Class IX,Science,Date 21 Dec.2015

     1.       Why is it not possible to see an atom with naked eyes?                               (Page No.34)
           Answer:
           The dimension of atoms is very small of the order of 1 nm. More than a million atoms when staked one         over the other will make a layer that is barely as thick as a sheet of paper. Thus, we cannot see an atom with naked eyes.

       2.       Write down the formulae of                                                                           (Page No.39)
      (i) sodium oxide
      (ii) aluminium chloride
             (iii) sodium suphide
      (iv) magnesium hydroxide
             Answer:
            (i) Na₂O
            (ii) AlCl₃
            (iii) Na₂S
            (iv) Mg(OH)₂

     3.       What is immunization?                                                                            (Page No.187)
            Answer
                       Immunizationis defined as protection of the body from communicable diseases by administration 

                       of some  agent that mimics the microbe.

      4.       __________ virus is spread by the bite of infected  dog and ______animals.(Page No.187)

   Answer:  Rabies, others

      5.       Define 1watt of Power?

     Answer:

              When one joule work is done in one second by any agent, then its power is called to be one watt,

               It is the unit of Power.

      6.       According to the law of conservation of energy, energy can only be transformed from one

            form to another, It neither __________ nor ____________,it always remains the ________.

     Answer.  Created, destroyed, constant.                                                          (Page No.157)

      7.       Define Potential energy?                                                                          (Page No.153)

     Answer: The energy stored in a body or a system due to its position in a force field or due to its state 

                   of strain or configuration is called potential energy.

     8.       State any two conditions essential for being free of disease.                 (Page No.178)
    Answer
                    Two conditions essential for being disease-free are:
                    → Person should take balance diet.
                    → Personal and community hygiene.