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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A solenoid is at the potential difference 60 V and current flows through it is 15 ampere, then the resistance of coil will be :

(1) 4 Ω

(2) 8 Ω

(3) 0.25 Ω

(4) 2 Ω

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 |
 72%
From NCERT
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