Physics Paper-i I

FEDERAL PUBLIC SERVICE COMMISSION COMPETITIVE EXAMINATION FOR RECRUITMENT TO POSTS IN B.P.S.17 UNDER THE FEDERAL GOVERNMENT, 2000. PHYSICS PAPER-I I TIME ALLOWED 3 HOURS MAXIMUM MARKS : 100 NOTE: Attempt FIVE questions in all, including question No.8 which is COMPULSORY. All questions carry equal marks. Q.1. (a) A dielectric sphere is placed in a uniform electric field. Draw a neat diagram showing a distortion produced in the field. Calculate, electric field outside and inside the dielectric sphere. (10) (b) Explain the dielectric polarization. Establish a relation between electric field strength E, polarization P and electric induction D. (10) Q.2 (a) Give a brief account of the phenomenon of electromagnetic induction. Describe two experiments to demonstrate it. (10) (b) Prove a relation between the induced e.m.f. and. the rate of change of lines of magnetic force through a circuit (10) Q.3. (a) What is transistor biasing? How will you connect a PNP transistor in i) common base and ii) common emitter configurations. Draw their characteristics curves and discuss their current gain, voltage gain and input impedance. Give the applications of two configurations. (12) (b) Deduce the conditions under which the discharge of a condenser is Oscillatory in character. Find an expression for the frequency of oscillations. (8) Q.4. (a) Outline the basic facts of Photo electricity. Give the law of Photoelectric emission. How can they be explained? (12) (b) The kinetic Energies of photoelectrons range from zero to 4.0x1019J, when light of wavelength 3000 A° falls on a surface, what is the stopping potential for this light? What is the threshold wavelength for the material? (8) (1 eV= 1.602x1O19J.) Q.5. (a) State fundamental postulates of Bohr’s Theory of hydrogen atom Derive the mathematical expression for energy of electron in hydrogen atom. Give the interpretation of negative sign. (12) (b) Give an account of different series of Spectral lines of hydrogen atom. (8) Q.6. (a) Give the significance of Schrodinger’s Wave equation in wave mechanics. Apply it to calculate energies of particle in a box and discuss the results. (12) (b) What is Ileisenberg’s Uncertainty principle? Explain its importance in the development of physics. (8) Q.7. Write a short essay on any two of the following: (20) (a) Nuclear Reactors and their classifications

(b) Mass Spectrometer and Isotope detection (c) AM Radio Receivers and Transmitters Q. 8. Write only the correct answer in the answer book. Don’t reproduce the questions: (20) (i) The neutrino does not possess (a) charge. (b) linear momentum. (c) angular momentum. (d) energy. (ii) The particle whose properties are most nearly the same as those of the proton is the (a) positron. (b) neutron. (c) antiproton. (d) positive pion. (e) none of these (iii) The element whose nuclei contain the most tightly bound nucleons is (a) helium. (b) carbon. (c) iron. (d) uranium. (e) none of these (iv) As a sample of a radioactive nuclide decays, its half—life (a) decreases. (b) remains the same. (c) increases. (d) any of the above, depending on the nuclide. (v) Current in an n-type semiconductor is carried by (a) electrons. (b) holes. (c) positive ions. (d) electrolytes. (e) none of these (vi) Pauli’s exclusion principle states that no two electrons in an atom can (a) be present in the same probability cloud. (b) have the same spin. (c) have, the same quantum numbers. (d) interact with each other. (e) none of these (vii) The number of possible orientations of an atomic electron in a magnetic field is * (a) 1. (b) 2. (c) 4. (d) 2p . (e) none of these (viii) A hydrogen atom is in its ground state when its orbital electron (a) is within the nucleus. (b) has escaped from the atom. (c) is in its lowest energy level. (d) is stationary. (e) none of these (ix) Electromagnetic waves transport (a) wavelength. (b) frequency. (c) charge. (d) energy. (e) all of these (x) The reactance of a capacitor is proportional to (a) Ö f. (b) f. (c) f2. (d) 1/f. (e) none of these (xi) The capacitive reactance of a 5-m F capacitor in a 20-kHz circuit is

(a) 0.63W . (b) 1.6W . (c) 5W . (d) 16W . (e) none of these (xii) The impedance of a circuit does not depend on (a) I (b) f. (c) R. (d) C. (e) all of these (xiii) At resonance, itis not true that (a) R=Z (b) XL=1/XC (c) P=IV (d) I=V/R (xiv) A voltmeter across an AC circuit reads 50 V and an ammeter in series with the circuit reads 5 A. The power consumption of the circuit (a) is less than or equal to 250 W. (b) is exactly equal to 250 W. (c) is equal to or more than 250 W. (d) may be less than, equal to, or more than 250 W. (e) none of these (xv) The magnetic flux through a wire loop in a magnetic field B does not depend on (a) the area of the loop. (b) the shape of the loop. (c) the angle between the plane of the loop and the direction of B. (d) the magnitude B of the field. (e) none of these (xvi) The alternating current in the secondary coil of a transformer is induced by (a) a varying electric field. (b) a varying magnetic field. (c) the iron core of the transformer. (d) motion of the primary coil. (a) none of these (xvii) When a diamagnetic substance is inserted in a current carrying solenoid, the magnetic field is (a) slightly decreased. (b) greatly decreased. (c) slightly increased. (d) greatly increased. (e) none of these (xviii) The N-type semiconductor is electrically (a.) negative (b) positive (c) neutral (d) charged (xix) When a 100¾ W, 240-V light bulb is operated at 200 V, the current that flows in it is (a) 0.35 A (b) 0.42 A (c) 0.50 A (d) 0.58 A (e) none of these (xx) The a of a transistor is (a) current gain in common base (b) current gain in common emitter (c) voltage gain in common emitter (d) voltage gain in common base (e) none of these *************************************