Two metal wires of identical dimensions are connected in series. If \(\sigma_1\) and \(\sigma_2\) are the conductivities of the metal wires respectively, the effective conductivity of the combination is:
1. \(\frac{2\sigma_1 \sigma_2}{\sigma_1+\sigma_2}\)
2. \(\frac{\sigma_1 +\sigma_2}{2\sigma_1\sigma_2}\)
3. \(\frac{\sigma_1 +\sigma_2}{\sigma_1\sigma_2}\)
4. \(\frac{\sigma_1 \sigma_2}{\sigma_1+\sigma_2}\)

Subtopic:  Derivation of Ohm's Law |
 63%
From NCERT
NEET - 2015
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A potentiometer wire of length L and a resistance r are connected in series with a battery of e.m.f. \(E_{0 }\)and resistance \(r_{1}\). An unknown e.m.f. is balanced at a length l of the potentiometer wire. The e.m.f. E will be given by:

1. \(\frac{L E_{0} r}{l r_{1}}\)

2. \(\frac{E_{0} r}{\left(\right. r + r_{1} \left.\right)} \cdot \frac{l}{L}\)

3. \(\frac{E_{0} l}{L}\)

4. \(\frac{L E_{0} r}{\left(\right. r + r_{1} \left.\right) 1}\)

Subtopic:  Meter Bridge & Potentiometer |
 77%
From NCERT
NEET - 2015
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A potentiometer wire has a length of 4 m and resistance  \(8~\Omega.\)  The resistance that must be connected in series with the wire and an energy source of emf 2 V, so as to get a potential gradient of 1 mV per cm on the wire is:

1. 32 Ω
2. 40 Ω
3. 44 Ω
4. 48 Ω

Subtopic:  Meter Bridge & Potentiometer |
 65%
From NCERT
NEET - 2015
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\(\mathrm{A, B}~\text{and}~\mathrm{C}\) are voltmeters of resistance \(R\), \(1.5R\) and \(3R\) respectively as shown in the figure above. When some potential difference is applied between \(\mathrm{X}\) and \(\mathrm{Y}\), the voltmeter readings are \({V}_\mathrm{A}\), \({V}_\mathrm{B}\) and \({V}_\mathrm{C}\) respectively. Then:

       

1. \({V}_\mathrm{A} ={V}_\mathrm{B}={V}_\mathrm{C}\)
2. \({V}_\mathrm{A} \neq{V}_\text{B}={V}_\mathrm{C}\)
3. \({V}_\mathrm{A} ={V}_\mathrm{B}\neq{V}_\mathrm{C}\)
4. \({V}_\mathrm{A} \ne{V}_\mathrm{B}\ne{V}_\mathrm{C}\)

Subtopic:  Kirchoff's Voltage Law |
 65%
From NCERT
NEET - 2015
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Across a metallic conductor of non-uniform cross-section, a constant potential difference is applied. The quantity which remains constant along the conductor is:
1. current density
2. current
3. drift velocity
4. electric field
Subtopic:  Current & Current Density |
 59%
From NCERT
NEET - 2015
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Two cities are \(150~\text{km}\) apart. Electric power is sent from one city to another city through copper wires. The fall of potential per km is \(8\) volts and the average resistance per km is \(0.5~\text{ohm}\). The power loss in the wire is:
1. \(19.2~\text{W}\)
2. \(19.2~\text{kW}\)
3. \(19.2~\text{J}\)
4. \(12.2~\text{kW}\)

Subtopic:  Heating Effects of Current |
 83%
From NCERT
AIPMT - 2014
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The figure given below shows a circuit when resistances in the two arms of the meter bridge are \(5~\Omega\) and \(R\), respectively. When the resistance \(R\) is shunted with equal resistance, the new balance point is at \(1.6l_1\). The resistance \(R\) is: 
           
1. \(10~\Omega\)
2. \(15~\Omega\)
3. \(20~\Omega\)
4. \(25~\Omega\)

Subtopic:  Meter Bridge & Potentiometer |
 73%
From NCERT
AIPMT - 2014
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A potentiometer circuit has been set up for finding the internal resistance of a given cell. The main battery, used across the potentiometer wire, has an emf of 2.0 V and negligible internal resistance. The potentiometer wire itself is 4 m long. When the resistance, R, connected across the given cell, has values of (i) infinity (ii) 9.5, the 'balancing lengths, on the potentiometer wire, are found to be 3 m and 2.85 m, respectively. The value of the internal resistance of the cell is (in ohm):

1. 0.25

2. 0.95

3. 0.5

4. 0.75

Subtopic:  Meter Bridge & Potentiometer |
 66%
From NCERT
AIPMT - 2014
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A wire of resistance \(4~\Omega\) is stretched to twice its original length. The resistance of a stretched wire would be:
1. \(4~\Omega\)
2. \(8~\Omega\)
3. \(16~\Omega\)
4. \(2~\Omega\)

Subtopic:  Derivation of Ohm's Law |
 82%
From NCERT
AIPMT - 2013
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Internal resistance of a \(2.1~\text{V}\) cell which gives a current of \(0.2~\text{A}\) through a resistance of \(10~\Omega\) is:
1. \(0.5~\Omega\)
2. \(0.8~\Omega\)
3. \(1.0~\Omega\)
4. \(0.2~\Omega\)
Subtopic:  EMF & Terminal Voltage |
 85%
From NCERT
AIPMT - 2013
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