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# Physics, Paper-II (CSS Paper 2015) FEDERAL PUBLIC SERVICE COMMISSION
COMPETITIVE EXAMINATION FOR RECRUITMENT TO POSTS
IN BS-17, UNDER THE FEDERAL GOVERNMENT, 2015
PHYSICS, PAPER-II

TIME ALLOWED: THREE HOURS (PART-I MCQs) Maximum Marks: 20
PART –I (MCQs) Maximum 30 Minutes (PART-II) Maximum Marks: 80

Note: (i) Part-II is to be attempted on the separate Answer Book.
(ii) Attempt ONLY FOUR questions from PART-II. All questions carry EQUAL Marks.
(iii) All the parts (if any) of each Question must be attempted at One Place instead of at different places.
(iv) Candidate must write Q. No. in the Answer Book in accordance with Q. No. in the Q. Paper.
(v) No Page /Space be left blank between the answers. All the blank pages of Answer Book must be crossed.
(vi) Extra attempt of any question or any part of the attempted question will not be considered.

PART-II

Q. 2. (a) State and prove Gauss’s law of electrostatics. Derive its differential form.
(b) Use Gauss’s lave to calculate the electric field due to a line charge.
(c) A point charge of µC is at the centre of j cubic A Gaussian surface 55 cm on edge. What is the net electric flux through this surface? Use
Q.3. (a) Analyze the RLC, -series circuit using j-operator method and discuss its frequency response. Discuss the importance of this circuit.
(b) Find the impedance of a circuit consisting of a resistor, 5.0µF capacitor and 50mH inductor in series at a frequency of 10 kHz.
(c) What are the advantages of A.C. mains supply?
Q.4. (a) Describe the f6rnjrd and reverse biascd of a PN junction.
(b) Explain the nothing of a bridge rectifier using a neat and labeled circuit diagram.
(c) Why semiconductor devices are preferred over the vacuum tubes?
Q.5. (a) What is meant by Compton Effect? Derive an expression for Compton shift in wavelength.
(b) A beam of X-rays is scattered by a carbon target. At 45o from the beam direction the scattered X-rays have a wavelength of 2.2pm. What is the wavelength of the X-rays in the direct beam?

Q.6. (a) Derive expressions for half-life and mean life of a radioactive substance.
(b) The activity of a certain radionuclide decreases to 15 percent of the original value in 10days. Find its half-life.
(c) Give any two industrial or medical uses of radioisotopes.
Q.7. (a) Differentiate between nuclear fission and fusion.
(b) Draw a labeled diagram of a nuclear reactor and explain the functions of various parts.
(c) Calculate the energy released in the following fission reaction induced by slow neutrons.