Class XII - Physics Electromagnetic Waves Chapter-wise Problems

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1 Class XII - Physis Eletromagneti Waves Chapter-wise Problems Multiple Choie Question :- 8 One requires ev of energy to dissoiate a arbon monoxide moleule into arbon and oxygen atoms The minimum frequeny of the appropriate eletromagneti radiation to ahieve the dissoiation lies in (a) visible region (b) infrared region () ultraviolet region (d) mirowave region 8 A linearly polarized eletromagneti wave given as E = Eoˆos i ( kz ωt) is inident normally on a perfetly refleting infinite wall at z = a Assuming that the material of the wall is optially inative, the refleted wave will be given as (a) E = E ˆi os ( kz ωt) r o (b) E = Eoˆos i ( kz + ωt) r Page of 7

2 84 The eletri field intensity produed by the radiations oming from W bulb at a 3 m distane is E The eletri field intensity produed by the radiations oming from 5 W bulb at the same distane is (a) E (b) E () E (d) E 85 If E and B represent eletri and magneti field vetors of the eletromagneti wave, the diretion of propagation of eletromagneti wave is along (a) E (b) B () B E (d) E B 86 The ratio of ontributions made by the eletri field and magneti field omponents to the intensity of an EM wave is (a) : (b) : () : (d) : 87 An EM wave radiates outwards from a dipole antenna, with E as the amplitude of its eletri field vetor The eletri field E whih Page of 7

3 88 An eletromogneti wave travels in vauum along z diretion: E = ( E ˆ ˆ) os ( ) i+ Ej kz ωt Choose the orret options from the following: (a) The assoiated magneti field is given as B = ( E ˆ ˆ i Ej) os (kz-ωt) (b) The assoiated magneti field is given as B = ( E ˆ E ˆ i j) os (kz-ωt) () The given eletromagneti field is irularly polarised (d) The given eletromagneti wave is plane polarised 89 An eletromagneti wave travelling along z-axis is given as: E= E os (kz - ωt) Choose the orret options from the following; (a) The assoiated magneti field is given as B = ˆ = ( ˆ ) k E ω k E (b) The eletromagneti field an be written in terms of the assoiated magneti field as E = ( B k ˆ ) () ke ˆ =, kˆ B= (d) kˆ E=, kˆ B = 8 A plane eletromagneti wave propagating along x diretion an have the following pairs of E and B (a) E x, B y (b) E y, B z () B x, E y (d) E z, B y Page 3 of 7

4 83 An EM wave of intensity I falls on a surfae kept in vauum and exerts radiation pressure p on it Whih of the following are true? (a) Radiation pressure is I/ if the wave is totally absorbed (b) Radiation pressure is I/ if the wave is totally refleted () Radiation pressure is I/ if the wave is totally refleted (b) Radiation pressure is in the range I/ < p < I/ for real surfaes VSA 84 Why is the orientation of the portable radio with respet to broadasting station important? 85 Why does mirowave oven heats up a food item ontaining water moleules most effiiently? 86 The harge on a parallel plate apaitor varies as q = q os πνt The plates are very large and lose together (area = A, separation = d) Negleting the edge effets, find the displaement urrent through the apaitor? 87 A variable frequeny a soure is onneted to a apaitor How will the displaement urrent hange with derease in frequeny? 88 The magneti field of a beam emerging from a filter faing a floodlight is given by B = 8 sin ( 7 z 36 5 t) T What is the average intensity of the beam? 89 Poynting vetors S is defined as a vetor whose magnitude is equal to the wave intensity and whose diretion is along the diretion of wave propogation Mathematially, it is given by S = E B μ Show the nature of S vs t graph Page 4 of 7

5 8 Eletromagneti waves with wavelength (i) λ is used in satellite ommuniation (ii) λ is used to kill germs in water purifies (iii) λ 3 is used to detet leakage of oil in underground pipelines (iv) λ 4 is used to improve visibility in runways during fog and mist onditions (a) Identify and name the part of eletromagneti spetrum to whih these radiations belong (b) Arrange these wavelengths in asending order of their magnitude () Write one more appliation of eah 83 Show that average value of radiant flux density S over a single period T is given by S = E μ 84 You are given a μf parallel plate apaitor How would you establish an instantaneous displaement urrent of ma in the spae between its plates? 85 Show that the radiation pressure exerted by an EM wave of intensity I on a surfae kept in vauum is I/ 86 What happens to the intensity of light from a bulb if the distane from the bulb is doubled? As a laser beam travels aross the length of a room, its intensity essentially remains onstant Page 5 of 7

6 LA 88 An infinitely long thin wire arrying a uniform linear stati harge density λ is plaed along the z-axis (Fig 8) The wire is set into motion along its length with a uniform veloity ˆ z v =v k Calulate the poynting vetor S = ( E B ) μ o Z a y x V 89 Sea water at frequeny ν = 4 8 Hz has permittivity ε 8 ε o, permeability μ μ o and resistivity ρ = 5 Ω m Imagine a parallel plate apaitor immersed in sea water and driven by an alternating voltage soure V(t) = V o sin (π νt) What fration of the ondution urrent density is the displaement urrent density? 83 A long straight able of length l is plaed symmetrially along z-axis and has radius a(<<l) The able onsists of a thin wire and a o-axial onduting tube An alternating urrent I(t) = I o sin (πνt) flows down the entral thin wire and returns along the o-axial onduting tube The indued eletri field at a distane s from s the wire inside the able is E( st, ) =μ ˆ oioνos( πνt) In k a (i) Calulate the displaement urrent density inside the able (ii) Integrate the displaement urrent density aross the rosssetion of the able to find the total displaement urrent I d (iii) Compare the ondution urrent I with the dispalement urrent I d o 83 A plane EM wave travelling in vauum along z diretion is given by E = E sin( kz ωt)ˆi and B = B sin( kz ωt) ˆj (i) Evaluate Edl over the retangular loop 34 shown in Fig 8 (ii) Evaluate Bds over the surfae bounded by loop 34 Fig 8 Page 6 of 7

7 d B (iii) Use equation Edl φ = to prove dt E B = (iv) By using similar proess and the equation dφ dt E Bdl = μi + ε, prove that = μ ε x h A plane EM wave travelling along z diretion is desribed by E = E sin( kz ω t)ˆi and B = B sin( kz ω t)ˆj Show that (i) The average energy density of the wave is given by y Fig 8 z (ii) u B μ av = εe The time averaged intensity of the wave is given by I = ε E av Page 7 of 7

not to be republished NCERT ELECTROMAGNETIC WAVES Chapter Eight MCQ I

not to be republished NCERT ELECTROMAGNETIC WAVES Chapter Eight MCQ I Chapte Eight ELECTROMAGNETIC WAVES MCQ I 8 One equies ev of enegy to dissoiate a abon monoxide moleule into abon and oxygen atoms The minimum fequeny of the appopiate eletomagneti adiation to ahieve the