Title 8.ELECTROMAGNETIC WAVES - Questions.pdf ✅

8.ELECTROMAGNETIC WAVES (1.)In an electromagnetic wave, the electric and magnetizing fields are 100 Vm−1 and 0.265 Am−1 . The maximum energy flow is (a.) 26.5 Wm−2 b) 36.5 Wm−2 c) 46.7 Wm−2 d) 765 Wm−2 (2.)An electromagnetic radiation has an energy of 13.2 keV. Then the radiation belongs to the region of (a.) Visible light b) Ultraviolet c) Infrared d) X-ray (3.)A cube of edge a has its edges parallel to x, y and z-axis of rectangular coordinate system. A uniform electric field E⃗ is parallel to y-axis and a uniform magnetic field is E⃗ parallel to x-axis. The rate at which flows through each face of the cube is (a.) a 2.EB 2μ0 parallel to x − y plane and zero in others b) a 2EB μ0 parallel to x − y plane and zero in others c) a 2EB 2μ0 from all faces d) a 2EB 2μ0 parallel; to y − z faces and zero in others (4.)The relation between electric field vector E, the displacement vector D and the polarization vector P for a dielectric placed in electric field E is given by (a.) P = ε0E + D b) P = D + E c) D = ε0E + Pd) E = D + P (5.)Maxwell in his famous equation of electromagnetism introduced the concept of (a.) AC current b) DC current c) Displacement current d) Impedance (6.)Which of the following is absorbed by the ozone layer? (a.) Only gamma rays b) Visible light c) Radio Waves d) Ultraviolet rays (7.)The frequency 1057 MHz of radiation arising from two close energy levels in hydrogen belongs to (a.) Radio waves b) Infrared waves c) Micro waves d) γ − rays (8.)A radiowave has a maximum magnetic field induction of 10−4 T on arrival at a receiving antenna. The maximum electric field intensity of such a wave is (a.) Zero b) 3 × 104 Vm−1 c) 5.8 × 10−4 T d) 3.0 × 10−5 T (9.)A lasser beam is sent to the moon and reflected back to earth by ay mirror placed on the moon by an astronaut. If the moon is 384000 km from earth, how long does it take the light to make the round trip? (a.) 5 min b) 2.5 min c) 2.5 s d) 500 s (10.)The magnetic field of an Electromagnetic Wave is given by BY = 3 × 10−7 sin (103x + 6.29 × 1012t). The wavelength of the Electromagnetic Wave is (a.) 6.28 cm b) 3.14 cm c) 0.63 cm d) 0.32 cm (11.)An earth orbiting satellite has solar energy collecting panel with total area 5 m2 . If solar radiations are perpendicular and completely absorbed, the average force associated with the radiation pressure is (Solar constant= 1.4 kWm−2 ) (a.) 2.33 × 10−3 N b) 2.33 × 10−4 N c) 2.33 × 10−5 N d) 2.33 × 10−6 N (12.)The waves which have revolutionized telecommunication in more recent time, are (a.) Micro wave b) Radio waves c) Light waves d) TV waves (13.)The electric field for a plane electromagnetic wave travelling in the positive z-direction is represented by which one of the following?
(a.) k̂ 1E0e i (kz − ωt + φ) b) î1E0e i (kx − ωt + φ) c) î1E0e i (kz + ωt + φ) d) k̂ 1E0e i (kz + ωt + φ) (14.)If the earth did not have atmosphere, its surface temperature on a day time would be (a.) Higher b) Lower c) Same as now d) Not sure (15.)The correct sequence of the increasing wavelength of the given radiation sources is (a.) Radioactive sources, X-ray tube, crystal oscillator, sodium vapour lamp b) Radioactive source, X-ray tube, sodium vapour lamp, crystal oscillator c) X-ray tube, radioactive source, crystal oscillator, sodium vapour lamp d) X-ray tube, crystal oscillator, radioactive source, sodium vapour lamp (16.)Which of the following electromagnetic waves have the longest wavelength? (a.) Heat waves b) Light waves c) Radio waves d) Ultraviolet waves (17.)Which of the following rays is emitted by a human body? (a.) X-rays b) UV rays c) Visible rays d) IR rays (18.)The unit of expression μ0ε0 are (a.) ms −1 b) m2 s −2 c) s 2m−2 d) sm−1 (19.)If c is the speed of Electromagnetic Waves in vacuum, its speed in a medium of dielectric constant K and relative permeability μ, is (a.) v = 1 √μr,K b) v = c√μrcK c) v = c √μr,K d) v = K √μr,c (20.)A charged particle with charge q enters a region of constant, uniform and mutually orthogonal fields E and B with a velocity v perpendicular to both E and B, and comes out without any change in magnitude or direction of v. Then (a.) v = E × B/B 2b) v = B × E/B 2 c) v = E × B/E 2d) v = B × E/E 2 (21.)The energy of X-ray