Physics MCQs
Physics Objective (Multiple Choice) General Knowledge & General Science Questions & Answers for SSC-CGL, UPPSC, NDA, CDS and all one day examinations of India.
21. What are infrasonic sounds?
[A] Sounds of frequencies below 20 Hz
[B] Sounds of frequencies above 20 Hz
[C] Sounds of frequencies below 200 Hz
[D] Sounds of frequencies above 20 Hz
Show Answer
Correct Answer: A [Sounds of frequencies below 20 Hz]
Notes:
Sounds of frequencies below 20 Hz are called infrasonic sound or infrasound.
22. Which of the following is the efficiency of a Carnot engine(a = Temperature of source, b=Temperature of sink)?
[A] 1 – b/a
[B] 1 – a/b
[C] 1 + b/a
[D] 1 + a/b
Show Answer
Correct Answer: A [1 – b/a]
Notes:
Carnot engine is a reversible engine operating between two temperatures T1 (source) and T2 (sink). The Carnot cycle consists of two isothermal processes connected by two adiabatic processes. The efficiency of a Carnot engine is given as: 1 – T2/T1
23. Which of the following is true about a concave lens?
[A] power of a concave lens is positive
[B] power of a concave lens is negative
[C] power of a concave lens is zero
[D] None of the above
Show Answer
Correct Answer: B [power of a concave lens is negative]
Notes:
The power of a convex lens is positive and that of a concave lens is negative.
24. What do we call the cell that requires an outside electrical source to drive the non-spontaneous redox reaction?
[A] Voltaic cell
[B] Electrolytic cell
[C] Galvanic cell
[D] None of the above
Show Answer
Correct Answer: B [Electrolytic cell]
Notes:
An Electrolytic cell is one kind of battery that requires an outside electrical source to drive the non-spontaneous redox reaction.
25. What do we call a device which generates electric energy using chemical energy?
[A] Potentiometer
[B] Resistor
[C] Cell
[D] Metre bridge
Show Answer
Correct Answer: C [Cell]
Notes:
A device which generates electric energy using chemical energy is known as a cell.
26. What happens to a bar magnet of dipole moment (m) is placed in a uniform magnetic field (B)?
[A] the force on the bar magnet is zero
[B] the torque on the bar magnet is m × B
[C] Both a and b
[D] None of the above
Show Answer
Correct Answer: C [Both a and b]
Notes:
When a bar magnet of dipole moment m is placed in a uniform magnetic field B: (a) the force on it is zero, (b) the torque on it is m × B, (c) its potential energy is –m.B, where we choose the zero of energy at the orientation when m is perpendicular to B.
27. What are the nuclei of different atoms containing same number of neutrons known as?
[A] Isobars
[B] Isotopes
[C] Isotones
[D] Isomers
Show Answer
Correct Answer: C [Isotones]
Notes:
Nuclei of different atom containing same number of neutrons are called isotones.
28. Which of these dopants is NOT used to increase the conductivity of a semi-conductor?
[A] Indium
[B] Aluminium
[C] Arsenic
[D] Boron
Show Answer
Correct Answer: B [Aluminium]
Notes:
There are two types of dopants used in doping the tetravalent Si or Ge: (i) Pentavalent (valency 5); like Arsenic (As), Antimony (Sb), Phosphorous (P), etc (ii) Trivalent (valency 3); like Indium (In), Boron (B), Aluminium (Al), etc
29. A simple microscope consists of which of the following lenses?
[A] a short focus convex lens
[B] a short focus concave lens
[C] a long focus concave lens
[D] a long focus convex lens
Show Answer
Correct Answer: A [a short focus convex lens]
Notes:
The use of a single short focus convex lens or groups of lenses are found in simple magnification devices such as the magnifying glass, loupes, and eyepieces for telescopes and microscopes. If a convex lens is held close to a person’s eyes, they will see an image that is upright and larger than the actual object.
30. What should a person on a freely rotating turn table do to decrease his (angular) speed ?
[A] Sit down with raised hands
[B] Bring his hands down
[C] Raise his hands up
[D] Spread his hands outwards
Show Answer
Correct Answer: D [Spread his hands outwards]
Notes:
When a person on a turn table will raise his hands, there will be increase in the momentum of inertia. Hence, the angular velocity of the turntable will decrease.
