Here physics classes by Nayan jha providing the test paper based on the chapter Dual nature, Atoms nuclei and semiconductor devices , After solving this question paper students can notice his preparation for class 12th CBSE (Board examination ).

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PHYSICS CLASSES BY NAYAN JHA

Test class 12th

( Dual nature, Atoms and Nuclei and Semiconductor)

Sec-A ( each questions carry 2 marks)

1.Define the term threshold frequency and stopping potential in relation to the

phenomenon of photoelectric effect . how is photoelectric current affected on increasing

the (I) frequency (II) intensity of the incident radiations and why?

- Draw the graph showing the variation of potential energy between a pair of nucleons as a

function of their separation. Indicate the regions in which the nuclear forces is (i) attractive,

(ii) repulsive. Write two important conclusions which you can draw regarding the nature of

the nuclear forces. - Distinguish between conductors, insulator and semiconductors on the basis of their

energy bands.

Or,

State the reasons, why GaAs is most commonly used in making a solar cell.

Sec-B (each questions carry 3 marks ) - An electron of mass m and charge q is accelerated from rest through a potential

difference V , obtain the expression for the de-Broglie wavelength associated with it . if electron and proton are moving with the same K.E. , which one of them will have a large De-Broglie wavelength associated with it ? give reason . - State any two postulates of Bohr theory of hydrogen atom . what is the maximum

possible no. of spectral lines observed when the hydrogen atom is in its second exited state? justify your answer . calculate the ratio of the max. and min. wavelength of the radiation

emitted in this process. - Using Bohr postulates for hydrogen atom , show that the total energy of the electron in

the stationary states can be expressed as the sum of kinetic energy(K) and potential energy

(U) , where K=-2U. hence , deduce the expression for the total energy in the nth energy level

of hydrogen atom . - Draw the binding energy per nucleon curve . using the curve state clearly how the release

in energy in the process of nuclear fission and nuclear fusion can be explained. - The energy level diagram of an element is given below . identify using necessary

calculations , which transition corresponds to the emission of the spectral line of

wavelength 102.7 nm . which transition corresponds to the emission of radiation of

maximum wavelength?

. - (i)Define the activity of the radioactive material and write its SI unit. plot a graph showing

the variation of activity with respect to time of a given radioactive sample.(ii) what is meant

by half life time of a radioactive element ? the half life of a radioactive sample is 30s

calculate (a) the decay constant and (b)time taken for the sample to decay by 3/4thof the initial value . - Explain, with the help of a circuit diagrams, the working of a photo-diode. Write briefly

how it is used to detect the optical signals.

Or

a) How is photodiode fabricated

b) Briefly explain its working. Draw its V-I characteristic for two different intensities of

illumination.

Sec –c ( case study based questions) - Line spectra of the hydrogen atom –The spectral series of hydrogen atom were accounted for

by the Bohr using the relation 1/ʎ = R(1/n1-1/n2). Where R is the Rydberg constant . Lyman series is obtained when an electron jumps to first orbit from any subsequent orbit . Similarly Balmer

series is obtained when an electron is jumps to 2nd orbit from any subsequent orbit . , Paschen series is obtained when an electron is jumps to 3rd orbit from any subsequent orbit. Whereas

Lyman series is lies in U.V. region , Balmer series in visible region and Paschen in infrared region.

Series limit is obtained when n2=infinity.

1.The wavelength of first spectral line of Lyman series is.(a) 1215.4 A (b)1215.3cm (c)1215.4m

(d)1215.4mm.

(ii)The wavelength limit of Lyman series is (a)1215.4 A (b)511.9A (c)951.6A (d)911.6A

(iii) The frequency of spectral line of Balmer series is (a) 1.097 x 107 Hz (b) 4.57x1014A (c) 4.57 x

1015Hz (d)4.567 x 1016Hz

(iv)Which of the following transition in hydrogen atoms emits photons of highest frequency (a)

n=1 to n=2 (b) n=2 to n=6 (c) n=6 to n=2 (d)n=2 to n=1 .

(v) The ratio of minimum to max wavelength in Balmer series is (a) 5:9 (b) 5:36 (c) 1:4 (d)3:4 .