Physics MCQ Questions  with Answer for all Competitive Exams

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Physics MCQ Questions  with Answer
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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.

Cade:

(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

(c) Lead

(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 travelling 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 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 images in the desert and the operation of optical fibres. The formation of images in the microscope and the 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.

Q61. How much mechanical work must be done to completely melt 1 gram of ice at 0°C?

(a) 4.2 J

(b) 80 J

(c) 336 J

(d) 2268 J

Answer: (c)

Explanation: Work done to completely melt 1 gm of ice at 0°C

W = Q = ML

W = 1 × 336 J/gm = 336 J

Where L = (Latent heat of fusion for water)

Q62. Which once, the following is printed on a commonly used fluorescent tube light?

(a) 220K

(b) 273K

(c) 6500 K

(d) 9000 K

Answer: (c)

Explanation: A fluorescent lamp or fluorescent tube is a gas-discharge lamp that uses electricity to excite mercury vapour. The excited mercury atoms produce short-wave ultraviolet light that then causes a phosphor to fluoresce, producing visible light. 6500K is usually printed on a used fluorescent tube light.

Q63. Consider the following statements:

In a nuclear reactor, a self-sustained chain reaction is possible, because:

  1. More muttons are released in each of the fission reactions.
  2. The neutrons immediately take part in the fission process.
  3. The fast neutrons are slowed down by graphite.
  4. Every neutron released in the fission reaction initiates further fission.

Which of these statements are correct?

(a) 1, 2 and 3

(b) 1 and 3

(c) 2 and 4

(d) 2, 3 and 4.

Answer: (a)

Explanation: A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. The most commonly used nuclear reactors are for the generation of electrical power and for the power in some ships. In every fission reaction in which uranium nuclei split up to give smaller nuclei three more neutrons are produced which further results in the splitting of heavy uranium nuclei and more neutrons will be produced. The statement, 1 and 2 are correct. In a nuclear reactor, all the neutrons produced cannot take pan in fission reaction, else the reaction can turn out extremely violent. Thus, graphite rods are used as a control rod to slow down the speed of fast-moving neutrons. Thus, statement 3 is also correct.

Q64. Equation E = p.c. is valid for –

​(a) ​Both electron and Photon ​

(b)​ Electron only ​

(c)​ Photon only

​(d) ​Neither electron nor photon

Answer: (c)​

Explanation: The equation E = p.c. is valid for particles with zero rest mass, which is valid for photons but not for electron

Q65. A brass ball is tied to a thin wire and swung so as to move uniformly in a horizontal circle. Which of the following statements in this regard is/are true? ​

1.​ The ball moves with constant velocity ​

2.​ The ball moves with constant speed ​

3.​ The ball moves with constant acceleration

4.​ The magnitude of the acceleration of the ball is constant ​

Select the correct answer using the code given below:

​(a)​ 1 only ​

(b) ​1 and 3 ​

(c)​ 1, 2 and 4

​(d)​ 2 and 4 only

Answer: ​(d)

Explanation: ​Velocity is the vector quantity so it gets changed as the direction changes. The ball will move with constant speed and the magnitude of the acceleration of the ball will also be constant.

Q66. The final image is a simple microscope that is

(a) Real, diminished, and inverted

(b) Real, magnified, and erect

(c) Virtual, magnified, and erect

(d) Virtual, diminished and erect

Answer: (c)

Explanation: Simple microscope uses a biconvex lens which forms an enlarged, erect, and virtual image of the object.

Q67. The boiling point of a liquid varies as

(a) Pressure varies

(b) Temperature varies

(c) Volume varies

(d) Density varies

Answer: (a)

Explanation: On increasing pressure, the boiling point increases. On decreasing pressure, the boiling point decreases.

Q68. Consider the following statements:

  1. A geostationary satellite is at an approximate height of 10.000 km.
  2. FM transmission of music is of very good quality because the atmospheric or man-made noises which are generally frequency variations can do little harm.

Which of the statements given above is correct?

(a) 1 only

(b) 2 only

(c) Both 1 and 2

(d) Neither 1 nor 2

Answer: (a)

Explanation: On increasing pressure, the boiling point increases. On decreasing pressure, the boiling point decreases.

Q69. ​Match List-I with List-II and select the correct answer with the help of codes given below:

List-IList-II
A. Temperature1. Kelvin
B. Power2. Watt
C. Pressure3. Pascal
D. Force4. Newton

Codes: A B C D

(a)        2 1 3 4

(b)       1 2 4 3

(c)        1 2 3 4

(d)       2 1 4 3

Answer: ​(c)

Explanation: ​The unit of temperature is Kelvin, power is measured in watt, pressure in Pascal, and force in newton.

Q70. A myopic eye can be corrected by using a

​(a)​ Convex lens ​

(b)​ Concave lens ​

(c)​ Cylindrical lens ​

(d) ​Plano-convex lens

Answer: (b) ​

Explanation: Near-sightedness or myopia is the inability of the eye to focus on distant objects. The near-sighted eye has no difficulty viewing nearby objects. This condition results if the light from distant objects is refracted more than is necessary. The cure for the near-sighted eye is to equip it with a diverging or concave lens. Since the nature of the problem of near-sightedness is the light before it reaches the eye. This light will then be converted by the cornea and lens to produce an image on the retina.

Q71. When the length of the tube of a microscope is increased, its magnifying power –

(a) ​Decreases ​

(b) ​Increases ​

(c)​ Remains constant ​

(d)​ None of the above

Answer: ​(b)

Explanation: ​Increasing the length of the tube will increase the magnifying power as Magnifying power α length of the tube and given by the formula M = L/Fo (1+ D/fe)

Q72. A light-year is a unit of

(a) Time

(b) Distance

(c) Speed of light

(d) Intensity of light

Answer: (b)

Explanation: Light year is the distance travelled by light in one year in space.

Q73. With reference to ‘fuel cells’ in which hydrogen-rich fuel and oxygen are used to generate electricity. Consider the following statements:

  1. If pure hydrogen is used as a fuel, the fuel cell emits heat and water as by-products.
  2. Fuel eels can be used for powering buildings and not for small devices like laptop computers.
  3. Fuel cells produce electricity in the form of Alternating Current (AC).

Which of the statements given above is/are correct?

(a) 1 only

(b) 2 and 3 only

(c) 1 and 3 only

(d) 1, 2 and 3

Answer: (a)

Explanation: When pure hydrogen is used as fuel. The only by-products generated from the fuel cell are pure water and heat. Similar to a battery a fuel cell with a supply of hydrogen and oxygen can be used to power devices that use electricity.

Q74. The objective in a reflecting telescope is – ​

(a)​ Concave mirror​ ​

(b)​ Convex mirror ​

(c)​ Prism

​(d)​ Concavo – Convex lens

Answer: (a)​

Explanation: Concave mirrors are used as an objective in reflecting telescopes.

Q75. The tail of a comet is directed away from the sun because:

(a) As the comet rotates around the sun, the lighter mass of the comet is pushed away due to the centrifugal force alone

(b) As the comet rotates, the lighter mass of the comet is attracted by some stars situated in the direction of its tail

(c) The radiation emitted by the sun exerts a radial pressure on the comet throwing its tail away from the sun

(d) The tail of the comet always exists in the same orientation

Answer: (c)

Explanation: The radiation emitted by the sun exerts radial pressure on the comet. So the tail of the comet is always directed away from the sun.

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