Electricity | Most Probable Exam ready objective Questions ( MCQs) : 1 Mark

1. In case of four wires of same material, the resistance will be minimum if the diameter and length of the wire respectively are:
(a) $\frac{\mathrm{D}}{2}$ and $\frac{\mathrm{L}}{4}$
(b) $\frac{\mathrm{D}}{4}$ and 4 L
(c) 2D and L
(d) 4 D and 2 L
[CBSE 2024]

Answer: (d) 4 D and 2 L

2. In the given circuit the total resistance between X and Y is:

(a) $12 \Omega$
(b) $4 \Omega$
(c) $6 \Omega$
(d) $1 \Omega$
[CBSE 2024]

Answer: (d) $1 \Omega$

3. The values of mA and $\mu \mathrm{A}$ are:
(a) $10^{-6}$ and $10^{-9} \mathrm{~A}$ respectively
(b) $10^{-3}$ and $10^{-6} \mathrm{~A}$ respectively
(c) $10^{-3}$ and $10^{-9}$ A respectively
(d) $10^{-6}$ and $10^{-3} \mathrm{~A}$ respectively
[CBSE 2020]

Ans. (b) $10^{-3} \mathrm{~A}$ and $10^{-6} \mathrm{~A}$ respectively

4. The resistance of a resistor is reduced to half of its initial value. In doing so, if other parameters of the circuit remain unchanged, the heating effects in the resistor will become:
(a) two times
(b) half
(c) one-fourth
(d) four times
[CBSE 2020]

Ans. (a) two times

5. (a) At the time of short circuit, the electric current in the circuit:
(a) vary continuously
(b) does not change
(c) reduces substantially
(d) increases heavily
[CBSE 2020]

Answer : (d) increases heavily

6. Two bulbs of $100 \Omega$ and $40 \Omega$ are connected in series. The current through the $100 \Omega$ bulb is 1 A . The current through the $40 \Omega$ bulb will be:
(a) 0.4 A
(b) 0.6 A
(c) 0.8 A
(d) 1 A
[CBSE 2020]
Answer : (d) 1 A

7. When a 4 V battery is connected across an unknown resistor there is a current of 100 mA in the circuit. The value of the resistance of the resistor is:
(a) $4 \Omega$
(b) $40 \Omega$
(c) $400 \Omega$
(d) $0.4 \Omega$
[CBSE 2019]
Answer : (b) $40 \Omega$

8. When we connect too many electrical appliances to a single socket in a circuit having a fixed value of current rating:
(a) the total resistance of the circuit increases.
(b) the current drawn from the source decreases.
(c) the current increases beyond the rated value.
(d) each appliance starts drawing more and more current from the source.
[CBSE Compartment 2024]

Ans. (c) the current increases beyond the rated value.

9. The image shows a combination of 4 resistors.

What is the net resistance between the two points in the circuit?
(a) $0.5 \Omega$
(b) $1.0 \Omega$
(c) $1.5 \Omega$
(d) $2.0 \Omega$
[CBSE Question Bank 2022]

Answer : (b) $1.0 \Omega$

10. The maximum resistance which can be made using four resistors each of resistance $\frac{1}{2} \Omega$ is:
(a) $2 \Omega$
(b) $1 \Omega$
(c) $2.5 \Omega$
(d) $8 \Omega$
[CBSE 2020]

Answer : (a) $2 \Omega$

11.If four identical resistors, of resistance 8 ohm, are first connected in series so as to give an effective resistance $R_2$, and then connected in parallel so as to give an effective resistance $R_p$, then the ratio $\frac{R_s}{R_p}$ is:
(a) 32
(b) 2
(c) 0.5
(d) 16
[CBSE 2023]

Answer : (d) 16

12. Plastic insulation surrounds a wire having diameter $d$ and length $l$ as shown below. A decrease in the resistance of the wire would be produced by an increase in the:

(a) length $l$ of the wire
(b) diameter $d$ of the wire
(c) temperature of the wire
(d) thickness of the plastic insulation
[CBSE SQP 2022]
Ans. (b) diameter $d$ of the wire

13. The same resistors are connected in a parallel combination in the circuit.

What is the equivalent resistance of the circuit?
(a) Less than $1 \Omega$
(b) $1 \Omega$
(c) $2 \Omega$
(d) More than $2 \Omega$
[CBSE Question Bank 2022]
Ans. (a) Less than $1 \Omega$

14. The picture shows an electric circuit.

Which of these is true about the circuit?
(I) The circuit is open.
(II) The circuit has double batteries.
(III) The circuit has an ammeter and a voltmeter parallel to each other.
Options:
(a) Only (I)
(b) Only (II)
(c) Only (III)
(d) (I) and (III)
[CBSE Question Bank 2022]
Ans. (b) Only (II)

15. A wire of length ‘ $l$ ‘ is gradually stretched so that its length increases to 3$l$ . If its original resistance is $R$, then its new resistance will be :

(a) $3 R$
(b) 6 R
(c) $9 R$
(d) 27 R
Answer: (c) $9 R$

16. 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 $\mathrm{R}^{\prime}$, then the value of $R / \mathrm{R}^{\prime}$ is:
[Delhi 2025]
(a) $1 / 9$
(b) $1 / 3$
(c) 3
(d) 9
Answer: (d) 9

17. The minimum number of identical bulb of rating $4 \mathrm{~V} ; 6 \mathrm{~W}$, that can work safely with desired brightness, when connected in series with a 240 V mains supply is:
[Delhi 2025]
(a) 20
(b) 40
(c) 60
(d) 80

Answer: (c) 60

18. An electric bulb is rated $220 \mathrm{~V} ; 11 \mathrm{~W}$. The resistance of its filament when it glows with a power supply of 220 V is:
[Delhi 2025]
(a) $4400 \Omega$
(b) $440 \Omega$
(c) $400 \Omega$
(d) $20 \Omega$

Answer: (a) $4400 \Omega$

19. Assertion (A): One circuit with 15 A current rating is used for appliances such as geysers and air coolers.

Reason (R): Appliances with metallic body are connected to an earth wire with low resistance.

