA}{l}$. Substituting the SI units, unit of $\rho =\frac{\Omega \times {\text{m}}^2}{\text{m}}=\Omega \text{m}$, so the SI unit of resistivity is the ohm metre ($\Omega \text{m}$). (b) Alloys are used in electrical heating devices because the resistivity of an alloy is much higher than that of its constituent pure metals, so a wire of practical size has a large resistance and produces a large amount of heat ($H=I^{2}Rt$); and alloys such as nichrome do not oxidise or burn readily even at high temperatures, so the heating element lasts long.

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5. Q165 CBSE 2025
   1. (a)Explain the ​statement "Potential ​difference between ​two points is 1 volt".
   2. (b)What ​do ​the symbols given below represent ​in an electric ​circuit ? Write one function of each.

   Show answer

   1 volt means 1 joule of work per coulomb; the symbols are an ammeter (measures current) and a rheostat (varies current).

   (a) The potential difference between two points is 1 volt when 1 joule of work is done in moving a charge of 1 coulomb from one point to the other; that is, $V=W/Q$ and $1\text{V}=1\text{J}{\text{C}}^{-1}$. (b) (i) An ammeter. It is connected in series in the circuit and measures the electric current flowing through it, its plus terminal being joined towards the positive terminal of the cell. (ii) A variable resistance, that is a rheostat. It is connected in series and is used to change the resistance of the circuit and so to vary the current flowing in it.

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6. Q166 CBSE 2025
   (a) Define Electric power. Express electric power of an electric appliance in terms of its resistance (R) and the voltage / potential difference (V) at which it ​operates. (b) ​The rated voltage of an air-conditioner is 220 V. ​This air-conditioner consumes 22 units of electric ​energy in 10 hours, calculate :

   1. (i)Power rating of the ​air-conditioner,
   2. (ii)Current ​drawn by the ​air-conditioner, and
   3. (iii)Resistance of the air-conditioner
   Show answer

   Power is the rate of consuming electric energy, $P=\frac{V^2}{R}$; the air-conditioner is 2200 W, draws 10 A and has resistance $22\Omega$.

   (a) Electric power is the rate at which electric energy is consumed or dissipated in a circuit, $P=\frac{W}{t}=VI$, measured in watts. Putting $I=\frac{V}{R}$ from Ohm's law gives $P=\frac{V^2}{R}$. (b)(i) $P=\frac{E}{t}=\frac{22\text{kWh}}{10\text{h}}=2.2$ kW $=2200$ W. (ii) $I=\frac{P}{V}=\frac{2200}{220}=10$ A. (iii) $R=\frac{V}{I}=\frac{220}{10}=22\Omega$, which agrees with $R=\frac{V^2}{P}=\frac{48400}{2200}=22\Omega$.

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7. Q167 CBSE 2025
   1. (i)If $R_s$ and $R_p$ respectively are the total ​resistances of the series and parallel combinations of ​the three ​resistors of resistances $R_1$, $R_2$ and $R_3$, then write the relationships among (I) $R_s$, $R_1$, $R_2$ and $R_3$ and (II) $R_p$, $R_1$, $R_2$ and $R_3$.
   2. (ii)An electric oven operates on ​the mains voltage of 220 V. This oven consumes $2.2$ kWh of electrical energy in one ​hour. Calculate : (I) power ​rating of the oven, (II) current drawn ​by the oven, and (III) resistance of the oven when in operation.
   Show answer

   Series: $R_s=R_1+R_2+R_3$, parallel: reciprocals add; the oven is $2200$ W, draws $10$ A and has resistance $22\Omega$.

   (i)(I) For the series combination: $R_s=R_1+R_2+R_3$. (II) For the parallel combination: $\frac{1}{R_p}=\frac{1}{R_1}+\frac{1}{R_2}+\frac{1}{R_3}$. (ii)(I) Power rating $P=\frac{E}{t}=\frac{2.2\text{kWh}}{1\text{h}}=2.2$ kW $=2200$ W. (II) Current drawn $I=\frac{P}{V}=\frac{2200}{220}=10$ A. (III) Resistance in operation $R=\frac{V}{I}=\frac{220}{10}=22\Omega$.

