Tiêu đề 35. Electromagnetic waves Med.pdf ✅

1. The displacement current was first postulated by (a) Ampere (b) Maxwell (c) Hertz (d) Marconi 2. The fundamental source of e. m. waves (a) is varying magnetic field (b) constant magnetic and electric fields (c) oscillations of electric charge (d) is planets 3. An accelerated electric charge emits (a)  – rays (b)  – rays (c) e.m. waves (d) none of the above 4. Electromagnetic waves in nature are (a) longitudinal (b) longitudinal stationary (c) transverse (d) transverse – stationary 5. The speed of e. m. waves is given by the relation (a)   (b)  0 0 (c) 1/  (d) 1/ ( )  0 0 6. Choose the only wrong statement from the following about electromagnetic waves (a) are transverse (b) travels free space at the speed of light (c) are produced by accelerating charges (d) travel with the same speed in all media 7. Electromagnetic waves (a) are longitudinal waves (b) travel in free space at the speed of light (c) are produced by charges moving with uniform velocity (d) travel with the same speed in all media 8. An accelerated charge (a) emits an electromagnetic wave (b) produces stationary electric and magnetic fields (c) produces a gravitational field (d) none of the above 9. n an electromagnetic wave, electric field E and magnetic field B are (a) mutually perpendicular to each other (b) all parallel (c) at 300 to each other (d) depends upon polarization 10. If E and B be the electric and magnetic fields of electromagnetic waves, then the direction of propagation of e. m. wave is along the direction of (a) E (b) B (c) E   (d) None of the above 11. Which of the following pairs of space and time varying E and B fields would generate a plane electromagnetic wave travelling in the Z– direction (a) Ex , By (b) Ey , Bx (c) Ex , Bz (d) Ez , Bx 12. Electromagnetic wave obey the principle of (a) superposition (b) interference (c) 1 and 2 both (d) none of the above 13. Hertz produced electromagnetic wave by using (a) L C R circuit (b) C R circuit (c) L C circuit (d) None of the above 14. Choose the correct statement about electromagnetic waves (a) they are supersonic waves (b) they are the electrically charged particles (c) they travel with the speed of light (d) they can only be produced in laboratory. 15. Visible range of light has wavelength in cm is (a) 3 x 10–6 to 10–10 (b) 7 x 10–5 to 4 x 10–5 (c) 4 x 10–5 to 3 x 10–6 (d) 6 x 104 to 1.5 x 103
16. The following electromagnetic waves has the shortest wavelength (a)  – rays (b) x – rays (c) ultraviolet rays (d) microwaves 17. Which of the following has the longest wavelength ` (a) infrared light (b) ultraviolet light (c) microwaves (d) X–rays 18. Only microwaves are used for (a) television (b) radio transmission (c) radar system (d) all the above 19. The earth’s atmosphere is richer in (a) infrared radiation (b) ultraviolet radiations (c) visible radiations (d) blue colour radiations 20. Greenhouse effect is due to (a) visible radiations (b) red colour radiation (c) Green colour radiation (d) infra - red radiation 21. Greenhouse effect keeps the earth surface (a) cold in night (b) dusty and cold (c) warm in night (d) moist in night 22. Ozone layer protectes the living organism from (a) ultraviolet radiations (b) unfra –red radiations (c) X–rays (d) all the radiations 23. Practically ozone layer absorbs the radiation of wavelength (a) less than 3 x 10–7 m (b) greater than 3 x 10–7 m (c) equal to 3 x 10–7 m (d) all the above 24. Frequency of a wave is 6 × 1015 Hz. The wave is (a) radioactive (b) microwave (c) X-rays (d) ultraviolet 25. If the wavelength of light is 4000 Å, then the number of waves in 1 mm length will be (a) 25 (b) 0.25 (c) 0. 25 × 104 (d) 25 × 104 26. What is the range of frequency for ultrasonic wave ? (a) 1kHz (b) 5kHz (c) 50 kHz (d) 10 kHz 27. If c is the speed of electromagnetic waves in vacuum, its speed v in a medium of dielectric constant k and relative permeability r , is (a) r 1 v k =  (b) r v c k =  (c) r c v k =  (d) r k v c =  28. Which one of the following is not an electromagnetic waves ? (a) X-rays (b) gamma rays (c) cathode rays (d) infrared rays 29. The dimensions of 1 2 0 E 2 (0 : permittivity of free space; E : electric field) is (a) M L T–1 (b) M L2 T –2 (c) M L–1 T –2 (d) M L2 T –1 30. The speed of electromagnetic waves in vacuum (a) depends upon the source of radiation (b) increases as we move from -rays to radiowves (c) decreases as we move from -rays to radiowaves (d) is same for all of them 31. If   x , and m represent the wavelengths of visible light, x- rays and microwave respectively then
