Physics_2009_S3_Del_QP_Sol

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					2/3/2011                                           Subjective Test Paper - Physics - Meritn…




  Physics 2009 Set 3                                                                             Close


 Subjective Test




     These are additional set 3 questions.



    Question 2 ( 1.0 marks)
   At what angle of incidence should a light beam strike a glass slab of refractive index     , such that
   the reflected and the refracted rays are perpendicular to each other?

   Solution:
   When angle between reflected and refracted ray is 90°,




    Question 3 ( 1.0 marks)
   What is space wave propagation?

   Solution:
   Space wave propagation is another mode of radio wave propagation. It travels in a straight line from
   transmitting antenna to the receiving antenna.

   Space wave propagation is used for line of sight communication and satellite communication.



    Question 5 ( 1.0 marks)
   Name the part of electromagnetic spectrum which is suitable for

   (i) radar systems used in aircraft navigation

   (ii) treatment of cancer tumours

   Solution:
   (i) Microwaves are used in radar systems.

   (ii) Gamma rays are used in treatment of cancer tumours.



    Question 6 ( 1.0 marks)
   Two nuclei have mass numbers in the ratio 2: 5. W hat is the ratio of their nuclear densities?

   Solution:
   Nuclear density is independent of mass number and is the same for every nucleus. Thus, the ratio of
   their nuclei is 1: 1.



    Question 19 ( 3.0 marks)
   State Gauss’ law in electrostatics. Use this law to derive an expression for the electric field due to an
   infinitely long straight wire of linear charge density λ Cm−1 .


   Solution:
meritnation.com/…/PPE7T6TB$mi0o7w…                                                                             1/3
2/3/2011                                          Subjective Test Paper - Physics - Meritn…
    Solution:

   According to Gauss’s law, the electric flux through a closed surface is         the charge q enclosed

   by the surface.




   A Gaussian surface, which is cylindrical in shape, is drawn whose axis is the same as the axis of the
   straight wire.

   The symmetry argument implies that electric field has the same magnitudes over the whole curved
   surface area of the Gaussian surface. Furthermore, its direction must either be radially outward or
   radially inward depending upon polarity of the line charge.

   Let the electric field be   .

   Flux through the Gaussian surface

   = E × Area of the curved surface

   = E (2πrl)

   According to Gauss’s law,




    Question 23 ( 3.0 marks)
   Two parallel plate capacitors, X and Y, have the same area of plates and same separation between
   them. X has air between the plates while Y contains a dielectric medium of ∈ r = 4.




   (i) Calculate capacitance of each capacitor if equivalent capacitance of the combination is 4 µF.

   (ii) Calculate the potential difference between the plates of X and Y.

   (iii) What is the ratio of electrostatic energy stored in X and Y?

   Solution:
   Let the capacitance of X be C.

   The capacitance of Y will be




   (i)




   Capacitance of X = C = 5 µF

   Capacitance of Y = 4C = 20 µF
meritnation.com/…/PPE7T6TB$mi0o7w…                                                                         2/3
2/3/2011                                         Subjective Test Paper - Physics - Meritn…
   Capacitance of Y = 4C = 20 µF

   (ii) Charge on each capacitor, Q = CV

   Q = 4 µF × 12 V

   = 48 × 10 −6 C

   = 48 µC




   Potential difference across X is 9.6 V.

   Potential difference across Y is 2.4 V.


   (iii) Energy stored in X is           .



   Energy stored in Y is            .




   The ratio of electrostatic energy stored in X and Y is 4: 1.




meritnation.com/…/PPE7T6TB$mi0o7w…                                                           3/3

				
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