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. These questions are part of GKToday’s 35000+ MCQs Bank Course in GKToday Android App
21. What is the speed of electromagnetic waves in vacuum?
[A] 1000 m/s
[B] 3 x 108 m/s
[C] 300000 m/s
[D] Different for different waves
Show Answer
Correct Answer: B [3 x 108 m/s]
Notes:
In vacuum, all electromagnetic waves have the same speed whose value is 299, 792, 458 m/s or nearly equal to 3 x 108 m/s.
22. What are ultrasonic sounds?
[A] Sounds of frequencies above 2 KHz
[B] Sounds of frequencies above 20 KHz
[C] Sounds of frequencies above 200 KHz
[D] Sounds of frequencies above 20 Hz
Show Answer
Correct Answer: B [Sounds of frequencies above 20 KHz]
Notes:
Sounds with frequencies higher than 20 kHz are called ultrasonic sound or ultrasound. Ultrasound is produced by dolphins, bats and porpoises.
23. Which of the following are the cases of use of concave mirrors?
[A] Search-lights
[B] Shaving mirrors
[C] Solar furnaces
[D] All of the above
Show Answer
Correct Answer: D [All of the above]
Notes:
Concave mirrors are commonly used: 1. in torches, search-lights and vehicles headlights to get powerful parallel beams of light. 2. as shaving mirrors to see a larger image of the face. 3. by dentists to see large images of the teeth of patients. 4. to concentrate sunlight to produce heat in solar furnaces.
24. On which of the following does the resistance of a conductor depend?
[A] Length
[B] Area of cross-section
[C] Nature of material
[D] All of the above
Show Answer
Correct Answer: D [All of the above ]
Notes:
The resistance of any conductor depends on : 1. its length 2. Area of its cross-section 3. Nature of its material The resistance of a uniform metallic conductor is directly proportional to its length and inversely proportional to its area of cross-section and is given by the formula:
25. What do we call the electrode that can be oxidized or reduced in half reaction?
[A] Inert electrode
[B] Active electrode
[C] Sleeping electrode
[D] Passive electrode
Show Answer
Correct Answer: B [Active electrode]
Notes:
An active electrode is an electrode that can be oxidized or reduced in half reaction.
26. Which of the following is correct about Permeability of free space?
[A] It is a scalar quantity
[B] Its S.I unit is T m A-1
[C] Both a and b
[D] None of the above
Show Answer
Correct Answer: C [Both a and b]
Notes:
The Permeability of free space is a scalar quantity and its S.I. unit is T m A-1.
27. Which of the following nuclear processes is the source of energy output in the interior of stars?
[A] Nuclear Fission
[B] Nuclear Fusion
[C] Both a and b
[D] None
Show Answer
Correct Answer: B [Nuclear Fusion]
Notes:
Thermonuclear fusion is the source of energy output in the interior of stars.
28. Why does an egg sinks in normal water but floats in salty water?
[A] egg increases in salt water
[B] salt water is more dense than normal water
[C] egg decreases in salt water
[D] normal water is more dense than salt water
Show Answer
Correct Answer: B [salt water is more dense than normal water]
Notes:
The fresh egg sinks in fresh water and floats in salt water. The salt water is denser than the fresh water therefore; the egg which is less dense than salt water will float.
29. Which of the following can lead to reduction in friction?
[A] rolling to sliding
[B] potential energy to kinetic energy
[C] dynamic to static
[D] sliding to rolling
Show Answer
Correct Answer: D [sliding to rolling]
Notes:
No force is transferred or modified by a rotating wheel. A wheel reduces friction by allowing the contacting surfaces to roll rather than to drag or slide over each other. By reducing friction, a wheel can enable you to use less force to move an object.
30. Kelvin(K) is the unit of measurement of which of the following?
[A] Pressure
[B] Density
[C] Mass
[D] Temperature
Show Answer
Correct Answer: D [Temperature]
Notes:
The kelvin is the primary unit of temperature measurement in the physical sciences, but is often used in conjunction with the degree Celsius, which has the same magnitude.
