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. 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
22. 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.
23. What is the S.I. unit of power of a lens?
[A] metre
[B] watt
[C] dioptre
[D] second
Show Answer
Correct Answer: C [dioptre]
Notes:
The SI unit of power of a lens is ‘dioptre’. It is denoted by the letter D. If f is expressed in metres, then, power is expressed in dioptres.
24. What is the value of permittivity of free space?
[A] 8.854 × 10–10 C2 N–1 m–2
[B] 8.854 × 10–11 C2 N–1 m–2
[C] 8.854 × 10–12 C2 N–1 m–2
[D] 8.854 × 10–13 C2 N–1 m–2
Show Answer
Correct Answer: C [8.854 × 10–12 C2 N–1 m–2 ]
Notes:
The value of permittivity of free space (ε0) in SI units is 8.854 × 10–12 C2 N–1 m–2.
25. Which of the following cells is the basis of Non-rechargeable batteries?
[A] Galvanic cells
[B] Electrolytic cells
[C] Both a and b
[D] None of the above
Show Answer
Correct Answer: A [Galvanic cells]
Notes:
Non-rechargeable batteries are examples of Galvanic cells.
26. Which of the following is correct?
[A] The nuclear force does not depend on the electric charge
[B] The nuclear force is much weaker than the Coulomb force
[C] Both a and b
[D] None of the above
Show Answer
Correct Answer: A [The nuclear force does not depend on the electric charge]
Notes:
The nuclear force is much stronger than the Coulomb force acting between charges or the gravitational forces between masses. The nuclear force does not depend on the electric charge.
27. In which of these transistors, the two segments of n-type semiconductor are separated by a segment of p-type semiconductor?
[A] p-n-p transistor
[B] n-p-n transistor
[C] Both a and b
[D] None
Show Answer
Correct Answer: B [n-p-n transistor]
Notes:
n-p-n transistor :The two segments of n-type semiconductor (emitter and collector) are separated by a segment of p-type semiconductor (base).
28. Why does an oil drop spread over water?
[A] Because oil is lighter than water
[B] Because oil does not mix with water
[C] Because surface tension of oil is much smaller than that of water
[D] Because oil is more viscous
Show Answer
Correct Answer: C [Because surface tension of oil is much smaller than that of water]
Notes:
The surface tension of the water is more than that of oil.Therefore,when oil is poured over water,the greater value of surface tension of water pulls oil in all directions,and as such it spreads on the water.
29. Which of the following is not a vector quantity?
[A] Displacement
[B] Momentum
[C] Torque
[D] Speed
Show Answer
Correct Answer: D [Speed]
Notes:
Speed, being a scalar quantity, is the rate at which an object covers distance. The average speed is the distance per time ratio. Speed is ignorant of direction. Whereas, vector quantity is a quantity having direction as well as magnitude, especially as determining the position of one point in space relative to another.
30. At what temperature (in degree celsius), the numerical values on Celsius and Fahrenheit scales become equal?
[A] 40
[B] -40
[C] 273
[D] -273
Show Answer
Correct Answer: B [-40]
Notes:
To find the temperature when both are equal, we use an old algebra trick and just set ºF = ºC and solve one of the equations. So the temperature when both the Celsius and Fahrenheit scales are the same is -40 degrees.
