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.
31. Which of the following energy transformation takes place in microphone?
[A] Sound into electrical energy
[B] Electrical into sound energy
[C] Sound into mechanical energy
[D] Mechanical into sound energy
Show Answer
Correct Answer: B [Electrical into sound energy]
Notes:
Microphone is a transducer that converts sound into an electrical energy. Microphones are used in many applications such as telephones, hearing aids, public address systems for concert halls and public events, motion picture production, live and recorded audio engineering, sound recording, radio and television broadcasting.
32. Why does man weigh more at the poles than at the equator?
[A] Because there is no atmosphere at the poles
[B] Because gravitational pull is more at the poles
[C] Because gravitational pull is less at the poles
[D] None of the above
Show Answer
Correct Answer: B [Because gravitational pull is more at the poles]
Notes:
If we see the shape of the Earth, it is flatter at the poles and bulged at the equator. Therefore, the distance of the poles from the centre of the Earth is less than distance of the equator from the centre of the Earth. Now, recall the formula of gravitational force between two objects —F = (G * M1 * M2)/R^2. Here, R is the distance between the two objects. Distance is inversely proportional to the Force. Since the distance at the equator is more, it will have less gravitational force. Lesser the gravitational force, lesser will be the weight of the object. Since the distance between the poles is less, there will be more gravitational force. More is the gravitational force, more will be the weight of the object. Hence, the object will weigh minimum at the equator and maximum at the poles.
33. Optical fibre works on which of the following principles?
[A] total internal reflection
[B] refraction
[C] scattering
[D] interference
Show Answer
Correct Answer: A [total internal reflection]
Notes:
Fiber optic cables work because of the principle of total internal reflection. Therefore, if lights hit the sides of the cable at an angle greater than the critical angle, it will be bounced back into the cable.
34. When an air bubble at the bottom of a lake rises to the top, which of the following will happen to it?
[A] Increase in size
[B] decrease in size
[C] maintain its size
[D] flatten into a disk-like shape
Show Answer
Correct Answer: A [Increase in size]
Notes:
Pressure starts decreasing as we go upwards. That is the reason that air bubble in water grow in size when it rises from bottom to top. As the pressure exerted by water is directly proportional to the depth of water, as the depth of water increases in a water body, the pressure increases linearly.
35. Which one is the minimum possible temperature beyond which matter cannot be cooled?
[A] -98.10° C
[B] -100.00° C
[C] -273.15° C
[D] -459.40° C
Show Answer
Correct Answer: C [-273.15° C]
Notes:
At the physically impossible-to-reach temperature of zero kelvin, or minus 459.67 degrees Fahrenheit (minus 273.15 degrees Celsius), atoms would stop moving. As such, nothing can be colder than absolute zero on the Kelvin scale.
36. Which quantity is measured using bolometer?
[A] Intensity of sound
[B] Intensity of electromagnetic radiation
[C] Intensity of pain
[D] Intensity of wind movement
Show Answer
Correct Answer: B [Intensity of electromagnetic radiation]
Notes:
When electromagnetic radiation of a particluar frequency is incident on bolometer’s temperature dependent resistance, which results in the rise in temperature and using this the intensity of the radiation can be calculated.
37. What will happen when a strong beam of light is passed through a colloidal solution?
[A] Light will be scattered
[B] Light will pass unchanged
[C] Light will be absorbed
[D] Light will be reflected
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Correct Answer: A [Light will be scattered]
Notes:
When a strong beam of light is passed across a colloidal solution, it undergoes scattering caused by the suspended particles present in it. This effect of scattering of light incident on colloidal solution is called Tyndall effect.
38. What will be the weight of a body at the centre of earth?
[A] half the weight at the surface
[B] zero
[C] twice the weight at the surface
[D] infinite
Show Answer
Correct Answer: B [zero]
Notes:
Weight of a body is the force with which it is attracted towards the centre of earth. The weight of a body, ‘W’ of mass ‘m’ is given by: W = mg, where ‘g’ is the acceleration due to gravity. At the centre of earth, value of ‘g’ is zero. Therefore, weight of a body will be zero at the centre of the earth.
39. Water will not be vaporized if__:
[A] the temperature is 0°C
[B] the humidity is 0%
[C] the humidity is 100%
[D] the temperature is 100°C
Show Answer
Correct Answer: C [the humidity is 100%]
Notes:
If the relative humidity is 100 percent, water will not evaporate as the air is already saturated with moisture. When relative humidity approaches 100 percent, condensation can occur. The lower the relative humidity, the easier it is for moisture to evaporate. Therefore, people living in hot coastal areas suffen from heat stagnation.
40. Velocity of sound in air does not depend on__:
[A] Density of air
[B] Temperature of air
[C] Pressure of air
[D] Humidity of air
Show Answer
Correct Answer: C [Pressure of air]
Notes:
Assuming air to be an ideal gas, the speed of sound depends on temperature only. As air temperature increases, so does the speed of sound and vice versa. The speed of sound is completely independent of air pressure because the air pressure and air density are proportional to each other at the same temperature. The speed of sound in air depends on the density of air which in turn depends on the temperature.
