Pre Boards

Practice to excel and get familiar with the paper pattern and the type of questions. Check you answers with answer keys provided.

Sample Papers

Download the PDF Sample Papers Free for off line practice and view the Solutions online.

ISC Class 12 Physics Solved Question Paper 2016

Long Answer Type

31.

a) 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.

32.
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) Given:

Wavelength, $straight lambda space equals space 198 space nm space equals space 198 space straight x space 10 to the power of negative 9 end exponent straight m$
Work function, W = 2.5 eV = 2.5 x 1.6 x 10^-19 J

Using the formula,

$straight E subscript straight k space equals space hc over straight lambda minus straight W eV subscript straight o space equals space hc over straight lambda minus straight W straight V subscript straight o space equals space hc over eλ minus straight W over straight e equals space fraction numerator 6.6 space straight x space 10 to the power of negative 34 end exponent straight x 3 straight x 10 to the power of 8 over denominator 1.6 space straight x space 10 to the power of negative 19 end exponent straight x 198 straight x 10 to the power of negative 19 end exponent end fraction space minus space fraction numerator 2.5 straight x 1.6 straight x 10 to the power of negative 19 end exponent over denominator 1.6 straight x 10 to the power of negative 19 end exponent end fraction equals space fraction numerator 6.6 space straight x space 3 space straight x space 10 to the power of negative 26 end exponent straight x 10 to the power of 28 over denominator 1.6 space straight x space 198 end fraction minus 2.5 equals space fraction numerator 19.8 space straight x space 10 squared over denominator 1.6 straight x 198 end fraction minus 2.5 equals 0.0625 space straight x 10 squared minus 2.5 equals space 6.25 space minus space 2.5 equals 3.75 space straight V$

b)

i) De-Broglie Hypothesis: Whenever a material particle like electron, proton etc., is in motion, then it behaves as a wave. That is, the material particles in motion are associated with a wave. These waves are called as matter waves or de-broglie waves. The wavelength of the matter waves is called 'de-broglie wavelength',

$straight lambda space equals space straight h over mv$

ii) Conclusion and Davison and Germer's Experiment: Energy of the incident beam of electrons can be varied by changing the applied voltage to the elctron gun.

33.

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.

34.

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.

35.

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.