Home
Class 12
PHYSICS
Answer the following : (a) Name the em...

Answer the following :
(a) Name the em waves which are suitable for radar system used in aircraft navigation. Write the range of frequencey of these waves.
(b) If the earth did not have atmosphere, would its average surface temperature be higher or lower than what it is now? Explain

Text Solution

Verified by Experts

(a) Microwaves are suitable for radar systems used in aircraft navigation. The range of frequency for these waves is 109Hz to 1012Hz.
(b) In the absence of atmosphere, there would be no greenhouse effect on the surface of the Earth. As a result, the temperature of the Earth would decrease rapidly, making it difficult for human survival.
(c) An em wave carries a linear momentum with it. The linear momentum carried by a protion of wave having energy U is given by p = Uc.
Thus, if the wave incident on a material surface is completely absorbed, it delivers energy U and momentum p = Uc to the surface.
If the wave is totally reflected, the momentum delivered is p = 2Uc because the momentum of the wave changes from p to -p . Therefore, if follows that an em waves incident on a surface exert a force and hence a pressure on the surface.
Promotional Banner

Topper's Solved these Questions

  • XII BOARDS

    XII BOARD PREVIOUS YEAR PAPER ENGLISH|Exercise [SET - II DELHI BOARD]|5 Videos

  • XII BOARDS

    XII BOARD PREVIOUS YEAR PAPER ENGLISH|Exercise [SET - III, DELHI BOARD]|6 Videos

  • XII BOARDS

    XII BOARD PREVIOUS YEAR PAPER ENGLISH|Exercise SET-II|33 Videos

  • SAMPLE PAPER 2019

    XII BOARD PREVIOUS YEAR PAPER ENGLISH|Exercise SECTION D|6 Videos

Similar Questions

Explore conceptually related problems

A : If the earth did not have an atmosphere, its average surface temperature would have been lower. R : In the absence of atmosphere, the green house effect will be absent.

Asnwer the following : (a) Name the em waves which are used for the treatment of certain forms of cancer. Write their frequency range. (b) Thin ozone layer on top of stratosphere is crucial for human survival. Why ? (c) Why is the amount of the momentum transferred by the em waves incident on the surface so small?

Assertion : If earth did not have atmosphere, its average surface temperature would be lower than what it is now Reason : Green house effect of the atmosphere would be absent, if earth did not have atomosphere.

Assertion:- If earth did not have atomosphere, its average surface temperature would be lower than what it is now. Reason:- Greenhouse effect of the atmosphre would be absent, if earth did not have atmosphere.

(a) Where should an object be kept on the principal axis of a convex lens of focal length 20 cm in order to get an image, which is double the size of the object? (b) Name the part of the electromagnetic spectrum which is (i) Suitable for radar systems used in aircraft navigation. (ii) Produced by bombarding a metal target with high electrons.

(b) Write the Lens Maker's formula and use it to obtain the range of mu (The refractive index of the material of the lens) for which the focal length of and equiconvex lens, kept in air, would have a greater magnitude than that of the radius of curvature of its two surfaces.

Answer the following: (a) What is a wave front? How does it propagate? Using Huygens' principle, explain reflection of a plane wavefront from a surface and verify the laws of reflection. (b) A parallel beam of light of wavelength 500 nm falls on a narrow slit and the resulting diffraction pattern is obtained on a screen 1 m away. If the first minimum is formed at a distance of 2.5 mm from the centre of screen, find the (i) width of the slit, and (ii) distance of first secondary maximum from the centre of the screen.

Given below is the diagram of a human ovum surrounded by a few sperms. Study the diagram and answer the following questions : (a) Which one of the sperms would reach the ovum earlier ? (b) Identify 'D' and 'E'. Mention the role of 'E'. (c ) Mention what helps the entry of sperm into the ovum and write the changes occuring in the ovum during the process. (d) Name the specific region in the female reproductive system where the event represented in the diagram takes place.

Consider a spacecraft in an elliptical orbit around the earth At the lowest point or perigee of its orbit it is 300km above the earth's surface at the highest point or apogee it is 3000km above the earth surface (a) What is the period of the spacecraft's orbit (b) using conservation of angular momentum find the ratio of spacecraft's speed at perigee to its speed at apogee (c) Using conservation of energy find the speed at perigee and the speed at apogee (d) it is derised to have the spacecraft escape from the earth completrly if the spacecraft's rockets are fired at perigee by how much would the speed have to be increased to achieve this? What if the rockets were fired at apogee Which point in the orbit is the most efficient to use ?

