Physics MCQ Questions  with Answer for all Competitive Exams

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Physics MCQ Questions  with Answer

Q71. When the length of the tube of a microscope is increased, it’s 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 traveled 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 a radial pressure on the comet. So the tail of the comet is always directed away from the sun.

Q76. A ‘black hole’ is a body in space that does not allow any radiation to come out. This property is due to its:

(a) Very small size

(b) Very large size

(c) Very high density

(d) Very low size

Answer: (c)

Explanation:  A black hole is a region of space from which nothing not even light, can escape. It is the result of the deformation of space-time caused by a very compact mass. The simplest black hole has mass but neither electric charge nor angular momentum. The mass of a black hole is finite, the reason why a black hole has infinite density is that its mass is concentrated into a space of zero-volume. Thus, it has a very high density.

Q77. When a ray of light enters a glass slab, then

​(a) ​Only the frequency changes ​

(b)​ Frequency and velocity change ​

(c)​ Frequency does not change ​

(d) ​Frequency and wavelength change

Answer: (c)​

Explanation: As the light enters from rarer medium to the denser medium the speed of light decreases but the frequency remains the same.

Q78. Match List I with List-II and select the correct answer using the code given below the Lists:​​

List-I (Physical quantity)List-II (Unit)
A. Distance1. Mole
B. Amount of material2. Coulomb
C. Amount of electrical charge3. Light year
D. energy4. Watt-hour

Code: A B C D

(a)        3 1 2 4

(b)       3 2 1 4

(c)        4 2 1 3

(d)       4 1 2 3

Answer: ​(a)​

Explanation: Large distance is measured in a light year. The amount of material is measured by a mole. The amount of electrical charge is measured in the coulomb. Energy is measured in watt-hour.

Q79. The ozone layer above the surface of Earth provides a shield against

(a) X-rays

(b) Ultra Violet Rays

(c) Gamma Rays

(d) Infrared Rays

Answer: (b)

Explanation: The ozone layer consists of O3 molecules, it protects the earth’s atmosphere from harmful ultra-violet rays.

Q80. Which of the following is not a part of a CRT?

(a) Phosphor Screen

(b) Shadow Mask

(c) Electron Gun

(d) Gas Plasma

Answer: (d)

Explanation: In cathode ray tube images are produced when an electron beam strikes a phosphor-coated screen. Its basic components are an electron gun, deflecting coils, phosphor-coated screen, shadow mask, etc.

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