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# Physics MCQ Questions  with Answer for all Competitive Exams

Q51. Which of the following force is a virtual force?

(a) Centripetal force

(b) Centripetal Reaction force

(c) Centrifugal force

(d) Strong Nuclear force

 Answer: (c)Explanation: Centrifugal force is an inertial/pseudo force that is acted upon an object moving in a curved path. It acts outwardly away from the centre of rotation.

Q52. The weight of a body acts through the centre of

(a) Gravity

(b) Mass

(c) Both (1) and (2)

(d) Buoyancy

 Answer: (a)Explanation: Centre of gravity is defined as a point at which the entire weight of a body is concentrated.

Q53. The instrument used to change the speed of the electric fan –

(a) Amplifier

(b) Regulator

(c) Switch

(d) Rectifier

 Answer: (b)Explanation: The regulator is used to change the speed of the fan.

Q54. Assertion (A): In a motion picture, usually 24 frames are projected every second over the whole length of the film.

Reason (R): An image formed on the retina of the eye persists for about 0.1 s after the removal of the stimulus.

(a) Both A and R are true and R is the correct explanation of A

(b) Both A and R are true but R is not a correct explanation of A

(c)  A is true but R is false

(d) A is false but R is true

 Answer: (c)Explanation: A is correct but an image formed on the retina of 1 eye persists for about —1/16 sec (0.06sec) after it changes.

Q55. Optical fibre works on the principle of ​

(a) ​Total internal reflection

​(b) ​Refraction

​(c) ​Scattering

​(d)​ Interference

 Answer: ​(a)​Explanation: Optical fibre works on the principle of total internal reflection. Each fibre consists of core and cladding. The Refractive index of the core is greater than the cladding.

Q56. The filament of an electric bulb is made up of–

(a) Copper

(b) Nichrome

(d) Tungsten

 Answer: (d)Explanation: The filament of an electric bulb is made up of tungsten. It has a high melting point and great tensile strength.

Q57. Assertion (A): Small glass beads toed on traffic signals glow brightly when light falls upon them.

Reason (R): Light is totally reflected when the angle of incidence exceeds a certain critical value and light traveling in a denser medium is reflected from a rarer medium.

Codes: (a) Both A and R are true and R is the correct explanation of A

(b) Both A and R are true but R is not a correct explanation of A

(c) A Ls true but R is false

(d) A is false but R is true

 Answer: (a)Explanation: Both of the statements are correct and statement 2 is also a correct explanation for statement 1. Total internal reflection is an optical phenomenon that happens when a ray of light strikes a medium boundary at an angle larger than a particular critical angle with respect to the normal to the surface. If the refractive index is lower on the other side of the boundary, no light can pass through and all of the light is reflected. Thus because of this phenomenon, traffic light beads glow when light falls on them.

Q58. The least distance of distinct vision for the human eye is ​

(a) ​25 cm

​(b)​ 5 cm

​(c) ​75 cm ​

(d) ​100 cm

 Answer: (a)​Explanation: The least distance of distinct vision is 25 cm. It is the minimum distance that the eye can accommodate to see the object.

Q59. Consider the following statement: ​The principle of total internal reflection is applicable to explain the ​

1.​ Formation of mirage in the desert. ​

2.​ Formation of the image in the microscope. ​

​3. Colour of the evening sky. ​

4. ​Operation of optical fibres. ​

Which of the statement given above are correct? ​

(a) ​1 and 4 ​

(b)​ 3 and 4 ​

(c)​ 2 and 3 ​

(d)​ 1 and 2

 Answer: (a)​Explanation: The principle of total internal reflection is applicable to explain the formation of image in the desert and the operation of optical fibres. The formation of images in the microscope and colour of the evening sky is based on the refraction of light.

Q60. Therm is the unit of

(a) Power

(b) Heat

(c) Light

(d) Distance

 Answer: (b)Explanation: Therm is the non-SI unit of heat, just as Celsius and Fahrenheit are of temperature.

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