A system of greater disorder of molecules is more probable. The disorder of molecules is reflected by the entropy of the system.A liquid vapourises to form a more disordered gas.When a solute is present, there is additional contribution to the entropy of the liquid due to increased randomness.As the entropy of solution is higher than that of pure liquid, there is weaker tendency to form the gas.Thus, a solute (non-volatile) lowers the vapour pressure of a liquid, and hence a higher boiling point of the solution. Similarly, the greater randomness of the solution opposes the tendency to freeze.In consequence, a lower the temperature must be reached for achieving the equilibrium between the solid (frozen solvent) and the solution.Elevation of B.Pt.(DeltaT_b) and depression of F.Pt.(DeltaT_f) of a solution are the colligative properties which depend only on the concentration of particles of the solute, not their identify.For dilute solutions. DeltaT_b and DeltaT_f are proportional to the molality of the solute in the solution. DeltaT_b=K_bm , K_b =Ebullioscopic constant= (RT_(b)^(@^(2))M)/(1000 DeltaH_(vap)) And DeltaT_f=K_fm , K_f =Cryoscopic constant= (RT_(f)^(@^(2))M)/(1000 DeltaH_(fus)) (M=molecular mass of the sovent) The values of K_b and K_f do depend on the properties of the solvent.For liquids, (DeltaH_(vap))/T_b^@ is almost constant. [Troutan's Rule, this constant for most of the unassociated liquids (not having any strong bonding like Hydrogen bonding in the liquid state ) is equal to 90 J//"mol" .] For solutes undergoing changes of molecular state is solution (ionization or association), the observed DeltaT values differ from the calculated ones using the above relations In such situations, the relationships are modified as DeltaT_b=i K_bm, DeltaT_f=i K_fm where i=Van't Hoff factor, greater than unity for ionization and smaller than unity for association of the solute molecules. A mixture of two Immiscible liquids at a constant pressure of 1 atm boils at a temperature

XII BOARD PREVIOUS YEAR PAPER ENGLISH-XII BOARDS-[SET - I]
  1. Given a uniform electric field vecE=5xx10^(3)hatiN//C, find the flux o...

    Text Solution

    |

  2. For a single slit of width ''a'' the first minimum of the interference...

    Text Solution

    |

  3. Write the truth table for the combination of the getes shown. Name the...

    Text Solution

    |

  4. Identify the logic gates marked P and Q in the circuit Fig. Write the ...

    Text Solution

    |

  5. A proton and deuteron are accelerated through the same accelerating po...

    Text Solution

    |

  6. (i) Mono chromatic light of frequency 6.0xx10^(14)Hz is produced by a ...

    Text Solution

    |

  7. A 12.5 eV electron beam is used to bombard gaseous hydrogen at room te...

    Text Solution

    |

  8. When Sunita, a class XII student, came to know that her parents are pl...

    Text Solution

    |

  9. A potentiometer wire of length 1 m has a resistance of 10Omega. It is ...

    Text Solution

    |

  10. (a) Draw a labelled ray diagram showing the formation of a final image...

    Text Solution

    |

  11. (a) A mobile phone lies along the principal axis of a concave mirror. ...

    Text Solution

    |

  12. Derive an expression for the magnetic moment (vec mu) of an electron r...

    Text Solution

    |

  13. (a) State Ampere's circuital law, expressing it in the integral form. ...

    Text Solution

    |

  14. Answer the following : (a) Name the em waves which are suitable for ...

    Text Solution

    |

  15. Deduce the expression, N=N(0)^(-lambdat) for the law of radioactive de...

    Text Solution

    |

  16. (a) How does one demonstrate, using a suitable diagram, that unpolaris...

    Text Solution

    |

  17. (a) Describe a simple experiment (or activity) to show that the polari...

    Text Solution

    |

  18. Draw a schematic sketch of an generator describing its basic elements....

    Text Solution

    |

  19. Using the necessary circuit diagram, show how the V-I characteristics ...

    Text Solution

    |

  20. (a) Differentiate between three segments of a transistor on the basis ...

    Text Solution

    |