BACHELOR OF SCIENCE (B.Sc.) Term-End Examination December, 2016 PHYSICS PHE-07 : ELECTRIC AND MAGNETIC PHENOMENA

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1 No. of Printed Pages : 8 I PHE-07I BACHELOR OF SCIENCE (B.Sc.) Term-End Examination December, 2016 PHYSICS PHE-07 : ELECTRIC AND MAGNETIC PHENOMENA Time : 2 hours Maximum Marks : 50 Note : All questions are compulsory. Marks allotted for each question are indicated against it. You may use log tables or non-programmable calculators. Symbols have their usual meanings. The values of physical constants are given at the end. 1. Attempt any five parts : 5x4=20 (a) (b) Two point charges Q 1 and Q2 are 3 m apart and their combined charge is 20!AC. If one point charge repels the other with a force of N, what are the magnitudes of the two charges? The surface charge density of a flat sheet of area 50 cm2 is a. An electron situated at a distance of F5 cm from the centre of the sheet experiences a force of 1.8 x N directed away from the sheet. Calculate the total charge on the sheet. PH E-07 1 P.T.O.

2 (c) (d) (e) (f) (g) (h) Show that when a dielectric material is filled between the plates of a parallel plate capacitor, the value of capacitance increases by a factor K, the dielectric constant of the material. In a cyclotron, the diameter of the pole faces is 100 cm and the magnetic field between the pole faces is 0.60 tesla. The cyclotron is used for accelerating protons. Calculate the kinetic energy of protons in ev. In the Bohr model, the electron of a hydrogen atom moves in a circular orbit of radius 5.3 x m with a speed of 2.2 x 106 ms-1. Determine its frequency and current in the orbit. An electron of mass m moving around a nucleus in a circular path of radius r constitutes an atomic magnet. Obtain the relation between its magnetic moment and the angular momentum of the electron. Define self-inductance and obtain the expression for self-inductance of a solenoid. The electric field of an electromagnetic wave in vacuum is given by E. = 0, Ey = 30 cos (2rc x 10 8 t - (-2 ) rcx), E z = 0 3 where E is in volts per metre, t is in seconds and x is in metres. Determine the frequency, the wavelength, the direction of propagation and the direction of the magnetic field associated with the wave. PHE-07 2

3 2. Attempt any one part : (a) (b) ABCD is a square of side 0.02 m. Charges of 16 x 10-9 C, -16 x 10-9 C and 32 x 10-9 C are placed at points A, B and C, respectively. Determine the magnitude and direction of electric field at the point D. 10 Discuss the effect of electric field on a dielectric. Deduce Gauss's law for a dielectric medium Attempt any one part : (a) (b) State Biot-Savart's law. Using this law, derive an expression for magnetic field along the axis of a current loop. Write one analogy and one difference between Coulomb's law and Biot-Savart's law (i) A long straight wire of radius 5.0 mm carries a current of 20 A. Calculate the magnetic field at the surface of the wire. Calculate the perpendicular distance from the axis of the wire at which the magnitude of the magnetic field will be half of its value at the wire surface. 3+3 (ii) The value of the magnetic field at the centre of an air core solenoid is 0.40 mt. If the current flowing in the solenoid is 0.4 A, calculate the number of turns per cm. 4 PHE-07 3 P.T.O.

4 4. Attempt any one part : (a) (b) Define Lorentz force. A beam of electron passes undeflected through two mutually perpendicular electric and magnetic fields. If the electric field is cut off and the same magnetic field is maintained, the electrons move in the magnetic field in a circular path of radius 2.2 cm. Determine the ratio of the electronic charge to mass if the magnitude of electric field is 15 kvm-1 and the magnitude of magnetic field is 2 x 10-3 T. 3+7 Write Maxwell's equations in differential form for vacuum with no source of charges or currents and deduce the wave equation. Also calculate the speed of electromagnetic waves. 4+6 Physical Constants : Mass of electron = 9.1 x kg Mass of proton = 1.7 x kg Charge of electron = 1.6 x C 1 = 9 x 109 N m2 C-2 47t8 0 1.to = 47 x ie NA-2 E = 8.85 x F m-1 PHE-07 4

