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 7 of 19

1. Q121 CBSE 2026
   1. (i)​Name the ​device which (I) helps to change the electric current in the given electric circuit and (II) breaks the circuit during short-circuiting.
   2. (ii)State Ohm’s law and write the factors on which the resistance of a ​given conductor depends.
   3. (iii)Find ​out the ​length of a wire of resistance $21\Omega$, if ​the diameter of the wire is $0.02$ cm and ​resistivity of the material is $66\times 10^{-8}\Omega \text{m}$. ​[Given : $\pi =\frac{22}{7}$]
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   A rheostat and a fuse are the devices, resistance depends on four factors, and the wire is $1$ m long.

   (i) (I) A rheostat (a variable resistance), which changes the resistance and hence the current in the circuit. (II) An electric fuse (or a miniature circuit breaker), whose wire melts when the large short-circuit current flows and so breaks the circuit. (ii) Ohm's law: the potential difference across the ends of a metallic conductor is directly proportional to the current flowing through it, provided its temperature remains the same; $V=IR$. The resistance of a conductor depends on its length ($R\propto l$), its area of cross-section ($R\propto \frac{1}{A}$), the nature of its material (its resistivity $\rho$) and its temperature, so that $R=\rho \frac{l}{A}$. (iii) $r=\frac{0.02}{2}$ cm $=1\times 10^{-4}$ m, $A=\pi r^2=\frac{22}{7}\times 10^{-8}$ m${}^2$, and $l=\frac{RA}{\rho }=\frac{21\times \frac{22}{7}\times 10^{-8}}{66\times 10^{-8}}=1$ m.

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2. Q122 CBSE 2025
   In case of wires of same ​resistivity, the resistance of ​the wire will ​be maximum if the ​diameter and ​length of ​the wire respectively ​are

   1. (a)$D$ and $L$
   2. (b)$\frac{D}{2}$ and $\frac{L}{4}$
   3. (c)$\frac{D}{3}$ and $\frac{L}{6}$
   4. (d)$\frac{D}{4}$ and $\frac{L}{12}$
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   (c) $\frac{D}{3}$ and $\frac{L}{6}$

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3. Q123 CBSE 2025
   A piece of wire of ​resistance ​‘$R$’ is cut lengthwise into three ​identical ​parts. ​These parts are then connected in parallel. If ​the equivalent resistance of this combination is $R^{\prime }$, then ​the value ​of $R/R^{\prime }$ is :

   1. (a)$1/9$
   2. (b)$1/3$
   3. (c)$3$
   4. (d)$9$
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   (d) $9$

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4. Q124 CBSE 2025
   A ​wire of length '$l$' is gradually stretched ​so that its length increases ​to $3l$. ​If its ​original resistance is $R$, then its ​new ​resistance will be :

   1. (a)$3R$
   2. (b)$6R$
   3. (c)$9R$
   4. (d)$27R$
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   (c) $9R$

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5. Q125 CBSE 2025
   Which ​one of ​the ​following ​factors affects the ​electrical resistivity ​of ​a conductor ?

   1. (a)Temperature
   2. (b)Length
   3. (c)Shape
   4. (d)Thickness
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   (a) Temperature

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6. Q126 CBSE 2025
   An electric bulb ​is rated $220$ ​V; $11$ ​W. The resistance of ​its ​filament when it glows ​with a power supply of $220$ V is :

   1. (a)$4400\Omega$
   2. (b)$440\Omega$
   3. (c)$400\Omega$
   4. (d)$20\Omega$
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   (a) $4400\Omega$

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7. Q127 CBSE 2025
   An electric ​bulb ​is ​connected to a power supply of $220$ V. ​If the ​current ​drawn by the ​bulb from the supply is $500$ mA, the power of the bulb ​is :

   1. (a)$11$ W
   2. (b)$110$ W
   3. (c)$220$ W
   4. (d)$1100$ W
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   (b) $110$ W

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8. Q128 CBSE 2025
   The minimum ​number of identical bulbs ​of ​rating 4V; 6W, ​that can work safely with desired brightness, when ​connected ​in series with a 240 V mains supply is :

   1. (a)20
   2. (b)40
   3. (c)60
   4. (d)80
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   (c) 60

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9. Q129 CBSE 2025
   The resistivity of a ​wire ​made ​of ​an alloy is ​generally ​:

   1. (a)Lower than that of its constituent metals.
   2. (b)Higher than that of its constituent metals.
   3. (c)Decreases with increase in its area of cross-section.
   4. (d)Increases with increase in its length.
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   (b) Higher than that of its constituent metals.

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10. Q130 CBSE 2025
    Four identical resistors of $12\Omega$ ​each are connected in ​series to form a square ABCD as ​shown ​in ​the figure. The resistance of ​the network between the two ​points $1$ ​and $2$ is :

    1. (a)$48\Omega$
    2. (b)$36\Omega$
    3. (c)$9\Omega$
    4. (d)$6\Omega$
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    (c) $9\Omega$

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11. Q131 CBSE 2025
    Four wires a, b, c and d ​are made of the same materials. ​If $l$ denotes length and $r$ denotes radius, then the wire which ​offers least resistance to the flow of ​electric ​current has length and radius ​respectively ​as :

    1. (a)$2l$ and $4r$
    2. (b)$l$ and $2r$
    3. (c)$4l$ and $\frac{r}{4}$
    4. (d)$\frac{l}{4}$ and $\frac{r}{2}$
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    (a) $2l$ and $4r$

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12. Q132 CBSE 2025
    The ​resistance ​of a ​wire is $40\Omega$. If $2$ A ​of current flows ​through this wire for $50$ seconds, the heat produced ​in ​the ​wire is

    1. (a)$4000$ J
    2. (b)$8000$ J
    3. (c)$16000$ J
    4. (d)$80000$ J
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    (b) $8000$ J

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13. Q133 CBSE 2025
    Two statements are given — one labelled as Assertion (A) and ​the other ​labelled as ​Reason ​(R). Select ​the correct ​answer from ​the codes given below.

