Tuesday, July 26, 2011

A Short MCQ from Current Electricity

1. Which of the following has negative temperature coefficient of resistance?
(a) Tungsten b) Carbon c) Nichrome d) Platinum
2. The length of a conductor is halved. Its conductance will be:
a) halved b) unchanged c) doubled d) quadrupled
3. A copper wire of length 1 metre and radius 1 mm is joined in series with an iron wire of length two metres and radius 3 mm and a current is passed through the wires. The ratio of the current density in the copper and iron wires is :
a) 18:1 b) 9:1 c) 6:1 d) 2:3
4. Carbon resistors used in electronic circuits are marked for their resistance value and tolerance by a
colour scheme. A given resistor has a colour scheme brown, black, green and gold. Its value is (in ohm):
a) 3.2 x 105 +/-5% b) 1.0 x 106 +/-10% c) 1.0 x 106 +/- 5% d) 1.0 x 103 +/-5%
5. Three resistances of 10 ohm, 5ohm, 2ohm respectively are connected in parallel. Net resistance will be:
a) more than 10 ohm b) between 10 ohm and 5 ohm c) between 5 ohm and 2 ohm d) less than 2 ohm
6. In a circuit containing two unequal resistors connected in parallel:
a) the current is same in both the resistors b) the current is larger in larger resistance c) the voltage drop is same across both the resistances d) the voltage drop is larger across larger resistance
7. A piece of Aluminium (Al) and Germanium (Ge) are cooled from T1 K to T2 K. The resistance of :
a) each of them increases b) each of them decreases c) Aluminium increases and that of Germanium decreases d) Aluminium decreases and that of Germanium increases
8. In the Bohr model of hydrogen atom the electron moves around the nucleus in a circular orbit of radius 5 x 10-11 metres. Its time period is 1.5 x 10-16 second. The current associated with the electron motion is:
a) zero b) 1.6 x 10-19A c) 0.17 A d) 1.07 x 10-3 A
9. Certain substances lose their electrical resistance at very low temperature. These substances are called:
a) good conductors b) semi – conductors c) super conductors d) dielectrics
10. A wire of length 5 m and radius 1 mm has a resistance 1 ohm. What length 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
11. A metal wire of specific Resistance 64 x 10-6 ohm. cm and length 198 cm has a resistance of 7 ohms, the radius of the wire will be:
a) 2.4 cm b) 0.24 cm c) 0.024 cm d) 24 cm
12. The resistance of a wire of iron is 10 ohm and temperature coefficient of resistivity is 5 x 10-3/ºC. At 20ºC it carries 30 milli ampere of current. Keeping constant potential difference between its ends, the temperature of the wire is raised to 120 ºC. The current in milli amperes that flows in the wire is:
a) 20 b) 15 c) 10 d) 40
13. At 0 K, Germanium behaves as a:
a) conductor b) insulator c) super conductor d) ferromagnetic substance
14. Which of the following is an ohmic conductor?
a) transistors b) thermionic valves c) constantan d) electrolyte
15. The cross sectional area of an aluminum square rod is 5 x 10-3 m2 and length is 1 m. If the resistivity of the aluminium is 2.8 x 10-8 ohm. m, its resistance will be:
a) 1.24 x 10-4 ohm b) 2.42 x 10-3 ohm  c) 0.56 x 10-5 ohm  d) 11.2 x 10-3 ohm

16. A wire has resistance 12 ohms. It is bent in the form of an equilateral triangle. The effective resistance between any two corners of the triangle is :
a) 9/4 ohms b) 12 ohms c) 6 ohms d) 8/3 ohms
17. The equivalent resistance of the parallel combination is:
a) smaller than the largest resistance b) larger than the largest resistance
c) smaller than the smallest resistance d) larger than the smallest resistance
18. The resistance of straight conductor does not depend upon its:
a) shape of cross-section b) temperature c) material d) length
19. Reciprocal of specific resistance is:
a) conductive resistance b) specific conductance c) conductive reactance d) plate resistance

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