(a) m > x >  (b)  > m > x (c)  > x > m (d) m >  > x 32. The frequency of light wave in a material is 2 × 1014 Hz and wavelength is 5000 Å. The refractive index of material will be : (a) 1.40 (b) 1.50 (c) 3.00 (d) 1.33 33. The electric and magnetic fields of an electromagnetic wave are : (a) in phase and parallel to each other (b) in opposite phase and perpendicular to each other (c) in opposite phase and parallel to each other (d) in phase and perpendicular to each other. 34. The velocity of electromagnetic radiation in a medium of permittivity 0 and permeability 0 is given by : (a) 0 0   (b)   0 0 (c) 0 0 1   (d) 0 0   35. Which of the following is the infra-red wavelength ? (a) 10–4 cm (b) 10–5 cm (c) 10–6 cm (d) 10–7 cm 36. According to maxwell's hypothesis, a changing electric field gives rise to (a) an e.m.f (b) electric current (c) magnetic field(d) pressure gradiant 37. Maxwell in his famous equation of electromagnetism introduced the concept of (a) a.c. current (b) d.c. current (c) displacement current (d) impedance 38. Sodium lamps are used in foggy conditions because (a) yellow light is scattered less by the fog particles (b) yellow light is scattered more by the fog particles (c) yellow light is unaffected during its passage throught the fog (d) wavelength of yellow light is the mean of the visible part of the spectrum. 39. The pressure exerted by an electromagnetic wave of intensity I (watt / m2 ) on a non-reflecting surface is [c is the velocity of light] (a) I c (b) I c 2 (c) I / c (d) I / c2 40. An electromagnetic wave of frequency v = 3.0 MHz passes vacuum into a dielectric medium with permittivity  = 4.0, then (a) wavelength is doubled and the frequency remains unchanged (b) wavelength is doubled and frequency becomes half (c) wavelength is halved and frequency remains unchanged (d) wavelength and frequency both remain unchanged 41. The S.I unit of displacement current is (a) H (b) A (c) Fm–1 (d) C 42. The speed of electromagnetic waves is independent of (a) wavelength (b) frequency (c) intensity (d) medium, in which it travels  Dimension of 0 0 is : (a) LT–1 (b) L –1 T (c) L 2 T –2 (d) L –2 T 2 44. If 0 and 0 are the electric permittivity and magnetic permeability in free space,  and  are the corresponding quantities in a medium, then index of refraction of the medium is (a) 0 0    (b) 0   (c) 0 0    (d) 0 0    45. Red light differs from blue light while traveling in vacuum is
(a) speed. (b) frequency (c) intensity (d) amplitude 46. If an electromagnetic wave propagating through vacuum is described by following then E = E0 sin (kx – t) ; B = B0 sin (kx – t) (a) E0 k = B0  (b) E0B0 =  k (c) E0 =B0 k (d) E0 B0 =  / k 47. Which of the following is independent of wavelength ? (k = propagation constant,  = angular frequency) (a) k (b)  (c) k (d) k /  48. A magnetic field can be produced by (a) A charge at rest only (b) A moving charge only (b) Time varying electric field (d) both by (b) and (c) 49. An electric charge in uniform motion produces (a) an electric field only (b) a magnetic field only. (c) both electric and magnetic field (d) no such field at all. 50. Which of the following radiation form the part of electromagnetic spectrum (a) alpha rays (b) beta rays (c) cathode rays (d) gamma rays 51. The oscillating electric and magnetic field vectors of electromagnetic wave are oriented along (a) The same direction and in phase (b) The same direction but have a phase difference of 90o (c) mutually perpendicular direction and are in phase (d) mutually perpendicular directions but has a phase difference of 90o 52. Which one of the following electromagnetic radiations have the smallest wavelength ? (a) ultraviolet waves (b) X-rays (c) -rays (d) microwaves 53. Which of the following rays has minimum frequency ? (a) U.V-rays (b) X-rays (c) micorwaves (d) infra-red-rays 54. An accelerated electron would produce (a) -rays (b) -rays (c) -rays (d) e.m. rays 55. The frequencies of X-rays, -rays and ultraviolt rays are respectively a, b and c. Then (a) a < b, b > c (b) a > b, b > c (c) a > b, b < c (d) a < b, b < c. 56. When light travels from air to water, which parameter does not change ? (a) wavelength (b) frequency (c) velocity (d) all of these 57. The velocity of light in vacuum can be changed by changing (a) frequency (b) amplitude (c) wavelength (d) none of these. 58. Which of the following statement is wrong (a) Ultra-violet rays have a wavelength longer than infra-red rays. (b) Infra-red rays travel with the same velocity as visible light. (c) Infra-red can be focussed by a lens and can be reflected by a mirror just as visible light (d) Infra-red rays have more heating power than visible light rays 59. In an electromagnetic wave, the electric and magnetic fields are 100 Vm–1 and 0.265 Am–1 . The maximum energy flow is (a) 26.5W/m2 (b) 36.5W/m2 (c) 46.7 Wm2 (d) 765 W/m2