# 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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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%
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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 |
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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%
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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 |
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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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A steady current flows in a metallic conductor of non-uniform cross-section. The quantity/ quantities constant along the length of the conductor is/are :

(1) Current, electric field and drift speed

(2) Drift speed only

(3) Current and drift speed

(4) Current only

Subtopic:  Current & Current Density |
58%
From NCERT
PMT - 2001
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