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6 (ii) kg If-A-R flilick IRlz * 41.q-i sm*-'1-1,4, TO IR ReII Alc11 14X/ft 'aft W T K T W4 Alai t, 71 K, smcveilct) TR* smcs)f;kch -PR* (Er) %I:ft ti crovi * d T c *r eel I ki 100 cm t wan- wo-*1 * Trrq 0.60 tesla I r kii*ctovi mica cr-a * NAl t I.T1 3ti i1 ev takchicio *tf* I (V) Q.T Hiso 4,.K1-017q TRITful 5.3 x m 1,3-041 ait ralerg 2.2 x 106 ms-1 TF Ikl-1C *till atrin3 mu Trrq AtTrita. *tr4r (q) r awn Tilt; -w (494) p« m clic) 7-* ' TTY cta * 14)(**c1V-I 1-Kii I ru-'1q,+let) 3c471/fifitff cl I. 31Plui MIT ra-404. a~lu ti 1I *tq *11-AR I (0) trftwfrsff A'tPARerr iwt \let) RI (7) 1-4-4k T1 641 fq-0-*itzr T4t * (-PM f4r-4ff E.= 0, Ey = 30 cos (2n x 108 t (1) 1tx), E z = 0 t *TT *1. E 3rft 441e.t t**-n MIT x 41ex 4 PHE-07 6 wkritszi, 4akui fell CST ~tid~ AtTitta. WAR I

7 2. iwt 31-Fr *PA : () ABCD t t 'WITH 0.02 m f43.11 A, B MIT C 1T sh&ri: 16 x 10-9 C, -16 x 10-9 C Wan 32 x 10-9 C altart we D tritztrat 14qii Auffta ttnr 1 10 (ii) 641 sl***4.1) 1T 1 31 aaf *tr- 4 smrct., 7T314 Piot ogctn *tr4r I NA 7' ITTIT >c 0*R : Priv, elc11 Tfr A1 41 r 3rd5PA 4I ITRT qtr atkf* areqt 1-44tzt 04* eiotcb "aj- rw AfA 't-efit nevi mu %Ili -tug TRT4-di WAT ai-dk Gicw I (a) (i) 5.0 mm fi'art arc; -A, A MU Wee' *I tett I M tm tit 1-42r4 Ts. tifkcnrod *ii* wr am * ifr tachi-zid =rnr,316 mit tatrzi Wr TR, WR tic14 IR dts4 ITTR atitit with t I 3+3 4fg sb s airfl 7W xi 4).- *trzr TR 0.40 mt t I 7fit linaehi reo tirt TATTfT4 0.4 A', *t-14 'SA cm %a A ( iiikchicia AP4R I 4 PHE-07 7 P.T.O.

8 4. itirt : *17 Ac trititrlim AY* I t TRP4 -{ fatg, TAT 1-4itt Taq Turri 3TReffa. t Izift f4s-4,-#q qtr, ct3fftgitr #q 4 *-4eff 2.2 cm \Telt al Iffrwrt trat 4 Tic,' t ITa T-471 W4T r ardcfm. *PAR zdt -NER*1TAT iiui 15 kvm 1 c TTtgilrzl. x 10-3 Tt I *MT R-4`4T WWI -gt 3kR1 (41ff) * ckido 3T-4-*-F Tq 4 foftir 311 *rr kv-ilcbtui trr ARI. 1: tift4fff ttr4r I 4+6 T fhfg. cfrfich : f9:,e1j-11-1 = 9.1 x kg = 1.7 x kg ra-4-0q T3Tf-4` x C 1 iinc o =9x109 Nm2 C = 4a x 10-7 NA x Fm 1 - PHE ,500

BACHELOR OF SCIENCE (B.Sc.) Term-End Examination December, 2016

No. of Printed Pages : 8 I PHE-13 I BACHELOR OF SCIENCE (B.Sc.) Term-End Examination December, 2016 01 165 PHYSICS PHE-13 : PHYSICS OF SOLIDS Time : 2 hours Maximum Marks : 50 Note : Attempt all questions.