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 is the S.I unit of frequency?
[A] Second
[B] Watt
[C] Hertz
[D] Joule
Show Answer
Correct Answer: C [Hertz]
Notes:
The frequency is defined as the number of periodic motions executed by body per second. The S.I unit of frequency is hertz (Hz).
22. What is the speed of electromagnetic waves in vacuum?
[A] 1000 m/s
[B] 3 x 108 m/s
[C] 300000 m/s
[D] Different for different waves
Show Answer
Correct Answer: B [3 x 108 m/s]
Notes:
In vacuum, all electromagnetic waves have the same speed whose value is 299, 792, 458 m/s or nearly equal to 3 x 108 m/s.
23. Which of the following waves are also called as heat waves?
[A] UV rays
[B] X-rays
[C] Infrared
[D] Micro waves
Show Answer
Correct Answer: C [Infrared]
Notes:
Infrared waves vibrate not only the electrons, but entire atoms or molecules of a substance. This vibration increases the internal energy and consequently, the temperature of the substance. Therefore, infrared waves are often called as heat waves.
24. What do we call the magnitude of the maximum disturbance in the medium on either side of the mean value called as?
[A] Frequency
[B] Angular Displacement
[C] Amplitude
[D] Wave number
Show Answer
Correct Answer: C [Amplitude]
Notes:
The magnitude of the maximum disturbance in the medium on either side of the mean value is called the amplitude of the wave. It is usually represented by the letter A.
25. What is the effect of increase of temperature on the speed of sound?
[A] it increases
[B] it decreases
[C] it may or may not increase
[D] No effect
Show Answer
Correct Answer: A [it increases]
Notes:
In any medium as we increase the temperature the speed of sound increases. For example, the speed of sound in air is 331 m s–1 at 0 ºC and 344 m s–1 at 22 ºC.
26. Which of the following is correct about the speed of the sound, at same temperature?
[A] sound travels faster in humid air than in dry air
[B] sound travels slower in humid air than in dry air
[C] speed of sound is same in humid air and dry air
[D] None of the above
Show Answer
Correct Answer: A [sound travels faster in humid air than in dry air]
Notes:
With increase in humidity, density of air decreases. So with rise in humidity velocity of sound increases. This is why sound travels faster in humid air (rainy season) than in dry air (summer) at the same temperature.
27. What do we call the temperature and pressure at which solid, liquid, and vapor phases of a particular substance coexist in equilibrium?
[A] Equilibrium point
[B] Triple point
[C] Normal point
[D] None of the above
Show Answer
Correct Answer: B [Triple point]
Notes:
the triple point is the temperature and pressure at which solid, liquid, and vapor phases of a particular substance coexist in equilibrium.
28. Which of the following are Green house gases?
[A] Carbon dioxide
[B] Methane
[C] Nitrous oxide
[D] All of the above
Show Answer
Correct Answer: D [All of the above]
Notes:
Some of the green house gases: carbon dioxide, methane, nitrous oxide, chlorofluorocarbon, tropospheric ozone.
29. Which of the following exchanges with the surrounding take place in a closed system?
[A] Both matter and energy
[B] Only energy
[C] Only matter
[D] No exchange
Show Answer
Correct Answer: B [Only energy]
Notes:
In a closed system, only energy is exchanged with the surrounding.
30. Which of the following is true about the focal length of a spherical mirror?
[A] it is equal to its radius of curvature
[B] it is equal to half its radius of curvature
[C] it is equal to twice its radius of curvature
[D] None of the above
Show Answer
Correct Answer: B [it is equal to half its radius of curvature]
Notes:
The focal length of a spherical mirror is equal to half its radius of curvature.