Answer these questions selecting the appropriate option given below:

(a) Both (A) and (R) are true, and (R) is the correct explanation of (A).

(b) Both (A) and (R) are true, and (R) is not the correct explanation of (A).

(c) (A) is true but (R) is false.

(d) (A) is false but (R) is true.

Ans. (b) Both (A) and (R) are true, and (R) is not the correct explanation of (A).

Explanation: The assertion that one circuit with a 15 A current rating is used for appliances like geysers and air coolers is valid based on the anticipated power requirements of these devices. However, the reason provided, stating that appliances with metallic bodies are connected to an earth wire with low resistance, does not directly explain the specific choice of a 15 A current rating for the circuit. The connection to an earth wire is generally a safety measure to dissipate fault currents, but it doesn’t inherently determine the precise current rating chosen for the circuit.

20. Assertion(A): Electric appliances with metallic body have three pin connection, whereas an electric bulb has a two pin connection.

Reason (R): Three pin connection reduces heating of connecting wires.

[DIKSHA]

Answer these questions selecting the appropriate option given below:

(a) Both (A) and (R) are true, and (R) is the correct explanation of (A).

(b) Both (A) and (R) are true, and (R) is not the correct explanation of (A).

(c) (A) is true but (R) is false.

(d) (A) is false but (R) is true.

Ans. (c) (A) is true but (R) is false.

Explanation: The three pin connection of electric appliances with metallic body are live wire, neutral wire and earth wire. The live and neutral wire supply electric current to the appliance, whereas the earth wire, which is connected to the metal body of the electric appliance, protects us from electric shock in case we touch the metal body of appliances. In case of an electric shock, the current passes directly to the earth through the earth wire and we do not feel the electric shock. On the contrary, three-pin connection do not reduce heating of connecting wires. Also, we hardly touch electric bulb with hands, so three pin connection is not required. The earth wire connection is not present in a bulb

21. Assertion (A): Alloys are commonly used in electrical heating devices like electric iron and heater.

Reason (R): Resistivity of an alloy is generally higher than that of its constituent metals but the alloys have low melting points than their constituent metals.

[CBSE 2020]

Answer these questions selecting the appropriate option given below:

(a) Both (A) and (R) are true, and (R) is the correct explanation of (A).

(b) Both (A) and (R) are true, and (R) is not the correct explanation of (A).

(c) (A) is true but (R) is false.

(d) (A) is false but (R) is true.

Ans. (a) Both ( $A$ ) and ( $R$ ) are true, and ( $R$ ) is the correct explanation of (A).

Explanation: Alloys have more resistivity than that of its constituent elements because alloys have better properties than that of metals. Resistivity is the property of material that explains how strongly the material opposes flow of electrons. Higher the resistivity, smaller will be the conductivity i.e., why alloys are used in electrical heating devices.

Related Theory

– Metals have higher melting point as the atoms are arranged in a regular manner and form a strong bond whereas alloys are made up of different metals. The different sizes of atoms in an alloy make their arrangement less regular than a pure metal. This makes the bonds between the atoms weakened and lowers the melting point.

22. Assertion (A): The commercial unit of electric energy is kilowatt hour (kWh).

Reason (R): $\quad 1 \mathrm{kWh}=10^6$ joule (J)

[CBSE Compartment 2024]

Answer these questions selecting the appropriate option given below:

(a) Both (A) and (R) are true, and (R) is the correct explanation of (A).

(b) Both (A) and (R) are true, and (R) is not the correct explanation of (A).

(c) (A) is true but (R) is false.

(d) (A) is false but (R) is true.

Ans. (c) (A) is true but (R) is false.

Explanation: The energy consumed in the circuit at the rate of 1 kilowatt for 1 hour.

And. $\quad 1 \mathrm{kWh}=\left(1 \times 10^3\right)(1$ hour $)$

We know that,

$$

1 \text { watt }=1 \mathrm{Js}^{-1}

$$

So,

$$

\begin{aligned}

1 \mathrm{kWh} & =\left(1000 \mathrm{Js}^{-1}\right)(1 \times 60 \times 60 \mathrm{~s}) \\

& =3.6 \times 10^6 \mathrm{~J}

\end{aligned}

$$

23. Assertion (A): At high temperatures, metal wires have a greater chance of short circuiting.

Reason (R): Both resistance and resistivity of a material vary with temperature.

[CBSE 2020]

Answer these questions selecting the appropriate option given below:

(a) Both (A) and (R) are true, and (R) is the correct explanation of (A).

(b) Both (A) and (R) are true, and (R) is not the correct explanation of (A).

(c) (A) is true but (R) is false.

(d) (A) is false but (R) is true.

Ans. (b) Both (A) and (R) are true, and (R) is not the correct explanation of (A).

Explanation: At high temperatures, the free electrons start moving at a greater speed and more heat is evolved. The increased amount of heat melts the insulation of wires and wires have greater chance of short circuiting. Sometimes the short circuit may even melt the wire and it may cause fire. Both resistance and resistivity vary with temperature. When the temperature is increased, the random motion of electrons increases. As a result, the number of collision increases between atoms and electrons.