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8. Q168 CBSE 2025
   1. (i)Define the term electric power. Express it in terms of potential difference (V) and resistance ​(R).
   2. (ii)The ​resistance of a metal wire of length 6 m is $120\Omega$. If the area of cross-section of the wire is $4\times 10^{-7}{\text{m}}^2$, calculate the electrical resistivity of the material ​of the wire. How ​would the ​resistivity be affected if this wire is ​gradually stretched so that its length is doubled ​? ​Justify your answer.
   Show answer

   Power is $P=\frac{V^2}{R}$; the resistivity is $8\times 10^{-6}\Omega \text{m}$ and does not change when the wire is stretched.

   (i) Electric power is the rate at which electric energy is consumed or dissipated in a circuit, that is, the electrical work done per unit time; its SI unit is the watt. Since $P=VI$ and, by Ohm's law, $I=\frac{V}{R}$, the power in terms of the potential difference and the resistance is $P=\frac{V^2}{R}$. (ii) Using $R=\rho \frac{l}{A}$, the resistivity is $\rho =\frac{RA}{l}=\frac{120\times 4\times 10^{-7}}{6}=8\times 10^{-6}\Omega \text{m}$. If the wire is stretched so that its length is doubled, the resistivity is **not** affected — it remains $8\times 10^{-6}\Omega \text{m}$. Justification: resistivity is a characteristic property of the **material** of the wire; it depends only on the nature of the material and on its temperature, and not on the length, the area of cross-section or the shape of the specimen. Stretching changes only the geometry of this particular piece of wire, not the metal it is made of. What does change is the resistance: since the volume of metal is unchanged, doubling the length halves the area of cross-section, so $R^{\prime }=\rho \frac{2l}{A/2}=4R=480\Omega$.

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9. Q169 CBSE 2025
   As shown in the ​diagram, an electric circuit consisting of an ammeter, a voltmeter, 4 cells of $1.5$ V each, a plug key with a ​gap XY was set up. Voltmeter ​and ammeter readings were recorded in the observation table for ​four ​arrangements as given below: Arrangement No. 1 - only resistor $R_1$ in gap XY Arrangement No. 2 - only resistor $R_2$ in gap XY Arrangement No. 3 - Resistors $R_1$ and $R_2$ in series in gap XY Arrangement No. 4 - Resistors $R_1$ and $R_2$ in parallel in gap XY Based on the observations, four $V$-$I$ ​graphs A, B, C and D ​as shown in figure were drawn. Study these graphs.

   1. (a)Which one of the graphs represents the series combination of $R_1$ and $R_2$?[1]
   2. (b)Which one of these graphs represents the parallel combination of $R_1$ and $R_2$?[1]
   3. (c)(i)Show an arrangement of three resistors, each of resistance $10\Omega$, so that the combination has a resistance of $15\Omega$. Give justification for your answer.[2]
   4. (c)(ii)OR : A battery of $6$ V is connected with a series combination of five resistors of $0.1\Omega$, $0.2\Omega$, $0.3\Omega$, $0.4\Omega$ and $0.5\Omega$. How much current would flow through the $0.3\Omega$ resistor? Justify your answer.[2]
   Show answer

   Graph A is series and D is parallel; two $10\Omega$ in parallel plus one in series give $15\Omega$; or the current is 4 A.

   (a) Graph A represents the series combination of $R_1$ and $R_2$. On these axes the slope of a line is $I/V=1/R$, and the series resistance $R_1+R_2$ is the largest of the four, so it gives the least steep line. (b) Graph D represents the parallel combination, whose resistance $R_1{R}_2/(R_1+R_2)$ is the smallest of the four and so gives the steepest line. (c)(i) Connect two of the $10\Omega$ resistors in parallel and the third in series with that pair. The parallel pair gives $1/R_p=1/10+1/10=2/10$, so $R_p=5\Omega$, and the whole combination is $5+10=15\Omega$. (c)(ii) The five resistors are in series, so the total resistance is $0.1+0.2+0.3+0.4+0.5=1.5\Omega$ and the current drawn is $I=V/R=6/1.5=4$ A. The same current flows through every resistor of a series circuit, so the current through the $0.3\Omega$ resistor is $4$ A.

