-rays,infrared rays, microwaves, yellow light, radio waves.

Transcription

1 BHUJ-JAMNAGAR CLUSTER LEVEL PHYSICS WORKSHOP CLASS-XII ELECTROMAGNETIC WAVES One maks questions Q.1 The chaging cuent fo a capacito is.5 A. what is the isplacement cuent acoss its plates? Displacement cuent =chaging cuent =.5 A. Q. A vaiable fequency a.c. souce is connecte to a capacito. Will the isplacement cuent incease o ecease with incease in fequency? Incease in fequency causes ecease in impeance of the capacito an consequent incease in the cuent. Hence isplacement cuent which equals conuction cuent inceases with incease in fequency of a.c. Q. What is the atio of velocities of light ays of wavelengths 4 Å an 8 Å in vacuum? Ratio=1, because light ays of both wavelengths tavel with the same velocity of x1 8 ms -1 in vacuum. Q.4 Name the electomagnetic aiation to which the following wavelengths belong: (a) 1 - m (b) 1 Å (a) Micowaves (b)x-ays. Q.5 Aange the following in the escening oe of wavelengths: -ays,infae ays, micowaves, yellow light, aio waves. Raio waves infae ays e light yellow light -ays. Q.6 If the wavelength of an electomagnetic aiation is ouble, what will happen to the enegy of photons? Enegy of a photon, E hv hc When the wavelength of an electomagnetic aiation is ouble, the enegy of the photons is halve. Q.7 How oes a chage q oscillating at cetain fequency pouce electomagnetic waves? Oscillating chage pouces sinusoial vaiation of electic an magnetic fiel, which in tun pouces electomagnetic wave. Q.8 Ientify the following electomagnetic aiation as pe the wavelength given below. (i) 1-1 m (ii)1-4 m (iii)1 6 m (i) Gamma ays, (ii)infae ays, (iii)raio wave. Q.9 Expess velocity of popagation of e.m. waves in tems of the peak value of electic & magnetic fiels. o Q.1 What is the elation between conuction cuent an isplacement cuent. I C = I D Two maks questions Q.1 What is isplacement cuent? Why was this concept intouce? Displacement cuent - It is that cuent which comes into existence, wheneve the electic fiel an hence the electic flux changes with time. It is equal to times the ate of change of electic flux though a given suface E E I A t t

2 Maxwell intouce the concept of isplacement cuent fo the following easons: (i) To make the Ampee's cicuital law logically consistent. (ii) To satisfy the popety of continuity of electic cuent along any close path. Q. A paallel plate capacito is being chage. Show that the isplacement cuent acoss an aea in the egion between the plates an paallel to it is equal to the conuction cuent in the connecting wies. q The conuction cuent I c is not continuous acoss the capacito gap as no chage t is tanspote acoss this gap. The isplacement cuent I is zeo outsie the capacito plates an in the gap, it has the value q E q I EA t t t t It is exactly the value of the conuction cuent in the lea wies. Thus the isplacement cuent satisfies the basic conition that the cuent is continuous. The sum I c I has the same value along the entie path (both insie an outsie the capacito plates), although iniviually the two cuents ae iscontinuous. Q. What is an electomagnetic wave? Expess it gaphically It is the wave aiate by an acceleate chage an which popagates though space as couple electic an magnetic fiels, oscillating pepenicula to each othe an to the iection of popagation of wave. The gaph showing e m wave is awn below Q.4 A plane electomagnetic wave tavels, in vacuum, along the y-iection. Wite (i) the atio of the magnitues, an (ii) the iections of its electic an magnetic fiel vectos. E (i) c, spee of light. B (ii) Fo an electomagnetic wave tavelling along y-iection, its electic an magnetic fiel vectos ae along z-axis an x-axis espectively. The iection of E B is same as that of iection of wave popagation an kˆ iˆ ˆj. Q.5 Name the following constituent aiations of electomagnetic spectum which : (i) Pouce intense heating effect. (ii) Is absobe by the ozone laye in the atmosphee. (iii) Is use fo stuying cystal stuctue. (iv) Pouce uing nuclea eactions (i) Infae waves.

