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A set of ‘n’ equal resistors, of value ‘R’ each, are  connected in series to a battery of emf ‘E’ and internal resistance ‘R’. The current drawn is I. Now, the ‘n’ resistors are connected in parallel to the same battery. Then the current drawn from battery becomes 10 I. The value of ‘n’ is

(A)

20

(B)

11

(C)

10

(D)

9

NEET - Medical UG-2018 Medium

Answer & Solution:

\(\large E=emf\\ \text{~series combination of n equal resistor} \\ R_{eq}=nR\\R_{total}=(n+1)R\\ \Large {I_1}={E\over R_{total}}={E\over (n+1)R} \\ \text{ ~parallel combination of n equal resistor} \\ \Large {1\over R_eq}={n\over R} \\ \Large R_{eq}={R\over n} \\ \Large R_{total}={R\over n}+R={Rn\over (n+1)}\\ \Large {I_2}={E(n+1)\over Rn} \\It \text{ is given} \\I_2=10I_1 \\ \Large {E(n+1)\over Rn} =10×{E\over (n+1)R} \\n=10 \)

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Other Questions of the same topic

Q1:

A potentiometer wire has length 4 m and resistance 8\(\large \Omega \). The resistance that must be connected in series with the wire and an accumulator of e.m.f. 2V, so as to get a potential gradient 1 mV per cm on the wire is :

(A)

40\(\large \Omega \)

(B)

44 \(\large \Omega \)

(C)

48 \(\large \Omega \)

(D)

32\(\large \Omega \)

NEET - Medical UG-2015 Medium

Q2:

A metallic rod of mass per unit length 0·5 kg \(m^{-1}\) is lying horizontally on a smooth inclined plane which makes an angle of 30° with the horizontal. The rod is not allowed to slide down by flowing a current through it when a  magnetic field of induction 0·25 T is acting on it in the vertical direction. The current flowing in the rod to keep it stationary is

(A)

14.76 A

(B)

5.98 A

(C)

7.14 A

(D)

11.32 A

NEET - Medical UG-2018 Medium

Q3:

A long solenoid has 1000 turns. When a current of 4A flows through it, the magnetic flux linked with each turn of the solenoid is \(\large 4\times 10^{-3} \) Wb. The self-inductance of the solenoid is

(A)

1 H

(B)

4 H

(C)

3 H

(D)

2 H

NEET - Medical UG-2016 Medium

Q4:

A carbon resistor of (47 \(\pm\) 4·7) k\(\Omega\) is to be marked with rings of different colours for its identification. The colour code sequence will be

(A)

Yellow – Green – Violet – Gold

(B)

Yellow – Violet – Orange – Silver

(C)

Violet – Yellow – Orange – Silver

(D)

Green – Orange – Violet – Gold

NEET - Medical UG-2018 Medium

Q5:

Two cities are 150 km apart. Electric power is sent from one city to another city through copper wires. The fall of potential per km is 8 volt and the average resistance per km is 0.5 \(\large \Omega \) The power loss in the wire is:

(A)

19.2W

(B)

19.2kW

(C)

19.2J

(D)

12.2kW

NEET - Medical UG-2014 Medium

Chemistry Biology

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