CURRENT ELECTRICITY PART-1 DPP

 

1.    The electric field E, current density J and conductivity of a conductor are related as:

a)    σ = E/J

b)    σ = J/E

c)    σ = JE

d)    σ = 1/JE     

2.    Two wires each of radius of cross-section r but of different materials are connected together end to end (in series). If the densities of charge carriers in the two wires are in the ratio 1:4, the drift velocity of electrons in the two wires will be in the ratio:

b)    1:2

c)    4:1

d)    2:1

e)    1:4    

3.    A current of 5 A is passing through a metallic wire of cross-sectional area 4 x 10^-6 m². If the density of charge carriers of the wire is 5 x 10²⁶ m^-3, then the drift velocity of the electrons will be:

1. 1 x 10² m/s
2. 1.56 x 10^-2 m/s
3. 1.56 x  10^-3 m/s
4. 1 x 10^-2 m/s   

4.    Drift velocity varies with the intensity of electric field as per the relation:

1. V_d ∝ E
2. V_d ∝ 1/E
3. V_d = constant
4. V_d ∝ E²     

 

5.    What is the effect of heating of a conductor on the drift velocity of free electrons?

1. Increases
2. Decreases
3. Remains constant
4. None of the above 

6.    What is the SI unit of mobility?
a) Vm-1
b) m²V-1s-1
c) mV-2
d) m2V-2s-1

7.    A steady current flows in a metallic conductor of non-uniform cross-section. Which of the following quantities is constant along the conductor?

1. Drift Speed
2. Current
3. Current Density
4. None of these

8.    Calculate the drift velocity of free electrons if a current of 5 A is maintained in a conductor of cross-section 10^-2m². The number density of free electrons is 5 × 10²⁰m^-3.
a) 6.25 ms^-1
b) 5.25 ms^-1
c) 2.25 ms^-1
d) 12.25 ms^-1     

 

9.    Predict the effect of temperature of the conductor on the drift velocity of electrons.
a) Drift velocity varies linearly with temperature
b) Drift velocity does not depend on the temperature
c) Drift velocity increases with increasing temperature
d) Drift velocity decreases with increasing temperature    

 

10. A potential difference of 100 V is applied across a conductor of length 50cm. Calculate the drift velocity of electrons if the electron mobility is 9 × 10^-5 m²V^-1s^-1.
a) 0.001 ms^-1
b) 1.800 ms^-1
c) 0.018 ms^-1
d) 0.180 ms^-1  

 

11.  Predict the effect of length of conductor on drift velocity of electrons.
a) Drift velocity varies linearly with the length of conductor
b) Drift velocity does not depend on the length of conductor
c) Drift velocity increases with the increasing length of conductor
d) Drift velocity decreases with the increasing length of conductor  

 

12.  Calculate the drift velocity of free electrons if a current of 200 A is maintained in a conductor of cross-section 10^-3m². The number density of free electrons is 96 × 10²⁰ m^-3.
a) 130.20 ms^-1
b) 13.020 ms^-1
c) 1.3020 ms^-1
d) 0.1302 ms^-1         

 

 

 

13. A wire of length 2m and another wire of length 5m are made up of the same material and have the same area of cross section, which wire has higher resistance?
a) Both have equal resistance
b) The 2m wire has higher resistance
c) The 5m wire has higher resistance
d) The value of resistance cannot be determined from the given data  

 

14. The resistance of a wireis 5Ω,its new resistance in ohm if stretched to 5times of its original lengthwill be

        (a)125                       (b)5                  (c)25             (d)625

15. In a conductor,If the no of free electrons per unit volume is 8.5x10²⁸ m^-3 and mean free time is 25fs its approximate resistivity is

        (a)10^-6Ωm                (b) 10^-7 Ωm          (c)10^-5 Ωm                 10^-8 Ωm                        

 

KEY

1.b  2.b  3.b 4.a 5.b 6.b 7.b 8.a 9.d 10.c 11.d  12.a 13.c 14.a 15.c