photon is 2200 eV. Its frequency would be (a.) 5.3 × 1016 Hz b) 5.3 × 1017 Hz c) 5 × 1017 Hz d) 5 × 1016 Hz (22.)A charged particles oscillates about its mean equilibrium position with a frequency of 109 Hz. Frequency of the Electromagnetic Waves produced by the oscillator is (a.) 10 Hz b) 105 Hz c) 109 Hz d) 1010 Hz (23.)All components of the Electromagnetic Spectrum in vacuum have the same (a.) Energy b) Velocity c) Wavelength d) Frequency (24.)If a source is transmitting electromagnetic wave of frequency 8.2 × 106 Hz, then wavelength of the electromagnetic waves transmitted from the source will be (a.) 36.6 m b) 40.5 m c) 42.3 m d) 50.9 m (25.)Given the wavefunction (in SI units) for a wave to be ψ(x,t) = 103 sin π(3 × 106 x − 9 × 1014 t) The speed of the wave is (a.) 9 × 1014 ms −1 b) 3 × 108 ms −1 c) 3 × 106 ms −1 d) 3 × 107 ms −1 (26.)The electric field of plane electromagnetic wave in vacuum is represented by E⃗ x = 0; E⃗ y = 0.5 cos[2π × 108(t − x/c)]: E⃗ z = 0 What is the direction of propagation of electromagnetic waves? (a.) Along x − z direction b) Along y-direction c) Along x-direction d) A long y − z direction (27.)Which of the following has zero average value in a plane electromagnetic wave? (a.) Kinetic energy b) Magnetic field c) Electric field d) Both (b) and (c)
(28.)The charge of a parallel plate capacitor is varying as q = q0 sin 2πft. The plates are very large and close together (area= A, separation= d). Neglecting edge effects, the displacement current through the capacitor is (a.) d Aε0 b) d ε0 sin2πft c) 2πfq0 cos 2πft d) 2πfq0 ε0 cos 2π ft (29.)Radio wave diffract around building although light waves do not. The reason is that radio waves (a.) Travel with speed target than c b) Have much larger wavelength than light c) Carry news d) Are not electromagnetic waves (30.)If ε0 and μ0 represent the permittivity and permeability of vacuum and ε and μ represent the permittivity and permeability of medium, then refractive index of the medium is given by (a.) √ μ0ε0 με b) √ με μ0ε0 c) √ μ μ0ε0 d) √ μ0ε0 μ (31.)The magnetic field between the plate of a capacitor where r > R is given by (where r is the distance from the axis of plates and R is the radius of each plate of capacitor) (a.) μ0iDr 2πR2 b) μ0iD 2πR c) μ0iD 2πr d) Zero (32.)A TV tower has a height of 100 m. How much population is covered by the TV broadcast if the average population density around the tower is 100 km−2 (radius of the earth= 6.37 × 106 m) (a.) 4 lakh b) 4 billion c) 40,000 d) 40 lakh (33.)A radiation of energy E falls normally on a perfectly reflecting surface. The momentum transferred to the surface is (a.) E c b) 2E c c) Ec d) E c 2 (34.)A. The wavelength of microwaves is greater than that of UV-rays. B. The wavelength of IR rays is lesser than that of UV-rays. C. The wavelength of microwaves is lesser than that of IR-rays. D. Gamma rays have shortest wavelength in the Electromagnetic Spectrum. Of the above statements (a.) A and B are true b) B and C are true c) C and D are true d) A and D are true (35.)Molybdenum is used as a target element for the production of X-rays because it is (a.) Light and can easily defect electrons b) Light and can absorb electrons c) A heavy element with a high melting point d) An element having high thermal conductivity (36.)The ozone layer absorbs (a.) Infrared radiations b) Ultraviolet radiations c) X-rays d) γ-rays (37.)In a phase electromagnetic wave, the electric filed oscillates sinusoidally at a frequency of 2.0 × 1010 Hz and amplitude 48 Vm−1 . The wavelength of the wave is (a.) 24 × 10−10 m b) 1.5 × 10−2 m c) 4.16 × 108 m d) 3 × 108 m (38.)A point source of Electromagnetic radiation has an average power output of 1500 W. The maximum value of electric field at a distance of 3 m from this source in Vm-1- is (a.) 500 b) 100 c) 500 3 d) 250 3 (39.)The refractive index and the permeability of a medium are respectively 1.5 and 5 × 10−7Hm−1 . The relative permittivity of the medium is nearly (a.) 25 b) 15 c) 81 d) 6 (40.)The wavelength of X-rays lies between (a.) Maximum to finite limits b) Minimum to certain limits c) Minimum to infinite limits d) Infinite to finite limits (41.)For EM wave prorogating along x-axis, Emax = 30 Vm−1 . what is maximum value of magnetic field?
