# 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 |
74%
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$$\sqrt{T}$$ 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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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, 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) $\frac{ml}{n{e}^{2}\tau A}$

(2) $\frac{m{\tau }^{2}A}{n{e}^{2}l}$

(3) $\frac{n{e}^{2}\tau A}{2ml}$

(4) $\frac{n{e}^{2}A}{2m\tau l}$

Subtopic:  Current & Current Density |
78%
From NCERT
PMT - 1992
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