# If a metallic block has no potential difference applied across it, then the mean velocity of free electron is: ($$T$$= absolute temperature of the block) 1. proportional to $$T$$. 2. proportional to$$\sqrt{T}$$ 3. zero. 4. finite but independent of temperature.

Subtopic:  Current & Current Density |
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The specific resistance of all metals is most affected by :

(1) Temperature

(2) Pressure

(3) Degree of illumination

(4) Applied magnetic field

Subtopic:  Derivation of Ohm's Law |
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The positive temperature coefficient of resistance is for :

(1) Carbon

(2) Germanium

(3) Copper

(4) An electrolyte

Subtopic:  Current & Current Density |
67%
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The electric intensity E, current density j and specific resistance k are related to each other by the relation :

(1) E = j/k

(2) E = jk

(3) E = k/j

(4) k = jE

Subtopic:  Current & Current Density |
67%
From NCERT
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The resistance of a wire of uniform diameter d and length L is R. The resistance of another wire of the same material but diameter 2d and length 4L will be :

(1) 2R

(2) R

(3) R/2

(4) R/4

Subtopic:  Derivation of Ohm's Law |
74%
From NCERT
PMT - 1984
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There is a current of 1.344 amp in a copper wire whose area of cross-section normal to the length of the wire is 1 mm2. If the number of free electrons per cm3 is 8.4 × 1022, then the drift velocity would be :

1. 1.0 mm/sec

2. 1.0 m/sec

3. 0.1 mm/sec

4. 0.01 mm/sec

Subtopic:  Current & Current Density |
57%
From NCERT
PMT - 1990
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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 |
78%
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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Resistance of tungsten wire at 150°C is 133 Ω. Its resistance temperature coefficient is 0.0045/°C. The resistance of this wire at 500°C will be

(1) 180 Ω

(2) 225 Ω

(3) 258 Ω

(4) 317 Ω

Subtopic:  Derivation of Ohm's Law |
From NCERT
PMT - 2004
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