physics 12th cbse

 Question1:

  A narrow slit is taken and a parallel beam of moving electrons is incident normally on it. At      a larger distance from the slit, a fluorescent screen is placed. Which of the following              statement is true if the size of the slit is further narrowed?

    ANS: The angular width of the central maxima of the diffraction pattern will increase

Question2:

  How does the diffraction band of blue light look in comparison with the red light?

   ANS: Diffraction pattern becomes narrower

Question3:

  Two coherent sources of light can be obtained from

   ANS: None of these

Question4:

  Which of the following phenomenon is not explained by Huygen’s wave theory?

   ANS: Photoelectric effect

Question5:

  What is the value of coherent time if L is the coherent length and c is the velocity of light?

   ANS: L/c

Question6:

  The colours on the soap bubble is due to

   ANS: Interference

Question7:

  In Young’s double-slit experiment, the phase difference between the light waves reaching      the third bright fringe from the central fringe will be (λ=6000 Å)

   ANS: 6π

Question8:

  Light propagates rectilinearly, due to

   ANS: wave nature

Question9:

  The refractive index of glass is 1.5 for light waves of X = 6000 A in vacuum. Its wavelength    in glass is

   ANS: 4000 Å

Question10:

  To observe diffraction, the size of the obstacle

  ANS: should be of the order of wavelength.