Long Answer Typea) A convex lens of focal length 5 cm is used as a simple microscope. Where should an object be placed so that the image formed by it lies at the least distance of distinct vision (D = 25 cm)?
b) Draw a labelled diagram showing the formation of an image by a refracting telescope when the final image lies t infinity.
a) Monochromatic light of wavelength 198 nm is incident on the surface of a metallic cathode whose work function is 2.5 eV. How much potential difference must be applied between the cathode and the anode of a photocell to just stop the photo current from flowing?
b) i) What is de-broglie hypothesis?
ii) What conclusion can be drawn from Davisson and Germer's experiment?
a) i) How are various lines of lyman series formed? Explain on the basis of Bohr's theory.
ii) Calculate the shortest wavelength of electromagnetic radiation present in Balmer series of hydrogen spectrum.
b) State the effect of the following changes on the X-rays emitted by Coolidge X-ray tube:
i) High voltage between cathode and anode is increased.
ii) Filament temperature is increased.
a) According to Bohr's theory, an electron migrates from one of its specific non-radiating orbits to another lower energy. When this happens, a photon is emitted having energy equal to the energy difference between the initial and final orbits.
The frequency of the emitted photon is given by,
where, Ei and Ef are the enrgies of the initial and final states and Ei > Ef.
Therefore, difference in energy between any two orbits is given by,
Using Planck's equation, 
In Lyman series, when an atom comes down from some higher energy level to the first energy level (lower energy level), i.e., n1 = 1and n2 = 2,3,4....). Then the emitted spectral lines are obtained in the ultraviolet region. The wavelength of these lines can be found by the following equation,
, n = 2,3,4,...
ii) Wavelength of the Balmer series,
, where, n= 3,4,5,....
For shortest wavelength,
Put n = 
in the above equation,
So,
where, r is the rydberg constant.
The value of R is 1.097 x 107 m-1
b) When high voltage is increased between the cathode and anode, then electrons emitting from filament, strike the target with a very high speed. Therefore, the penetrating power will increase.
ii) On increasing the filament temperature, the number of electrons striking the target per second increases and hence the number of X-ray photons emitted per second increases. Thus, the intensity of X-ray increases.
a) Half life of a certain radioactive material is 8 hours.
i) Find disintegration constant of this material.
ii) If one starts with 60 g of this substance, how much of it will disintegrate in one day?
b) Sketch a graph showing the variation of binding energy per nucleon of a nucleus with its mass number.
a) Draw a circuit diagram for the common emitter transistor amplifier. What is meant by phase reversal?
b) Write the truth table of the following circuit. Name the gate represented by this circuit.
Switch
