Ecosystem

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

6. 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

7. (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

8. (2) 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

9. 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) $40 \Omega$

12. 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.

13. 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) $1.0 \Omega$

17. 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) $2 \Omega$

18.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

21. 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

22. 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 $1 \Omega$

24. 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)

98. 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) $9 R$