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10. Q170 CBSE 2025
    In ​a domestic circuit, six LED bulbs and ​a ceiling fan are arranged ​as ​per ​the circuit shown in the figure. The source voltage is 220 volts ​and the power rating of each device is marked ​in the circuit diagram. Two ​fuses ${\text{F}}_1$ and ${\text{F}}_2$ are also provided in the circuit. Based on the circuit diagram, answer the following questions :

    1. (a)State what happens when (i) only key ${\text{K}}_1$ is closed, (ii) and key ${\text{K}}_2$ is also closed.[1]
    2. (b)Find the current drawn by the bulb L.[1]
    3. (c)(i)Calculate the resistance of the bulb A. Find the total resistance offered by the circuit to the flow of current when only key ${\text{K}}_2$ is closed.[2]
    4. (c)(ii)OR : What would happen to the glow of the bulbs in the circuit when ${\text{K}}_1$ and ${\text{K}}_2$ both are closed and the fuse ${\text{F}}_1$ melts suddenly ? Give reason to justify your answer.[2]
    Show answer

    With ${\text{K}}_1$ only the fan and L work; ${\text{K}}_2$ adds A to E; $I_L\approx 0.09$ A, $R_A=193.6\Omega$, total $968\Omega$.

    (a)(i) With only ${\text{K}}_1$ closed, only the branch holding fuse ${\text{F}}_1$, the ceiling fan and bulb L is complete, so the fan runs and bulb L glows, both at their rated 220 V and therefore normally; bulbs A to E do not glow, their branch being open at ${\text{K}}_2$. The current drawn is $(40+20)/220=0.27$ A. (ii) When ${\text{K}}_2$ is closed as well, the series string A, B, C, D, E is completed and all five bulbs glow, each receiving $220/5=44$ V, exactly its rated voltage; the fan and bulb L are unaffected, because the branches are in parallel and each still has the whole 220 V across it, and the total current rises to $110/220=0.5$ A. (b) $I_L=P/V=20/220=1/11\approx 0.09$ A. (c)(i) $R_A=V^2/P=(44{)}^2/10=1936/10=193.6\Omega$. With only ${\text{K}}_2$ closed the only conducting path is the series string of the five bulbs, so the total resistance offered by the circuit is $R=5\times 193.6=968\Omega$. (c)(ii) The ceiling fan stops and bulb L goes out, because ${\text{F}}_1$ is in series with that branch alone and melting it breaks the branch. The five bulbs A, B, C, D and E continue to glow with exactly the same brightness as before, because they lie in a separate parallel branch that is still connected to the supply through ${\text{F}}_2$ and ${\text{K}}_2$: the potential difference across that branch is still 220 V, so the current in it is still $220/968=0.23$ A and each bulb still has 44 V across it and consumes 10 W.

    Step-by-step solution →
11. Q171 CBSE 2025
    Study ​the circuit shown in ​which two resistors X ​and ​Y of resistances $3\Omega$ and $6\Omega$ ​respectively are joined ​in ​series with ​a battery of $2$ V.

    1. (I)Draw a circuit diagram showing the above two resistors X and Y joined in parallel with same battery and same ammeter and voltmeter.[1]
    2. (II)In which combination of resistors will the (i) potential difference across X and Y and (ii) current through X and Y, be the same ?[1]
    3. (III)(a)Find the current drawn from the battery by the series combination of the two resistors (X and Y).[2]
    4. (III)(b)OR : Determine the equivalent resistance of the parallel combination of the two resistors (X and Y).[2]
    Show answer

    Parallel gives equal potential difference and series gives equal current; the series current is $0.22$ A, or the parallel resistance is $2\Omega$.