    Assertion (A): Nichrome is an alloy which is commonly used in electrical heating devices such as electric irons, toasters, etc.

    Reason (R): The resistivity of nichrome is high and its resistance decreases with increase in temperature.

    1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
    2. (b)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
    3. (c)Assertion (A) is true, but Reason (R) is false.
    4. (d)Assertion (A) is false, but Reason (R) is true.
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    (c) Assertion (A) is true, but Reason (R) is false.

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14. Q134 CBSE 2025
    Two statements are given — one labelled as Assertion ​(A) and the other ​labelled as Reason ​(R). Select the correct answer ​to this question from the ​codes (a), (b), (c) and (d) as ​given below.

    Assertion (A): The bending of a wire in the form of a coil of several turns does not affect its electrical resistance.

    Reason (R): The electrical resistance of a wire is directly proportional to its electrical resistivity.

    1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
    2. (b)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
    3. (c)Assertion (A) is true, but Reason (R) is false.
    4. (d)Assertion (A) is false, but Reason (R) is true.
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    (b) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).

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15. Q135 CBSE 2025
    Consider the following circuits : In which circuit will ​the power dissipated in the circuit be ​(I) minimum ​(II) maximum ? ​Justify ​your ​answer.

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    Power is minimum (14.4 W) in circuit (ii) and maximum (57.6 W) in circuit (iii), because $P=\frac{V^2}{R}$ at the same voltage.

    (I) The power dissipated is minimum in circuit (ii), the two $5\Omega$ resistors in series: $R=10\Omega$ and $P=\frac{V^2}{R}=\frac{12^2}{10}=14.4$ W. (II) It is maximum in circuit (iii), the two $5\Omega$ resistors in parallel: $R=2.5\Omega$ and $P=\frac{12^2}{2.5}=57.6$ W. Justification: the same $12$ V is applied to each circuit, so $P=V^2/R$ is inversely proportional to the total resistance; circuit (i), with $R=5\Omega$, dissipates $28.8$ W, between the two.

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16. Q136 CBSE 2025
    Consider two ​lamps A ​and B of rating ​50 W; 220 V and ​25 W; 220 V respectively. Find the ratio ​of the resistances of the ​two lamps (i.e. $R_{\text{A}}:R_{\text{B}}$).
    Show answer

    The resistances of lamps A and B are in the ratio $R_A:R_B=1:2$.

    $R=\frac{V^2}{P}$, so $R_{\text{A}}=\frac{220^2}{50}=968\Omega$ and $R_{\text{B}}=\frac{220^2}{25}=1936\Omega$. Hence $R_{\text{A}}:R_{\text{B}}=968:1936=1:2$; the 25 W lamp has twice the resistance of the 50 W lamp.

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17. Q137 CBSE 2025
    Use ​Ohm’s law to ​determine the ​potential difference across the $6\Omega$ ​resistor in the following ​circuit when key is ​closed :

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    The potential difference across the $6\Omega$ resistor is 3 V.

    The three resistors are in series, so $R_s=2+6+4=12\Omega$ and the current is $I=\frac{V}{R_s}=\frac{6\text{V}}{12\Omega }=0.5$ A. By Ohm's law, the potential difference across the $6\Omega$ resistor is $V=IR=0.5\text{A}\times 6\Omega =3$ V.

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18. Q138 CBSE 2025
    Determine the ​maximum and ​minimum resistance which can be obtained ​by ​joining ​five resistors of $\frac{1}{5}\Omega$ each.
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    Maximum resistance is $1\Omega$ (all five in series); minimum is $0.04\Omega$ (all five in parallel).

    Maximum resistance: all five resistors in series, $R_{\text{max}}=5\times \frac{1}{5}\Omega =1\Omega$. Minimum resistance: all five resistors in parallel, $\frac{1}{R_{\text{min}}}=5+5+5+5+5=25{\Omega }^{-1}$, so $R_{\text{min}}=\frac{1}{25}\Omega =0.04\Omega$.

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19. Q139 CBSE 2025
    Two ​lamps, rated 100 W; 220 V and 60 ​W; 220 V are connected ​in parallel to electric main supply ​of 220 ​V. Find the current drawn ​by the two lamps ​from the supply.
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    The two lamps draw $I=\frac{8}{11}\text{A}\approx 0.73\text{A}$ from the supply.

    The current drawn from the supply is $I=I_1+I_2=\frac{100}{220}+\frac{60}{220}=\frac{160}{220}=\frac{8}{11}$ A $\approx 0.73$ A. Each lamp is connected across the full $220$ V, so it draws its rated current, $\frac{5}{11}$ A $\approx 0.45$ A for the $100$ W lamp and $\frac{3}{11}$ A $\approx 0.27$ A for the $60$ W lamp, and in parallel the currents add.

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20. Q140 CBSE 2025
    Heat produced per second due to ​a current in a ​resistor of $4\Omega$ ​is 400 joules. ​Calculate the ​potential difference across ​the resistor.
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    The potential difference across the resistor is 40 V.

    Heat produced per second is the power: $P=400$ W. From $H=I^{2}Rt$, $400=I^2\times 4\times 1$, so $I=10$ A, and $V=IR=10\times 4=40$ V. The potential difference across the resistor is $40$ V.

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