(a.) 10-7 T b) 10-8 T c) 10-9 T d) 10-6 T (42.)An electromagnetic wave, going through vacuum is described by E = E0 sin(kx − ωt) Which of the following is independent of wavelength? (a.) k b) ω c) k/ω d) kω (43.)A radio wave of frequency 90 MHz enters a ferrite rod. If εr = 103 and μr = 10, then the velocity and wavelength of the wave in ferrite are (a.) 3 × 108 ms −1 ; 3.33 × 10−2 m b) 3 × 106 ms −1 ; 3.33 × 10−2 m c) 3 × 108 ms −1 ; 3.33 × 10−1 m d) 3 × 107 ms −1 ; 3.33 × 10−3 m (44.)A plane Electromagnetic Wave of frequency 30 MHz travels in free space along the x-direction. The electric field component of the wave at a particular point of space and time E=6 Vm-1 along y-direction. Its magnetic field component B at this point would be (a.) 2 × 10−8 T along z-direction b) 6 × 10−8 T along x-direction c) 2 × 10−8 T along y-direction d) 6 × 10−8 T along z-direction (45.)The electric field (in NC −1 ) in an electromagnetic wave is given by E = 50 sin ω (t − x/c). The energy stored in a cylinder of cross-section 10 cm2 and length 100 cm, along the x-axis will be (a.) 5.5 × 60−12 J b) 1.1 × 10−11 J c) 2.2 × 10−11 J d) 1.65 × 10−11 J (46.)Height h of transmitter antenna when R is radius of earth to have range d is (a.) d 2 /2R b) √2dR c) 2d 2 /R d) 2R 2 /d (47.)In a plane electromagnetic wave propagating in space has an electric field of amplitude 9 × 103 Vm−1 , then the amplitude of the magnetic field is (a.) 2.7 × 1012 T b) 9.0 × 10−3 T c) 3.0 × 10−4 T d) 3.0 × 10−5 T (48.)The shortest wavelength of X-rays emitted from an X-rays tube depends upon (a.) Nature of the gas in the tube b) Voltage applied to tube c) Current in the tube d) Nature of target of the tube (49.)A large parallel plate capacitor, whose plates have an area of 1 m2 and are separated from each other by 1 mm, is being charged at a rate of 25 Vs −1 . If the dielectric between the plates has the dielectric constant 10, then the displacement current at this instant is (a.) 25 μA b) 11 μA c) 2.2 μA d) 1.1 μA (50.)The Maxwell’s four equations are written as (i)∮ E⃗ ∙ ds ⃗⃗⃗⃗ = q/ε0 (ii)∮ B⃗ ∙ ds ⃗⃗⃗⃗ = 0 (iii)∮ E ∙ dl ⃗⃗⃗ = − d dt ∮B⃗ ∙ ds ⃗⃗⃗⃗ s (iv)∮ B⃗ ∙ dl ⃗⃗⃗ = μ0I + μ0ε0 d dt ∮ E⃗ . ds ⃗⃗⃗⃗ s The equation which have sources of E⃗ and B⃗ are (a.) (i), (ii), (iii) b) (i), (ii) c) (i)and (iii) only d) (i)and (iv) only (51.)Which of the following shows green house effect? (a.) Ultraviolet rays b) Infrared rays c) X-rays d) None of these (52.)If a source is transmitting Electromagnetic Waves of frequency 8.196 × 106 Hz, then the wavelength of the Electromagnetic Waves transmitted from the source will be (a.) 5090 cm b) 4050 cm c) 4230 cm d) 3660 cm (53.)The electric field of an electromagnetic wave travelling through vacuum is given by the equationE = E0 sin(kx − ωt). The quantity that is independent of wavelength is (a.) k ω b) kω c) ω d) k (54.)If ε0 and μ0 are the electric permittivity and magnetic permeability of free space and ε and μ are the corresponding quantities in the medium, the index of refraction of the medium in terms of above parameter is (a.) εμ ε0μ0 b) ( εμ ε0μ0 ) 1/2