    (I) X and Y are drawn as two separate branches between the same pair of junctions, with the $2$ V battery and the plug key in the main circuit, the ammeter still in the main line and the voltmeter connected across the parallel pair (see the circuit diagram). (II) (i) The potential difference across X and Y is the same in the parallel combination; (ii) the current through X and Y is the same in the series combination. (III)(a) $R_s=3+6=9\Omega$, so the current drawn is $I=\frac{2}{9}\approx 0.22$ A. (III)(b) $\frac{1}{R_p}=\frac{1}{3}+\frac{1}{6}=\frac{1}{2}$, so $R_p=2\Omega$.

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12. Q172 CBSE 2024
    Two resistors ​of $1\Omega$ and $3\Omega$ ​are connected in parallel in a ​circuit. If ​a current of $1$ ampere is ​flowing through the ​circuit, the current flowing through ​the $3\Omega$ resistor is :

    1. (a)$1.0$ ampere
    2. (b)$0.75$ ampere
    3. (c)$0.33$ ampere
    4. (d)$0.25$ ampere
    Show answer

    (d) $0.25$ ampere

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13. Q173 CBSE 2024
    Two wires of same metal ​have the ​same ​length but their ​cross-sectional ​areas are in the ratio of $4:1$. ​They are joined in series. The ​resistance of the thicker wire is $20\Omega$. The total resistance of the combination is :

    1. (a)$25\Omega$
    2. (b)$100\Omega$
    3. (c)$16\Omega$
    4. (d)$340\Omega$
    Show answer

    (b) $100\Omega$

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14. Q174 CBSE 2024
    Consider ​the following combinations of resistors : The ​combinations ​having ​equivalent resistance $1\Omega$ ​is/are ​:

    1. (a)I and IV
    2. (b)Only IV
    3. (c)I and II
    4. (d)I, II and III
    Show answer

    (c) I and II

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15. Q175 CBSE 2024
    The maximum ​resistance of ​a ​network of ​five identical ​resistors of $\frac{1}{5}\Omega$ each ​can ​be ​–

    1. (a)$1\Omega$
    2. (b)$0.5\Omega$
    3. (c)$0.25\Omega$
    4. (d)$0.1\Omega$
    Show answer

    (a) $1\Omega$

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16. Q176 CBSE 2024
    S.I. ​unit ​of electrical ​resistivity ​is

    1. (a)ohm per metre${}^3$
    2. (b)ohm per metre${}^2$
    3. (c)ohm . metre
    4. (d)ohm . metre${}^3$
    Show answer

    (c) ohm . metre

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17. Q177 CBSE 2024
    In ​case of four wires of same material, the ​resistance will be ​minimum ​if the diameter ​and length of ​the wire respectively are

    1. (a)$D/2$ and $L/4$
    2. (b)$D/4$ and $4L$
    3. (c)$2D$ and $L$
    4. (d)$4D$ and $2L$
    Show answer

    (d) $4D$ and $2L$

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18. Q178 CBSE 2024
    In ​the ​given circuit ​the ​total resistance between X and Y is ​:

    1. (a)$12\Omega$
    2. (b)$4\Omega$
    3. (c)$6\Omega$
    4. (d)$1\Omega$
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    (d) $1\Omega$

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19. Q179 CBSE 2024
    An electric iron of resistance $20\Omega$ ​draws a ​current of $5$ ​A. The heat ​developed ​in ​the iron ​in $30$ seconds is :

    1. (a)15000 J
    2. (b)6000 J
    3. (c)1500 J
    4. (d)3000 J
    Show answer

    (a) 15000 J

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20. Q180 CBSE 2024
    You have ​four resistance ​wires of same material. Select the wire ​which will offer the ​least resistance to the ​flow of current in an ​electric circuit ​:

    1. (a)Length $2l$ and diameter $2d$
    2. (b)Length $l$ and diameter $d$
    3. (c)Length $l/2$ and diameter $d/2$
    4. (d)Length $l/4$ and diameter $d/4$
    Show answer

    (a) Length $2l$ and diameter $2d$

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