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# Physics MCQ Questions  with Answer for all Competitive Exams

 Physics MCQ Questions  with Answer

Q91. The Law of Inertia is also known as _____.

(a) Newton’s first law of motion

(b) Newton’s second law of motion

(c) Newton’s third law of motion

(d) None of these

 Answer: (a)Explanation: Law of Inertia is also known as Newton’s First Law of Motion. Newton’s First Law of Motion states that an object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless an external force applied to it.

Q92. What happens to a liquid, when the vapor pressure equals the atmospheric pressure?

(a) The liquid cools

(b) The liquid boils

(c) No change

(d) The liquid evaporates

 Answer: (b)Explanation: The condition when the vapor pressure of the liquid is equal to the atmospheric pressure is termed as Boiling. Hence at that temperature, the liquid boils.

Q93. Assertion (A): The boiling point of water decreases as the altitude increases.

Reason (R): The atmospheric pressure increases with altitude.

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

(b) Both A and R are true but it 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: The boiling point of an element or a substance is the temperature at which the vapour pressure of the liquid equals the environmental pressure surrounding the liquid. As altitude increases atmospheric pressure decreases, so the boiling point decreases, so the liquid would boil at a lower temperature.

Q94. Ultrasonics is sound waves of frequency ​

(a)​ Greater than 20,000 Hz ​

(b) ​Less than 10,000 Hz ​

(c)​ Equal to 1000 Hz

​(d) ​None of these

 Answer: ​(a)​Explanation: Ultrasonic is defined as acoustic frequencies greater than 16-20 kHz up to 1 GHz and is not audible to the human ear.

Q95. Which of the following is not scalar quantity? ​

(a)​ Time ​

(b)​ Volume ​

(c)​ Density ​

(d) ​Momentum

 Answer: ​(d)​Explanation: Momentum is a vector quantity. A vector quantity possesses both a magnitude and a direction.

Q96. An image formed by a concave mirror on a screen is called __________?

(a) Virtual image

(b) Real image

(c) Inverted image

(d) Erect image

 Answer: (b)Explanation: Concave mirror forms a real and inverted image of an object.

Q97. A hollow sphere of radius R, a hollow cube of side 12, and a thin circular plate of radius R, made up of the fame material, are all heated to 20°C above room temperature. When left to cool in the room, which of them will reach the room temperature first?

(a) Circular plate

(b) Cube

(c) Sphere

(d) All of them, will reach the room temperature at the same time

 Answer: (c)Explanation: The loss of heat is directly proportional to the surface area, hence loss of hoot will be earlier in the case of sphere because it has the maximum surface area.

Q98. Which electromagnetic radiation is used for satellite communication?

(a) Ultraviolet

(b) Infrared

(c) Microwave

(d) Millimeter-wave

 Answer: (c)Explanation: Microwaves have short wavelengths and high frequency, hence they pass through the earth’s atmosphere and can reach to satellite easily.

Q99. Cloudy nights are warmer compared to clear cloudless nights because clouds:

(a) Prevent clod waves from the sky from descending on earth

(b) Reflect back the heat given off by the earth

(c) Produce heat and radiate it towards the earth

(d) Absorb heat from the atmosphere and send it towards the earth

 Answer: (b)Explanation: Cloudy nights are warmer than clear nights because the cloud cover provides a shield that acts as an insulator and stores up the heat radiated by the earth and do not permit heat to escape.

Q100. When we hear a sound, we can identify its source from

(a) Wavelength of sound

(b) The overtones present in the sound

(c) The intensity of sound

(d) The amplitude of the sound

 Answer: (b)Explanation: The overtones present in the sound give us knowledge of the source as every source has fixed fundamental frequency. When instruments are played above fundamental frequency overtones can be recognized.

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