# Two metal wires of identical dimensions are connected in series. If $$\sigma_1~\text{and}~\sigma_2$$ 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 EMF $$E_{0 }$$ and resistance $$r_{1}$$. An unknown EMF is balanced at a length l of the potentiometer wire. The EMF $$E$$ 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. $$\frac{L E_{0} r}{\left(\right. r + r_{1} \left.\right) l}$$

Subtopic:  Meter Bridge & Potentiometer |
76%
From NCERT
NEET - 2015
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A potentiometer wire has a length of $$4​​~\text{m}$$ and resistance  $$8~\Omega.$$  The resistance that must be connected in series with the wire and an energy source of emf $$2~\text{V}$$, so as to get a potential gradient of $$1~\text{mV}$$ per cm on the wire is:
1. $$32~\Omega$$
2. $$40~\Omega$$
3. $$44~\Omega$$
4. $$48~\Omega$$

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 |
82%
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 $$2.0~\text{V}$$ and negligible internal resistance. The potentiometer wire itself is $$4~\text{m}$$ 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 $$3~\text{m}$$ and $$2.85~\text{m}$$, 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 |
65%
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 |
83%
From NCERT
AIPMT - 2013
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