43. Science for NDA / CDS / AFCAT

• 0 Questions answered correctly
• 0 Questions answered incorrect
• 10 Questions unattempted

• 1

  For which Diode is used ? 

   

   

  • A

    (a) modulation      

     

  • B

    (b) oscillation 

     

  • C

    (c) amplification   

     

  • D

    (d) purification 

     

  Explanation

  Correct answer: (d) purification
  Explanation:

  • A diode is primarily used for rectification, which means converting alternating current (AC) to direct current (DC). This process can be loosely referred to as "purification" because it eliminates the negative half-cycles of the AC signal.
  • Incorrect options:

  (a) Modulation: Modulation is achieved using transistors or specific circuits.

  (b) Oscillation: Oscillators require active devices like transistors or operational amplifiers, not diodes.

  (c) Amplification: Amplification is performed using transistors or operational amplifiers.

• 2

  Who among the following developed the technology of underground nuclear explosion? 

   

   

  • A

    (a) Dr. Homi J. Bhabha 

     

  • B

    (b) Dr. Vikram Sarabhai 

     

  • C

    (c) Dr. Raja Ramanna 

     

  • D

    (d) Dr. P. K. Iyengar 

     

  Explanation

  Correct answer: (d) Dr. P. K. Iyengar
  Explanation:

  • Dr. P. K. Iyengar was a leading scientist in India's nuclear program and played a pivotal role in developing the underground nuclear explosion technology, contributing to India's first successful nuclear test, "Smiling Buddha," in 1974.
  • Incorrect options:
    • (a) Dr. Homi J. Bhabha: Known as the father of India's nuclear program, but he did not develop underground nuclear technology.
    • (b) Dr. Vikram Sarabhai: Known for his work in space research, particularly as the founder of ISRO.
    • (c) Dr. Raja Ramanna: He was part of the nuclear program but not specifically credited with underground nuclear explosions.
• 3

  Which among the following types of coal produces most heat per unit ? 

   

              

  • A

    (a) Coal 

     

  • B

    (b) Lignite 

     

  • C

    (c) Anthracite        

     

  • D

    (d) Pit 

  Explanation

  Correct answer: (c) Anthracite
  Explanation:

  • Anthracite is the highest grade of coal with the highest carbon content, leading to maximum heat production.
  • Incorrect options:
    • (a) Coal: A generic term for all types of coal.
    • (b) Lignite: A lower-grade coal with higher moisture content and less carbon.
    • (d) Pit: This is not a type of coal but rather refers to coal mining sites.
• 4

  Which among the following waves is used for communication by artificial satellites ? 

   

             

  • A

    (a) Micro waves 

     

  • B

    (b) Radio waves 

     

  • C

    (c) Amplitude Modulation (AM) 

     

  • D

    (d) Frequency of 10 series 

     

  Explanation

   Correct answer: (a) Micro waves
  Explanation:

  • Microwaves have a high frequency and short wavelength, allowing efficient communication with satellites due to low atmospheric interference.
  • Incorrect options:
    • (b) Radio waves: Used for terrestrial communication but not efficient for satellite communication.
    • (c) Amplitude Modulation (AM): A method of encoding signals, not a type of wave.
    • (d) Frequency of 10 series: This is unclear and not applicable.
• 5

  What is found in frequency modulation? 

   

   

  • A

    (a)   Fixed frequency 

     

  • B

    (b)   Fixed dimension 

     

  • C

    (c)   Change in frequency and dimension 

     

  • D

    (d)   Change in dimension only 

  Explanation

  Correct answer: (c) Change in frequency and dimension
  Explanation:

  • In frequency modulation (FM), the frequency of the carrier wave changes in accordance with the amplitude of the input signal, while its amplitude remains constant.
  • Incorrect options:
    • (a) Fixed frequency: Frequency changes in FM.
    • (b) Fixed dimension: Dimension does not change, frequency does.
    • (d) Change in dimension only: Frequency modulation affects frequency, not dimensions alone.
• 6

  When the speed of car is doubled, then what will be the breaking force of the car to stop it in the same distance ? 

   

   

  • A

    (a) four times        

     

  • B

    (b) two times 

     

  • C

    (c) half     

     

  • D

    (d) one-fourth 

  Explanation

  Correct answer: (a) Four times
  Explanation:

  • Kinetic energy (KE) =, so doubling the speed increases the kinetic energy by four times. To stop the car in the same distance, the braking force must also increase by four times.
  • Incorrect options:
    • (b) Two times: Incorrect, as energy is proportional to the square of the velocity.
    • (c) Half: Incorrect, braking force increases, not decreases.
    • (d) One-fourth: Incorrect, the force needs to increase, not decrease.
• 7

  The dimension of which of the following is the same as that of impulse ? 

   

  • A

    (a) Volume             

     

  • B

    (b) Momentum 

     

  • C

    (c) Torque              

     

  • D

    (d) Change in the rate of momentum

  Explanation

  

• 8

  Which among the following is the fundamental quantity ? 

   

  • A

    (a) Volume             

     

  • B

    (b) Time 

     

  • C

    (c) Velocity             

     

  • D

    (d) Force

  Explanation

  

• 9

  When a ring of metal is heated what happens to its hole? 

   

              

  • A

    (a)   expands 

     

  • B

    (b)   contracts 

     

  • C

    (c)   it expands or contracts according

     

  • D

    (d)   it expands or contracts according to its coefficient of expansion 

  Explanation

  Correct answer: (a) Expands
  Explanation:

  • When a metal ring is heated, it expands uniformly. The hole expands as if it were filled with the same material.
  • Incorrect options:
    • (b) Contracts: Incorrect, as the entire ring expands.
    • (c) It expands or contracts according to its coefficient of expansion: Misleading, the hole always expands.
    • (d) It expands or contracts depending: Misleading, the hole expands irrespective of other factors.
• 10

  If the diameter of a capillary is doubled, then the rise of water in it will be 

   

  • A

    (a) two times       

  • B

    (b) half 

     

  • C

    (c) four times      

  • D

      (d) no change

  Explanation