38. Science for NDA / CDS / AFCAT

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

• 1

  What is the correct ascending order for frequencies of the following radiations ?

  1. Visible          2. X-rays

  3. Ultraviolet     4. Radio waves

   

   

  • A

    (a) 1, 3, 2, 4    

  • B

     (b) 3, 2, 4, 1

     

  • C

    (c) 4, 1, 3, 2    

  • D

     (d) 4, 3, 1, 2

  Explanation

  Correct Answer: (c) 4, 1, 3, 2

  • Radio waves have the lowest frequency, followed by visible light, ultraviolet, and finally X-rays, which have the highest frequency. The frequency order is directly related to energy, with radio waves being the least energetic and X-rays being highly energetic.
• 2

  Nuclear fission is caused by the impact of :

   

   

  • A

    (a) proton        

  • B

     (b) electron

     

  • C

    (c) neutron      

  • D

     (d) none of these

  Explanation

  Correct Answer: (c) neutron

  • Nuclear fission occurs when a heavy nucleus (e.g., Uranium-235) absorbs a neutron, becoming unstable and splitting into smaller nuclei, releasing a massive amount of energy along with additional neutrons.
• 3

  Which of the following is used as a coolant in nuclear reactors ?

   

   

  • A

    (a) Heavy water 

     

  • B

    (b) Cadmium

     

  • C

    (c) Liquid sodium         

     

  • D

    (d) Graphite

     

  Explanation

  Correct Answer: (c) Liquid sodium

  • Liquid sodium is used as a coolant in nuclear reactors because of its high thermal conductivity, which ensures efficient heat transfer, and its ability to remain liquid over a wide temperature range.
• 4

  Which of the following is good nuclear fuel ?

   

  • A

    (a) Uranium-238            

     

  • B

    (b) Neptunium-239

     

  • C

    (c) Thorium-236            

     

  • D

    (d) Plutonium-239

     

  Explanation

  Correct Answer: (d) Plutonium-239

  • Plutonium-239 is a fissile material, meaning it can sustain a chain reaction. Other isotopes, like Uranium-238, are not fissile and require conversion to Uranium-235 or other fissile isotopes.
• 5

  What is the wavelength of visible spectrum ?

   

   

  • A

    (a) 1300-3000 Å

  • B

    (b) 3900-7600 Å

     

  • C

    (c) 7800-8000 Å

     

  • D

    (d) 8500-9800 Å

     

  Explanation

  Correct Answer: (b) 3900-7600 Å

  • The visible spectrum of light lies within the wavelength range of 3900 Å (violet) to 7600 Å (red). This range defines the portion of the electromagnetic spectrum visible to the human eye.
• 6

  In an atomic explosion, enormous energy is released which is due to the :

   

   

  • A

    (a) conversion of neutrons into protons

     

  • B

    (b) conversion of chemical energy into heat energy

     

  • C

    (c) conversion of chemical energy into nuclear energy

     

  • D

    (d) conversion of mass into energy

     

  Explanation

  Correct Answer: (d) conversion of mass into energy

  • In an atomic explosion, the energy is released according to Einstein's equation E=mc2, where a small amount of mass is converted into an enormous amount of energy.
• 7

  Which of the following statements are correctly associated with ultrasonic waves?

  1. These are the acoustic waves of frequencies more than 20,000 Hertz.

  2. When possible to use, these waves are preferred over X-rays for getting an image of internal organs because they are not harmful.

  3.  Their velocity is more than the velocity of sound.

   

   

  • A

    (a) 1 only       

  • B

    (b) 1 and 2

     

  • C

    (c) 2 and 3      

  • D

      (d) 1 and 3

  Explanation

  Correct Answer: (b) 1 and 2

  • Ultrasonic waves are sound waves with frequencies above 20,000 Hz. They are safer than X-rays for imaging internal organs because they do not ionize tissues, reducing the risk of harm.
• 8

  Which of the following has the least penetrating power ?

   

  • A

    (a) Alpha particles 

     

  • B

    (b) Beta particles

     

  • C

    (c) Gamma rays

     

  • D

    (d) All have the same penetrating power

  Explanation

  Correct Answer: (a) Alpha particles

  • Alpha particles have the least penetrating power due to their large mass and charge, which cause them to lose energy quickly as they interact with matter.
• 9

  Optic fibres are mainly used for which of the following ?

   

  • A

    (a) Communication 

     

  • B

    (b) Weaving

     

  • C

    (c) Musical instruments

     

  • D

    (d) Food industry

  Explanation

  Correct Answer: (a) Communication

  • Optical fibers are widely used in communication for transmitting data as light signals. Their high speed and low signal loss make them essential in modern telecommunications.
• 10

  Which of the following are most penetrating?

   

   

  • A

    (a) α-rays         

     

  • B

    (b) β-rays 

     

  • C

    (c) γ-rays         

     

  • D

    (d) X-rays

  Explanation

  Correct Answer: (c) Gamma rays

  • Gamma rays are highly penetrating electromagnetic waves. They have no mass or charge, allowing them to pass through most materials more effectively than other types of radiation, such as alpha or beta particles.