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

Concept Questions :-

Derivation of Ohm's law
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A wire of radius r has resistance R. If it is stretched to a radius of 3r4, its resistance becomes 

(1) 9R16

(2) 16R9

(3) 81R256

(4) 256R81

Concept Questions :-

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

Concept Questions :-

Current and current density
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What length of the wire of specific resistance 48×108Ω  mis 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

Concept Questions :-

Derivation of Ohm's law
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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

Concept Questions :-

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%

Concept Questions :-

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)

Concept Questions :-

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. 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

Concept Questions :-

Current and current density
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A resistance R is stretched to four times its length. Its new resistance will be 

(1) 4 R

(2) 64 R

(3) R/4

(4) 16 R

Concept Questions :-

Derivation of Ohm's law
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What is the resistance of a carbon resistance which has bands of colours brown, black and brown 

(1) 100 Ω

(2) 1000 Ω

(3) 10 Ω

(4) 1 Ω

Concept Questions :-

Colour coding of resistors
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