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 happens to a body when its density is equal to the density of the fluid?
[A] it floats
[B] it sinks
[C] it remains suspended
[D] None of the above
Show Answer
Correct Answer: C [it remains suspended]
Notes:
If the buoyant force equals the object’s weight, the object will remain suspended at that depth. If the buoyant force is greater than the object’s weight, the object will rise to the surface and float. If the buoyant force is less than the object’s weight, the object will sink. The buoyant force is always present whether the object floats, sinks, or is suspended in a fluid.
22. What will be the buoyant force acting on the stone, on being immersed in water, if it displaces 100gms of water?
[A] 1000 gm-weight
[B] 100 gm-weight
[C] 10 gm-weight
[D] 1 gm-weight
Show Answer
Correct Answer: B [100 gm-weight]
Notes:
As per Archimedes’ principle, if a stone, on being immersed in water, displaces 100gms of water, the buoyant force acting on the stone will be equal to 100gm-weight.
23. What is the unit of surface tension in c.g.s system?
[A] N/m
[B] dyne/cm
[C] erg/cm
[D] dyne cm
Show Answer
Correct Answer: B [dyne/cm]
Notes:
The unit of surface tension is S.I system is N/m and in c.g.s system is dyne/cm. It is represented by T = force/length.
24. Which of the following instruments is used to measure the relative density of a liquid?
[A] Hydrometer
[B] Hygrometer
[C] Lactometer
[D] Gravitimeter
Show Answer
Correct Answer: A [ Hydrometer ]
Notes:
A hydrometer is an instrument used to measure the specific gravity or relative density of liquids, i.e. the ratio of the density of the liquid to the density of water.
25. What is the relation between frequency(ν) and angular frequency(ω) of a wave?
[A] ν = π/ω
[B] ν = π/ω
[C] ν = 2πω
[D] ν = 2π/ω
Show Answer
Correct Answer: C [ν = 2πω]
Notes:
The frequency ν is the number of oscillations per second and it is related to the angular frequency(ω) as ν = 2πω.
26. What is the process known as when substance converts from the solid to the vapour state directly?
[A] Vaporisation
[B] Sublimation
[C] Regelation
[D] None of the above
Show Answer
Correct Answer: B [Sublimation]
Notes:
The change from solid state to vapour state without passing through the liquid state is called sublimation. Example: Dry ice (solid CO2).
27. 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.
28. 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.
29. What number does orange colour represent in the resistance colour code?
[A] 1
[B] 2
[C] 3
[D] 4
Show Answer
Correct Answer: C [3 ]
Notes:
The resistors have a set of co-axial coloured rings on them. The first two bands from the end indicate the first two significant figures of the resistance in ohms. The third band indicates the decimal multiplier. The last band stands for tolerance or possible variation in percentage about the indicated values.
30. What is the equivalent internal resistance of a series combination of n cells?
[A] the arithmetic mean of their internal resistance
[B] the product of their individual internal resistance
[C] the sum of their individual internal resistance
[D] the sum of the reciprocal of their individual internal resistance
Show Answer
Correct Answer: C [the sum of their individual internal resistance]
Notes:
The equivalent internal resistance of a series combination of n cells is just the sum of their internal resistances.
