In an electrical cable, there is a single wire of radius 9 mm of copper. Its resistance is 5 Ω. The cable is replaced by 6 different insulated copper wires, the radius of each wire is 3 mm. Now the total resistance of the cable will be :

(1) 7.5 Ω

(2) 45 Ω

(3) 90 Ω

(4) 270 Ω

Subtopic:  Combination of Resistors |
 51%
From NCERT
PMT - 1988
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Two uniform wires A and B are of the same metal and have equal masses. The radius of wire A is twice that of wire B. The total resistance of A and B when connected in parallel is :

(1) 4 Ω when the resistance of wire A is 4.25 Ω

(2) 5 Ω when the resistance of wire A is 4.25 Ω

(3) 4 Ω when the resistance of wire B is 4.25 Ω

(4) 7 Ω when the resistance of wire B is 4.25 Ω

Subtopic:  Combination of Resistors |
 59%
From NCERT
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Twelve wires of equal length and same cross-section are connected in the form of a cube. If the resistance of each of the wires is R, then the effective resistance between the two diagonal ends would be 

(1) 2R

(2) 12R

(3) 56R 

(4) 8R

Subtopic:  Combination of Resistors |
 85%
From NCERT
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You are given several identical resistances each of value R = 10 Ω and each capable of carrying maximum current of 1 ampere. It is required to make a suitable combination of these resistances to produce a resistance of 5 Ω which can carry a current of 4 amperes. The minimum number of resistances of the type R that will be required for this job 

(1) 4

(2) 10

(3) 8

(4) 20

Subtopic:  Combination of Resistors |
 64%
From NCERT
PMT - 1990
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The resistance of a wire is 10–6 Ω per metre. It is bend in the form of a circle of diameter 2 m. A wire of the same material is connected across its diameter. The total resistance across its diameter AB will be

(1) 43π×106Ω

(2) 23π×106Ω

(3) 0.88×106Ω

(4) 14π×106Ω

Subtopic:  Combination of Resistors |
 63%
From NCERT
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In the figure shown, the capacity of the condenser C is 2μF. The current in 2 Ω resistor is : 

(1) 9 A

(2) 0.9 A

(3) 19A

(4) 10.9A

Subtopic:  Combination of Resistors |
 78%
From NCERT
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When the key K is pressed at time t = 0, which of the following statements about the current I in the resistor AB of the given circuit is true?

(1) I = 2 mA at all t

(2) I oscillate between 1 mA and 2mA

(3) I = 1 mA at all t

(4) At t = 0 , I = 2 mA and with time it goes to 1 mA

Subtopic:  Kirchoff's Voltage Law |
 65%
PMT - 1995
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There are three resistance coils of equal resistance. The maximum number of resistances you can obtain by connecting them in any manner you choose, being free to use any number of the coils in any way is :

(1) 3

(2) 4

(3) 6

(4) 5

Subtopic:  Combination of Resistors |
From NCERT
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If in the circuit shown below, the internal resistance of the battery is 1.5 Ω and VP and VQ are the potentials at P and Q respectively, what is the potential difference between the points P and Q 

(1) Zero

(2) 4 volts (VP > VQ)

(3) 4 volts (VQ > VP)

(4) 2.5 volts (VQ > VP)

Subtopic:  Kirchoff's Voltage Law |
 58%
From NCERT
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Two wires of resistance R1 and R2 have temperature coefficient of resistance α1 and α2, respectively. These are joined in series. The effective temperature coefficient of resistance is :

(1) α1+α22

(2) α1α2

(3) α1R1+α2R2R1+R2

(4) R1R2α1α2R12+R22

Subtopic:  Combination of Resistors |
 74%
From NCERT
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