The positive temperature coefficient of resistance is for :

(1) Carbon

(2) Germanium

(3) Copper

(4) An electrolyte

Subtopic:  Current & Current Density |
 67%
From NCERT
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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 |
 75%
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 |
 76%
From NCERT
PMT - 1993
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If n, e, τ 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) mlne2τA

(2) mτ2Ane2l

(3) ne2τA2ml

(4) ne2A2mτl 

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 |
 74%
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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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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