[OBJECTIVE]
Subject: Concepts of Modern Physics
Time Allowed: 10 Minutes
Maximum Marks: 10
NOTE: Attempt this Paper on this Question Sheet only. Please encircle the correct option. Division of marks is given in front of each question. This Paper will be collected back after expiry of time limit mentioned above.
Part-I Encircle the right answer, cutting and overwriting is not allowed. (10)
1. The maximum kinetic energy of photo electrons depends upon a
a) Intensity b) Frequency
(c) Temperature d) All these
2. The spectrum of black body radiation is
a) Line Spectrum b) Continuous spectrum
c) Band spectrum d) Discrete
3. If the particles listed all have the same KE, which has the longest wavelength
a) Neutron b) Electron
c) Proton d) Alpha particle
4. Rayleigh-Jean’s law holds good for which of the following?
a) Short wavelength b) Intermediate wavelength
c) Both for short & long wavelength d) Long wavelength
5. What is the minimum possible momentum of particle, trapped in an infinite one dimensional potential well of width L
a) 0 b) h2/2L
c) h2/2L2 d) h/2L
6. According to Moseley’ the square root of the frequencies of lines in x-ray spectra depends linearly on
a) Mass number b) Atomic number
c) Quantum number d) None of these
7. The current due to motion of majority charge carrier is called
a) Diffusion current b) Conventional current
c) Leakage current d) Drift Current
8. At critical temperature, the resistivity of the superconductors fall to zero
a) Gradually b) Exponentially
c) Suddenly d) None of above
9. In Beta decay, the kinetic energy spectrum of the emitted electrons is
a) Discrete b) Continuous
c) Band spectrum d) line spectrum
10. The unit of activity of a radioactive source is
a) rad b) Curie
c) Sievert d) Roentgen
[SUBJECTIVE]
Subject: Concepts of Modern Physics
Time Allowed: 2 Hours 45 Minutes
Maximum Marks: 50
NOTE: ATTEMPT THIS (SUBJECTIVE) ON THE SEPARATE ANSWER SHEET PROVIDED.
Part-II Give short answers, each answer carries equal marks. (20)
Q#1: Explain, why an evacuated tube is used to examine photoelectric emission
Q#2: Briefly describe Einstein’s Photoelectric equation.
Q#3: Briefly comment on energy-time uncertainty relationship.
Q#4: Why is the Heisenberg uncertainty principle not more radially apparent in our daily observations?
Q#5: Explain briefly the difference between conduction band and valance band.
Q#6: What is difference between spontaneous emission and stimulated emission?
Q#7: State Bohr’s postulates of the hydrogen atom.
Q#8: Explain the difference between donor and accepter impurities?
Q#9: What is metastable state? what roll such a state play in laser operation?
Q#10: What is doping. How N type semiconductor is formed by doping.
Part-III Give detailed answers, Each answer carries equal marks. (30)
Q#3: Define Compton Effect. In a single photon-electron collision, show that Compton shift depends on scattering angle of photon.
Q#4: (a) Derive the expression for the energy of an electron, trapped inside an infinitely deep potential well of width L.
(b) When an electron is confined to an infinite deep potential well of width 100 pm, what will be the energy of its lowest allowed state?
Q5: (a) Explain the Rutherford’s gold foil experiment for discovering the atomic nucleus.
(b) Calculate the binding energy of deuteron. The needed atomic masses are mn= 1.008665, m(1H) = 1.007825 u, m(2H)= 2.014102 u.
[OBJECTIVE]
Subject: Physics-IV (Concepts of Modern Physics)
Time Allowed: 10 Minutes
Maximum Marks: 10
NOTE: Attempt this Paper on this Question Sheet only. Please encircle the correct option. Division of marks is given in front of each question. This Paper will be collected back after expiry of time limit mentioned above.
Part-I Encircle the correct option, cutting and overwriting is not allowed. (10)
1. When a photo-emissive surface is exposed to light of some suitable fre quency:
(a) Protons are emitted (b) Photons are emitted
(c) Photoelectrons are emitted (d) Photograph can be takon
2. Quasi-free electrons means:
(a) Loosely bound electron (b) Tightly bound electron
(c) Any of these (d) Completely free electron
3. Compton shift refers to:
(a) Proton (b) Meson
(c) Positron (d) Photon
4. The part/s of a photocell is/are:
(a) Thin anode rod (b) Evacuated glass tube
(c) Evacuated glass tube’aid Cathode of an appropriate metal surface
(d) Cathode of an appropriate metal surface
5. Time:
(a) is relative (b) is an absolute quantity
(c) Depends upon motion of frame of reference (d) All above
6. The special theory of relativity is based on:
(a) Two postulates (b) Four postulates
(c) Three postulates (d) One postulate
7. Photoelectrons are emitted when visible light falls on:
(a) Potassium (b) Sodium and Potassium
(c) Cesium coated oxidized silver (d) Sodium
8. There is no way to detect:
(a) Absolute uniform motion (b) State of rest
(c) State of motion (d) Accelerated motion
9. The concept of direction is purely:
(a) Absolute (b) Relative to stars always
(c) Relative (d) Relative to the sun always
10. All motions are:
(a) Absolute (b) Relative to the instrument
{c) Relative to a person and Relative to the instrument (d) Relative to a person
[SUBJECTIVE]
Subject: Physics-IV (Concepts of Modern Physics)
Time Allowed: 2 Hours 45 Minutes
Maximum Marks: 50
NOTE: ATTEMPT THIS (SUBJECTIVA) ON THE SEPARATE ANSWER SHEET PROVIDED.
Part-II Give short details of each of them, each answer carries equal marks. (20)
Q#1: What is blackbody radiation? Write down Rayleigh’s law and Planck’s law for energy density and explain the difference between them. What is ultraviolet catastrophe?
Q#2: The kinetic energies of photoelectrons range from zero to 4.0 x 10-19J when light of wavelength 3000A falls on a surface. What is the stopping potential for this light?
Q#3: Determine the maximum scattering angle in a Compton experiment for which the scattered photon can produce a positron-electron pair.
Q#4: Calculate the kinetic energy of a neutron’ whose de Broglie wavelength is 0.7A.
Part-III Give brief answers, each answer carries equal marks. (30)
Q#1: (a) Find the energies of two photons that are produced when annihilation occurs between an electron and positron that are initially at rest.
(b) Determine a photon’s threshold energy for pair production.
Q#2: Discuss in detail the stability of nuclei.
Q#3: State and explain de Broglie hypothesis. State properties of matter waves.
