The resistivity of a wire :

1. Increases with the length of the wire
2. Decreases with the area of cross-section
3. Decreases with the length and increases with the cross-section of the wire
4. None of the above statement is correct

Subtopic:  Derivation of Ohm's Law |
 73%
From NCERT
PMT - 1984
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Drift velocity vd varies with the intensity of electric field as per the relation: 

1. vdE

2. vd1E

3. vd = constant

4. vdE2 

Subtopic:  Current & Current Density |
 78%
From NCERT
PMT - 1981
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In a conductor 4 coulombs of charge flows for 2 seconds. The value of electric current will be :

(1) 4 volts

(2) 4 amperes

(3) 2 amperes

(4) 2 volts

Subtopic:  Current & Current Density |
 90%
From NCERT
PMT - 1984
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The specific resistance of a wire is ρ, its volume is 3 m3 and its resistance is 3 ohms, then its length will be 

(1) 1ρ

(2) 3ρ

(3) 1ρ3

(4) ρ13 

Subtopic:  Derivation of Ohm's Law |
 80%
From NCERT
PMT - 1984
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When a piece of aluminum wire of finite length is drawn through a series of dies to reduce its diameter to half its original value, its resistance will become :

(1) Two times

(2) Four times

(3) Eight times

(4) Sixteen times

Subtopic:  Derivation of Ohm's Law |
From NCERT
AIIMS - 2002
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Through a semiconductor, an electric current is due to drift off:

(1) Free electrons

(2) Free electrons and holes

(3) Positive and negative ions

(4) Protons

Subtopic:  Current & Current Density |
 75%
From NCERT
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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\(\sqrt{\mathrm{T}} \)
3. zero. 4. finite but independent of temperature.
Subtopic:  Current & Current Density |
 52%
From NCERT
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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 |
 88%
From NCERT
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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%
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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