# 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%
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PMT - 2001
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σ1 and σ2 are the electrical conductivities of Ge and Na respectively. If these substances are heated, then

(1) Both σ1 and σ2 increase

(2) σ1 increases and σ2 decreases

(3) σ1 decreases and σ2 increases

(4) Both σ1 and σ2 decrease

Subtopic:  Derivation of Ohm's Law |
62%
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Masses of 3 wires of same metal are in the ratio 1 : 2 : 3 and their lengths are in the ratio 3 : 2 : 1. The electrical resistances are in ratio

(1) 1 : 4 : 9

(2) 9 : 4 : 1

(3) 1 : 2 : 3

(4) 27 : 6 : 1

Subtopic:  Derivation of Ohm's Law |
67%
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PMT - 2002
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A wire of radius r has resistance R. If it is stretched to a radius of $\frac{3r}{4}$, its resistance becomes

(1) $\frac{9R}{16}$

(2) $\frac{16R}{9}$

(3) $\frac{81R}{256}$

(4) $\frac{256R}{81}$

Subtopic:  Derivation of Ohm's Law |
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A copper wire has a square cross-section, 2.0 mm on a side. It carries a current of 8 A and the density of free electrons is 8 × 1028 m–3. The drift speed of electrons is equal to

(1) 0.156 × 10–3 m.s–1

(2) 0.156 × 10–2 m.s–1

(3) 3.12 × 10–3 m.s–1

(4) 3.12 × 10–2 m.s–1

Subtopic:  Current & Current Density |
60%
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What length of the wire of specific resistance $48×{10}^{-8}\text{\hspace{0.17em}}\Omega \text{\hspace{0.17em}\hspace{0.17em}}m$is needed to make the resistance of 4.2 Ω (diameter of wire = 0.4 mm

(1) 4.1 m

(2) 3.1 m

(3) 2.1 m

(4) 1.1 m

Subtopic:  Derivation of Ohm's Law |
64%
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PMT - 2000
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A strip of copper and another of germanium are cooled from room temperature to 80 K. The resistance of

(1) Each of these increases

(2) Each of these decreases

(3) Copper strip increases and that of germanium decreases

(4) Copper strip decreases and that of germanium increases

Subtopic:  Derivation of Ohm's Law |
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The length of a given cylindrical wire is increased by 100%. Due to the consequent decrease in diameter, the change in the resistance of the wire will be :

(1) 300%

(2) 200%

(3) 100%

(4) 50%

Subtopic:  Derivation of Ohm's Law |
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Express which of the following setups can be used to verify Ohm’s law

 (1) (2) (3) (4)
Subtopic:  Derivation of Ohm's Law |
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In a hydrogen discharge tube, it is observed that through a given cross-section 3.13 × 1015 electrons are moving from right to left and 3.12 × 1015 protons are moving from left to right per sec. What is the electric current in the discharge tube and what is its direction :

(1) 1 mA towards the right

(2) 1 mA towards left

(3) 2 mA towards left

(4) 2 mA towards the right

Subtopic:  Current & Current Density |
63%
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