Numerical Problems of Current Electricity - Unit-2 Class - 12th Previous Exam Questions
Q.1 Current of 4.8 amperes is flowing through a conductor. The number of electrons per second will be
(a) 3 × 1019 (b) 7.68 × 1021 (c) 7.68 × 1020 (d) 3 × 1020
Q.2 Which one is not the correct statement
(a) 1 volt × 1 coulomb = 1 joule
(b) 1 volt × 1 ampere = 1 joule / second
(c) 1 volt × 1 watt = 1 H.P.
(d) watt-hour can be expressed in eV
Q.3 If a 0.1 % increase in length due to stretching, the percentage increase in its resistance will be
(a) 0.2 % (b) 2 % (c) 1 % (d) 0.1 %
Q.4 The specific resistance of manganin is 50 × 10-8 ohm × m. The resistance of a cube of length 50 cm will be
(a) 10-6 ohm (b) 2.5 × 10-6 ohm (c) 10-6 ohm (d) 5 × 10-4 ohm
Q.5 When the length and area of cross-section both are doubled, then its resistance
(a) Will become half (b) Will be doubled
(c) Will remain the same (d) Will become four times
Q.6 The resistance of a wire is 20 ohms. It is so stretched that the length becomes three times, then the new resistance of the wire will be
(a) 6.67 ohms (b) 60.0 ohms (c) 120 ohms (d) 180.0 ohms
Q.7 The resistivity of a wire
(a) Increases with the length of the wire (b) Decreases with the area of cross-section
(c) Decreases with the length and increases with the cross-section of wire
(d) None of the above statements are correct
Q.8 Ohm's law is true
(a) For metallic conductors at low temperature (b) For metallic conductors at high temperature
(c) For electrolytes when current passes through them (d) For diode when current flows
Q.9 The example for non-ohmic resistance is
(a) Copper wire (b) Carbon resistance (c) Diode (d) Tungston wire
Q.10 The temperature coefficient of resistance for a wire is 0.00125 / 0 C. At 300K its resistance is 1 ohm. The temperature at which the resistance becomes 2 ohm is
(a) 1154 K (b) 1100 K (c) 1400 K (d) 1127 K
Q.11 Drift velocity vd varies with the intensity of electric field as per the relation
(a) vd ∝ E (b) vd ∝ 1/E (c) vd = constant (d) vd ∝ E2
Q.12 On increasing the temperature of a conductor, its resistance increases because
(a) Relaxation time decreases (b) Mass of the electrons increases
(c) Electron density decreases (d) None of the above
Q.13 The specific resistance of a wire is ρ, its volume is 3 m3 and its resistance is 3 ohms, then its length will be
Q.14 A piece of wire of resistance 4 ohms is bent through 1800 at its mid point and the two halves are twisted together, then the resistance is
(a) 8 ohms (b) 1 ohm (c) 2 ohms (d) 5 ohms
Q.15 A wire 100 cm long and 2.0 mm diameter has a resistance of 0.7 ohm, the electrical resistivity of the material is
(a) 4.4 × 10-6 ohm × m (b) 2.2 × 10-6 ohm × m
(c) 1.1 × 10-6 ohm × m (d) 0.22 × 10-6 ohm × m
Q.16 A certain wire has a resistance R. The resistance of another wire identical with the first except having twice its diameter is
(a) 2 R (b) 0.25 R (c) 4 R (d) 0.5 R
Q.17 In hydrogen atom, the electron makes 6.6 × 1015 revolutions per second around the nucleus in an orbit of radius 0.5 × 10-10 . It is equivalent to a current nearly
(a) 1 A (b) 1 mA (c) 1 µA (d) 1.6 × 10-19
Q.18 A wire of length 5 m and radius 1 mm has a resistance of 1 ohm. What length of the wire of the same material at the same temperature and of radius 2 mm will also have a resistance of 1 ohm
(a) 1.25 m (b) 2.5 m (c) 10 m (d) 20 m
Q.19 When there is an electric current through a conducting wire along its length, then an electric field must exist
(a) Outside the wire but normal to it (b) Outside the wire but parallel to it
(c) Inside the wire but parallel to it (d) Inside the wire but normal to it
Q.20 Through a semiconductor, an electric current is due to drift of
(a) Free electrons (b) Free electrons and holes
(c) Positive and negative ions (d) Protons
Q.21 The specific resistance of all metals is most affected by
(a) Temperature (b) Pressure (c) Degree of illumination (d) Applied magnetic field
Q.22 The positive temperature coefficient of resistance is for
(a) Carbon (b) Germanium (c) Copper (d) An electrolyte
Q.23 Dimensions of a block are 1 cm × 1 cm × 100 cm. If specific resistance of its material is 3 × 10-7 ohm × m , then the resistance between the opposite rectangular faces is
(a) 3 × 10-9 ohm (b) 3 × 10-7 ohm (c) 3 × 10-5 ohm (d) 3 × 10-3 ohm
Q.24 Dimensions of a block are 1 cm × 1 cm × 100 cm. If specific resistance of its material is 3 × 10-7 ohm × m , then the resistance between the opposite square faces is
(a) 3 × 10-9 ohm (b) 3 × 10-7 ohm (c) 3 × 10-5 ohm (d) 3 × 10-3 ohm
Q.25 There is a current of 20 amperes in a copper wire of 10-6 square metre area of cross-section. If the number of free electrons per cubic metre is 1029 , then the drift velocity is
(a) 125 × 10-3 m/sec (b) 12.5 × 10-3 m/sec (c) 1.25 × 10-3 m/sec (d) 1.25 × 10-4 m/sec
Q.27 The relaxation time in conductors
(a) Increases with the increase of temperature
(b) Decreases with the increase of temperature
(c) It does not depend on temperature
(d) All of sudden changes at 400 K
Q.28 Resistance of tungsten wire at 1500 C is 133 ohm. Its resistance temperature coefficient is 0.0045 / 0 C. The resistance of this wire at 5000 C will be
(a) 180 ohm (b) 225 ohm (c) 258 ohm (d) 317 ohm
Q.29 Which of the following has a negative temperature coefficient
(a) C (b) Fe (c) Mn (d) Ag
Q.30 A platinum resistance thermometer has a resistance of 50 ohm at 200 C . When dipped in a liquid the resistance becomes 76.8 ohm. The temperature coefficient of resistance for platinum is 3.92 × 10-3 / 0 C. The temperature of the liquid is
(a) 1000 C (b) 1370 C (c) 1670 C (d) 2000 C
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