An electric wire of length ‘I’ and area of cross-section a has a resistance R ohms. Another wire of the same material having the same length and area of cross-section 4a has a resistance of :

1. 4R

2. R/4

3. R/16

4. 16R

Subtopic:  Derivation of Ohm's Law |
 75%
From NCERT
PMT - 1993
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If \(n\), \(e\), \(\tau\) and \(m\) respectively represent the density, charge relaxation time and mass of the electron, then the resistance of a wire of length \(l\) and area of cross-section \(A\) will be:
1. \(\frac{ml}{ne^2\tau A}\)
2. \(\frac{m\tau^2A}{ne^2l}\)
3. \(\frac{ne^2\tau A}{2ml}\)
4. \(\frac{ne^2 A}{2m\tau l}\)

Subtopic:  Current & Current Density |
 79%
From NCERT
PMT - 1992
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The relaxation time in conductors :

1. Increases with the increase in temperature

2. Decreases with the increase in temperature

3. It does not depend on the temperature

4. All of the sudden changes at 400 K

Subtopic:  Current & Current Density |
 73%
From NCERT
PMT - 2003
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Which of the following has a negative temperature coefficient of resistance?

1. C

2. Fe

3. Mn

4. Ag

Subtopic:  Derivation of Ohm's Law |
 71%
From NCERT
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The reciprocal of resistance is :

1. Conductance

2. Resistivity

3. Voltage

4. None of the above

Subtopic:  Derivation of Ohm's Law |
 84%
From NCERT
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A solenoid is at the potential difference of \(60~\text V\) and the current flows through it is \(15~\text A\) then the resistance of the coil will be:
1. \(4~\Omega\)
2. \(8~\Omega\)
3. \(0.25~\Omega\)
4. \(2~\Omega\)

Subtopic:  Derivation of Ohm's Law |
 92%
From NCERT
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All of the following statements are true except 

1. Conductance is the reciprocal of resistance and is measured in Siemens

2. Ohm's law is not applicable at very low and very high temperatures

3. Ohm's law is applicable to semiconductors

4. Ohm's law is not applicable to electron tubes, discharge tubes and electrolytes

Subtopic:  Derivation of Ohm's Law |
 71%
From NCERT
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The resistance of a discharge tube is :

1. Ohmic

2. Non-ohmic

3. Both (1) and (2)

4. Zero

Subtopic:  Derivation of Ohm's Law |
 62%
PMT - 1999
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σ1 and σ2 are the electrical conductivities of Ge and Na respectively. If these substances are heated, then

1. Both σ1 and σ2 increase

2. σ1 increases and σ2 decreases

3. σ1 decreases and σ2 increases

4. Both σ1 and σ2 decrease

Subtopic:  Derivation of Ohm's Law |
 62%
From NCERT
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Masses of 3 wires of same metal are in the ratio 1 : 2 : 3 and their lengths are in the ratio 3 : 2 : 1. The electrical resistances are in ratio

1. 1 : 4 : 9

2. 9 : 4 : 1

3. 1 : 2 : 3

4. 27 : 6 : 1

Subtopic:  Derivation of Ohm's Law |
 67%
From NCERT
PMT - 2002
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