Electricity

41.Metals are good conductors of electricity because-
 
A. They have free electrons
 
B. Their atoms are lighter
 
C. They have high melting point
 
D. All of the above
 
Option “A” is correct.
Metals are good conductors of electricity because they have free electrons. These free electrons act as charge carriers in the metallic structure, allowing electric current to flow through them.
42.Which of the following is the best electrical conductor
 
A. Copper
 
B. Iron
 
C. Aluminum
 
D. Silver
 
Option “D” is correct.
Silver has an electrical conductivity of 6.30×107 S/m which is greatest for any known substance thus making it the best conductor of electricity.
43.A superconductor is characterized by__
 
A. High permeability
 
B. Low permeability
 
C. Zero permeability
 
D. Infinite permeability
 
Option “C” is correct.
Superconductors take the diamagnetic effect to the extreme, since in a superconductor the field B is zero – the field is completely screened from the interior of the material. Thus the relative permeability of a superconductor is zero.
44.Which of the following is not a semiconductor
 
A. Germanium
 
B. Silicon
 
C. Selenium
 
D. Krypton
 
Option “D” is correct.
Semiconductors are those elements which have less conductivity than a conductor but more conductivity than an insulator. Krypton is a member of the noble gases elements and thus it is not a semiconductor.
45.Substances which do not have free electrons in normal state but can be obtained under special conditions like high temperature or adding impurities are called
 
A. Conductive material
 
B. Non conductive material
 
C. Dielectric material
 
D. Semiconductor material
 
Option “D” is correct
46.What is the effect on the electrical resistance and electrical conductivity of conducting substances on increasing the temperature?
 
A. Electrical resistance increases while electrical conductivity decreases
 
B. Electrical resistance decreases while electrical conductivity increases
 
C. Both electrical resistance and electrical conductivity decrease
 
D. Both electrical resistance and electrical conductivity increase
 
Option “A” is correct.
If the temperature of a metal conductor increases, the ions of the metal vibrate more vigorously. This increases the number of collisions between the free electrons and the ions. Hence, for a metal, resistance increases with increasing temperature.
47.Copper is mainly used for conducting electricity because-
 
A. It has a higher melting point
 
B. It is cheaper
 
C. It is very durable
 
D. Its electrical resistivity is low
 
Option “D” is correct.
Copper is used for electrical wiring because it is a good conductor of electricity. The free electrons in metals can move through the metal, allowing metals to conduct electricity.
48.Which of the following is the unit of electronic current?
 
A. Kelvin
 
B. Values
 
C. Ohm
 
D. Ampere
 
Option”D” is correct
49.Electric current does not flow between two charged objects connected together if they are
 
A. On the same charge
 
B. At equal capacity
 
C. At equal resistance
 
D. At the same potential
 
Option “D” is correct.
There is no current flows between two charged bodies connected together when they have the same potential. For the flow of current between two conductors is that there must be a potential difference. Only then the electrons can flow from a higher potential to a lower potential.
50.The alternating current is converted into direct current by
 
A. Filter
 
B. Rectifier
 
C. Motor
 
D. Transformer
 
Option “B” is correct.
A rectifier converts alternating current to direct current and this process of converting AC to DC is known as rectification.

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