3 (ii) Ultaviolet aiations. (iii) X-ays. (iv) Gamma ays Q.6 A paallel plate capacito has cicula plates, each of aius 5. cm. It is being chage so that electic fiel in the gap between its plates ises steaily at the ate of Vm s. What is the isplacement cuent? Displacement cuent, I E A t E t. E t A Q Electomagnetic waves tavel in a meium at a spee of.1 ms. The elative pemeability of the meium is 1.. Fin the elative pemittivity. Spee of an e. m.wave in a meium is given by 1 1 v 1 1 c c hence elative pemittivity, 8 c (1 ) 8 1. (1 ).5 Q.8 To which egions of the electomagnetic spectum the following wavelengths belong? Ǻ,5 Ǻ 1 Ǻ an 1.Ǻ Ǻ - ultaviolet ays 5 Ǻ - visible light 1 Ǻ - infae ays an 1.Ǻ - X ays Q.9 Which constituent aiations of electomagnetic spectum is use (i) In aa, (ii) To photogaph intenal pats of a human boy (iii)fo taking photogaphs uing nights an foggy conitions (iv) In wate puification (i) Micowaves, (ii) X ays, (iii)infae ays an (iv)uv ays Q.1 Fin the wavelength of electomagnetic wave of fequency 4X1 9 Hz in fee space. Give its two applications. =X1 8 / 4X1 9 = =.75m This wavelength coespons to micowaves an is use (i) micowave oven an(ii) aa Thee maks questions Q.1 Mention the vaious popeties of electomagnetic waves. These ae as follows: 1. The electomagnetic waves ae pouce by acceleate chages an o not equie any mateial meium fo thei popagation.

4 . The iections of oscillations of E an B fiels ae pepenicula to each othe as well as pepenicula to the iection of popagation of the wave. So the electomagnetic waves ae tansvese in natue.. The oscillations of E an B fiels ae in same phase. 4. All electomagnetic waves tavel in fee space with the same spee, c ms In a mateial meium, the electomagnetic waves tavel with the spee, 1 c c v, whee n is the efactive inex of the meium. n E 5. The amplitue atio of the electic an magnetic fiels is c B 6. The electomagnetic waves cay enegy as they tavel though space an this enegy is shae equally by the electic an magnetic fiels. The aveage enegy ensity of an e.m. wave is 1 B u ue ub E 7. Electomagnetic waves ae not eflecte by electic an magnetic fiels. 8. Electomagnetic waves show the popeties of eflection, efaction, intefeence, iffaction an polaization. Q. Mention the wavelength ange, fequency ange an souce of pouction of Raio Wave, Micowave, Infae Rays an Visible light, give the impotant popeties an uses of each pat. Raio waves These ae the e. m. waves of longest wavelength an minimum fequency. Wavelength ange - 6m to.1 m Fequency ange - Souce - 5 KHz to 1 MHz. Acceleate motion of chages in conucting wies o oscillating cicuits. Uses: (i) In aio an television communication systems. (ii) In aioastonomy. Micowaves - They ae the e. m. waves having wavelength next smalle to aiowaves. Due to thei shote wavelength, they can tavel as a beam. Wavelength ange -. m to 1 m Fequency ange - Souce Hz to1 Hz Oscillating cuents in special vacuum tubes like Klystonsan Magnetons. Uses: (i) In aa systems fo aicaft navigation. (ii)in long-istance communication systems via geostationay satellites. (iii) In micowave ovens. Infae ays These ays pouce heating effect, so they ae also known as heat waves o themal aiation. 6 Wavelength ange m to 1 m Fequency ange - 1 Hz to Hz

