Question Discussion & Solution

The logic followed here is:

'Thermometer' is used to measure 'temperatures'.

Similarly,

An 'anemometer' is a device used for measuring 'Wind' speed.

CONCEPT:

• Ultrasonic waves are the sound waves with frequencies higher than the upper audible limit of human hearing.
  • They have a short wavelength.
• Echo: If we shout or clap near a suitable reflecting object such as a tall building or a mountain, we will hear the same sound again a little later. This sound which we hear is called an echo.
  • Echoes are heard due to the phenomenon of Reflection of sound waves.
• SONAR: It a technique that uses sound propagation (usually underwater, as in submarine navigation) to navigate, communicate with or detect objects on or under the surface of the water
  • SONAR stands for ‘Sound Navigation and Ranging.’
  • SONAR is based on the principle of echo.
  • Sonar is often used as a measurement of acoustic location and echo characteristics of the target object in the water.
  • It sends ultrasonic waves towards the bottom area of the sea and after reflection, the sound comes to the ship. We measure the time taken by the sound wave and then we get the depth. 

EXPLANATION:​

• From the above discussion, we can say that the SONAR uses the principle of reflection of sound waves(Echo) to detect and locate objects. So option 2 is correct.
• Reverberation: The persistence of sound in a closed enclosure, due to continuous reflections at the walls or the floor or the ceiling of the enclosure, even after the source has stopped producing sound is known as 'reverberation'.

The correct option is, i.e. Brain.

• Hypothalamus-
  • The Hypothalamus is a part of Brain that plays a crucial role in many important functions of the Human Body.
  • The hypothalamus is located below the thalamus in the brain.
  • The hormones from the hypothalamus govern physiological functions such as temperature regulation, thirst, hunger, sleep, mood, and the release of other hormones within the body.
  • Hypothalamus regulates the pituitary gland.

The correct answer is F11.

• The F11 key can take our screen into and out of full-screen mode quickly and easily. 

​Important Points

• Function key
  • A function key is a key on a computer or terminal keyboard which can be programmed so as to cause an operating system command interpreter to perform certain actions, a form of a soft key.

​ 

• F11​
  • The Most simple use is the F11 key can take our screen into and out of full-screen mode quickly and easily. 
  • F11 key can be used by combined with Shift, Ctrl, Alt keys.
    • Some of the uses of the F11 key in MS Word.
      • SHIFT + F11 = Go to the previous field.
      • CTRL + F11 = Lock a field.
      • CTRL + SHIFT + F11 = Unlock a field.
      • ALT + F11 = Display Microsoft Visual Basic Code.
      • ALT + SHIFT + F11 = Display Microsoft Visual Studio Code.

​Additional Information

• F8
  • ​​We can access the menu by turning on your computer and pressing the F8 key before Windows starts.
• F9
  • F9 will refresh fields in Word and prompt Outlook to send and receive messages.
• F10
  • ​F10 activates the menu bar or Ribbon of an open application.
  • Shift + F10 is the same as right-clicking on a highlighted icon, file, or Internet link. 

Concept:

• Atoms are made up of subatomic particles - electrons protons and neutrons.
• In the center of an atom, a nucleus is present which contains protons and neutrons together known as nucleons.
• The mass of an atom is most concentrated at the center of the atom, i.e. the nucleus.

​Electrons:

• Discovered by Sir J.J Thomson in the year 1897.
• Previously named as cathode rays as they were supposed to be emitted from the cathode.
• They are deflected towards the positive side.
• They have high kinetic energy.
• They are deflected by an electric and magnetic field.
• It has a negative charge of

  \(charge=1.602\times10^{-19} coulombs \)
\(mass={1\over 1837}\times 9.107\times 10^{-28}g\)

Protons:

• Discovered by Goldstein.
• Depicted first as positive rays because it seemed to emerge from the anode.
• Mass of a proton is

 \(1.670 \times 10^{- 24}g\)

\(Charge=1.602\times 10^{-19} coulombs\)​

Explanation:

• Rutherford's discovery led to the discovery of nucleus.
• He found out that most of the mass of the nucleus is situated in its centre and contains the positively charged particles protons.
• The atom is otherwise empty and as electrons have negligible mass, the mass of an atom should be equal to the sum of mass of protons present in it.
• However, it was seen that in Helium, there are only two protons, so its mass should be twice the mass of each proton = \(2\times 1.008 a.m.u\).
• Experimental results revealed that it has a mass of 4.003a.m.u.
• Hence, it was concluded that the nucleus has particles containing no charge but mass almost equal to that of a proton.
• This was established by scientist James chadwick in 1932.

Additional Information

Rutherford's gold foil experiment: 

• He discovered the atomic nucleus and gave us an atomic model.
• He directed alpha particles towards a metal sheet.
• He saw that most of the alpha particles, which are positively charged particles, are not getting deflected.
• Most of the alpha particles emerged undeflected.

• Therefore, he concluded that most of the mass of the nucleus is situated in its centre and contains the positively charged particles protons.
• Electrons revolve around the nucleus in certain orbits.