Question 31 : The internal resistance of a cell of emf 12 V is 5 x 10 -2 Ω . It is connected across an unknown resistance. Voltage across the cell, when a current of 60 A is drawn from it, is
1. 15 V
2. 12 V
3. 6 V
4. 15 V
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Question 32 : Which of the following does not obey Ohm's law
1. Diode-valve
2. Copper
3. Aluminium
4. None of these
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Question 33 : Two resistance r1 and r2 (r1 < r2 ) are connected in parallel. Their equivalent resistance R is
1. r1 < R < ( r1 + r2)
2. R < r1
3. r1 < R < r2
4. R < ( r1 > r2)
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Question 34 : A uniform resistance wire of length L and diameter d has a resistance R. Another wire of same material has length 4L and diameter 2d, the resistance will be
1. R/2
2. 2R
3. R
4. R/4
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Question 35 : A wire of 50 cm long and 1 mm² in cross-sectional area carries a current 4A when connected to a 2V battery. The resistivity of the wire is
1. 4 x 10^-6 Ωm
2. 2 x 10^-7 Ωm
3. 5 x 10^-7 Ωm
4. 1 x 10^-6 Ωm
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Question 36 : Three resistors are connected to form the sides of a triangle ABC, the resistance of the sides AB, BC and CA are 40 ohms; 60 ohms and 100 ohms respectively. The effective resistance between the points A and B in ohms will be
1. 64
2. 200
3. 50
4. 32
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Question 37 : Read the following statements carefully Y: The resistivity of a semiconductor decreases with increase of temperature Z : In a conducting solid, rate of collisions between free electrons and ions increases with increases of temperature Select the correct statements (s) from the following
1. Both Y and Z are true
2. Y is false but Z is true
3. Y is true and Z is the correct reason for Y
4. Y is true but Z is false
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Question 38 : A uniform wire of resistance R is uniformly compressed along its length, until its radius becomes n times the original radius. New resistance of the wire becomes
1. nR
2. R/n²
3. R/n⁴
4. R/n
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Question 39 : Identify the set in which all the three materials are good conductor of electricity
1. Cu, Ag, Au
2. Cu, Ag, Au
3. Cu, Si, Diamond
4. Cu, Ge, Hg
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Question 40 : The resistance of an incandescent lamp is
1. Greater when switched off
2. The same whether it is switched off or switched on
3. Smaller when switched on
4. None of these
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