Super conductivity can be destroyed by_____________?
(A) adding impurities
(B) reducing temperatures
(C) application of magnetic field
(D) any of the above
Which of the following affect greatly the resistivity of electrical conductors ?
(A) Composition
(B) Pressure
(C) Size
(D) Temperature
Most of the common metals have _________ structure?
(A) linear
(B) hexagonal
(C) orthorhombic
(D) cubic
Due to which of the following factors the brush wear rate is altered ?
(A) Speed of the machine
(B) Contact pressure
(C) Surface conditions of brush and commutator
(D) Excessive sparking
(D) All of the above
The impurity atoms is semiconductors_____________?
(A) inject more charge carriers
(B) reduce the energy gap
(C) increase the kinetic energy of valence electrons
(D) all of the above
Carbon resistors are used extensively because they are____________?
(A) easy to make
(B) compact
(C) inexpensive
(D) all of the above reasons
Which of the following are non-conductors of electricity?
(A) Non-metal solids except carbon
(B) Air and most other gases
(C) Pure water and liquids in general except mercury
(D) All of the above
Carbon rods are used in wet and dry cells because_____________?
(A) carbon rod serves as conductor
(B) carbon can resist the attack of battery acid
(C) both (A) and (B)
(D) either (A) or (B)
Which of the following material is not a semiconductor ?
(A) Silica
(B) Germanium
(C) Selenium
(D) Gallium-arsenide