CBSE PHYSICS

**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 meters 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 10

^{5}+/-5%
b) 1.0 x 10

^{6}+/-10%
c) 1.0 x 10

^{6}+/- 5%
d) 1.0 x 10

^{3}+/-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’s 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

^{-19}A
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 20 ºC 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}Ω. m, its resistance will be:
a) 1.24 x 10

^{-4}Ω
b) 2.42 x 10

^{-3}Ω
c) 0.56
x 10

^{-5}Ω
d) 11.2 x 10-3 Ω

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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