Wednesday, April 24, 2019

WBCS Polity and Constitution MCQs Prelims and Mains

WBCS Online Preparation of General Science (Physics) MCQs P14

131. In a p-type semiconductor, which is the main carrier of electricity?
(A) Electrons
(B) Negative Ions
(C) Positive holes
(D) Positive Ions
Correct Answer: [C] Positive holes.

132. The blue color of the sky is due to
(A) Reflection
(B) Dispersal
(C) Scattering
(D) Refraction
Correct Answer: [C] Scattering.

133. Sound waves in air are
(A) Electromagnetic
(B) Polarized
(C) Transverse
(D) Longitudinal
Correct Answer: [D] Longitudinal.

134. Red is used as a danger signal because
(A) red colour is easily available.
(B) red colour is soothing for the eye.
(C) blood is red.
(D) red light is scattered least by the air molecules
Correct Answer: [D] red light is scattered least by the air molecules.

135. A. C is converted to D.C. by
(A) Transformer
(B) Motor
(C) Rectifier
(D) Dynamo
Correct Answer: [C] Rectifier.

136. The closest distance at which a normal person can see an object clearly is
(A) 80 cm.
(B) 25 cm.
(C) 10 cm.
(D) 50 cm
Correct Answer: [B] 25 cm..

137. Solar energy is produced by the process of
(A) Explosion
(B) Contraction
(C) Fusion
(D) Fission
Correct Answer: [C] Fusion.

138. The screen of the cinema hall is always white and rough. Because light rays of all colors falling on the screen suffer
(A) refraction
(B) scattering
(C) total absorption
(D) total reflection
Correct Answer: [B] scattering.

139. With an increase in temperature the resistance of a pure semiconductor
(A) increases
(B) decreases
(C) first increases and then decreases
(D) remains the same
Correct Answer: [B] decreases.

140. The motion of which particle through a metallic wire is called electric current?
(A) Neutron
(B) Photon
(C) Electron
(D) Positron
Correct Answer: [C] Electron.


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