5 Souce - Hot boies an molecules. Uses: (i) In the emote contol of a TV o VCR. (ii) In geen houses to keep the plants wam. (iii) In haze photogaphy because infae waves ae less scattee than visible light by atmospheic paticles. (iv) Infae lamps in the teatment of muscula complaints. (v) In eaing the secet witings on the ancient walls (vi) In knowing the molecula stuctue. Visible light - It is vey small pat of the e.m. spectum towas which the human etina is sensitive. 7 7 Wavelength ange m to 41 m Fequency ange Hz to 71 Hz Souce - Raiate by excite atoms in ionize gas an incanescent boies. Uses: (i) It povies us the sensation of vision. (ii) It can cause photo-chemical eactions. Q. Giving the wavelength ange, fequency ange an souce of pouction of Ulta violet Rays, X-Rays an Gamma Rays, give the impotant popeties an uses of each pat. Ultaviolet ays - This egion of the e.m. spectum has wavelengths just shote than visible light. 7 7 Wavelength ange m to 1.51 m Fequency ange - 1 Hz to 1 Hz Souce - High voltage gas ischage tubes Uses: (i) In foo pesevation. (ii) In the stuy of invisible witings, foge ocuments an finge pints. (iii) In the stuy of molecula stuctue. X-ays - These e.m. waves have wavelengths just shote than ultaviolet light. As X-ays can pass though many foms of matte, so they have many useful meical an inustial applications. Wavelength ange m to 1 - m 18 Fequency ange - 1 Hz to 1 Hz Souce - Suen eceleation of fast moving electons by ametal taget. Uses: (i) In meical iagnosis because X-ays can pass though flesh but not though bones. (ii)in the stuy of cystals stuctue. (iii) In engineeing fo etecting faults, cacks, flaws an holes in the finishe metal poucts. (iv) In etective epatments to etect explosives, iamon, goletc. (v) In aiotheapy to cue untaceable skin iseases an malignant gowths. Gamma ays - These ae e.m. aiations of highest fequency ange an lowest wavelength ange. These ae most penetating e.m. waves.

6 14 1 Wavelength ange - 1 m to 1 m Fequency ange Hz to 1 Hz Souce - Raioactive nuclei an nuclea eactions. Uses: (i) In aiotheapy fo the teatment of malignant tumous. (ii) In the manufactue of polyethylene fom ethylene. (iii) To peseve foo stuffs fo a long time. (iv) To stuy the stuctue of atomic nuclei. Q.4 Electomagnetic waves with wavelength (i) 1 ae use to teat muscula stain. (ii) ae use by a FM aio station fo boacasting. (iii) ae use to etect factue in bones. (iv) 4 aeabsobe by the ozone laye of the atmosphee. Ientify an name the pat of electomagnetic spectum to which these aiations belong. Aange these wavelengths in eceasing oe of magnitue. ( i) 1 Infae aiations ii aiwaves iii iv X ays Ultaviolet ays 4 The wavelengths in eceasing oe of magnitue ae:. 1 4 Q.5 When can a chage act as a souce of electomagnetic waves? How ae the iections, of the electic an magnetic fiel vectos, in an electomagnetic wave, elate to each othe an to the iection of popagation of the wave? Which physical quantity, if any, has the same value fo waves belonging to the iffeent pats of the electomagnetic spectum? Only an acceleate chage can act as a souce of electomagnetic waves. The iections of electic an magnetic fiel vectos ae pepenicula to each othe as well as to iection of popagation of the wave. The wave spee in vacuum has the same value fo all the waves. Q.6 The magnetic fiel in a plane electomagnetic wave is given by 7 B y 1 sin.51 x 1.51 t tesla. (a) What is the wavelength an fequency of the wave? (b) Wite an expession fo the electic fiel. Given 7 B y 1 sin.51 x 1.51 t tesla On compaing with the stana equation, B Y B x sin vt

7 We get, Also, v v.9 1 Hz.9GHz (b) E cb Vm. The electic fiel is pepenicula to the iection of popagation (x-axis) an the iection of magnetic fiel (y-axis). So the expession fo electic fiel is 1 E z E sin.5 1 x 1.51 tvm m