Tiêu đề 23. Electromagnetic Waves.pdf ✅

1. Amplitude of electric field in EM wave is give as E0 = 300 V/m. Amplitude of magnetic field will be :- (1) 10–8 T (2) 10–6 T (3) 10–10 T (4) 10–7 T 2. Which of the following electromagnetic waves are used in telecommunication ? (1) X - rays (2) Infra red (3) Micro waves (4) Ultra violet 3 . Energy density of an EM wave having electric field E = E0 sin(  t – kx) is given by :- 4. The electric and the magnetic field, associated with an e.m. wave, propagating along the +z - axis, can be represented by :- 5. The electric field associated with an e.m. wave in vacuum is given by E i = ˆ 40 cos (kz–6× 108 t), where E, z and t are in volt/m, meter and seconds respectively. The value of wave factor k is : (1) 6m–1 (2) 3m–1 (3) 2m–1 (4) 0.5m–1 6. An EM wave of intensity I falls on a surface and completely absorbed. Pressure on the surface will be:- (1)I/C (2)I/2C (3)2I/C (4)I/3C 7. In an E.M. wave the average energy density is associated with :- (1) electric field only (2) magnetic field only (3) electric & magnetic fields equally (4) average energy density is zero 8. The nature of electromagnetic wave is :- (1) longitudinal (2) longitudinal stationary (3) transverse (4) transverse stationary 9. If vectors A t i t j = + cos sin   ˆ ˆ and cos sin ˆ ˆ 2 2 t t B i j   = + are functions of time, then the value of t at which they are orthogonal to each other is : (1) t = 0 (2) 4 t   = (3) 2 t   = (4) t   = 10. In an EM wave propagating along X- direction magnetic field oscillates at a frequency of 3×1010 Hz along Y-direction and has an amplitude of 10–7T.The expression for electric field will be :- (1) Ez = 30 sin 2  (100x – 3×1010 t) V/m (2) Ez = 300 sin 2  100x – 3×1010 t) V/m (3) Ey = 30 sin 2  (100x – 3×1010 t) V/m (4) Ez = 300 sin 2  (100x – 3×1010 t) V/m 11. The electric field strength in EM wave is104V/m. The magnitude of magnetic field strength(in tesla) will be :- (1) 104 (2) 3 × 1012 (3) 3.3 × 10–4 (4) 3.3 × 10–5 12. It is found that all electromagnetic signals sent from A towards B reach point C. The speed of electromagnetic signals in glass cannot be :- Electromagnetic Waves
(1) 1.0 × 108 m/s (2) 2.4 × 108 m/s (3) 2 × 107 m/s (4) 4 × 107 m/s 13. The rms value of the electric field of light coming from the Sun is 720 N/C. The average total energy density of the electromagnetic wave is (1) 4.58 × 10–6 J/m3 (2) 6.37 × 10–9 J/m3 (3) 81.35 × 10–12 J/m3 (4) 3.3 × 10–3 J/m3 14. The ratio of amplitude of magnetic field to the amplitude of electric field for an electromagnetic wave propagating in vacuum is equal to: (1) The ratio of magnetic permeability to the electric susceptibility of vacuum (2) Unity (3) The speed of light in vacuum (4) Reciprocal of speed of light in vacuum 15. Which of the following statement is true for displacement current :- (1) It is due to drift of electrons in a conductor (2) It is due to diffusion of electrons in a semi-conductor (3) It is due to change in electric flux with time (4) It is due to change in magnetic flux with time 16. When EM wave propagates through vacuum then (1) E-field leads B-field (2) E-field lags B-field (3) E-field and B-field are in the same phase (4) Energy is stored only in E-field 17. The velocity of electromagnetic wave is parallel to (1) B E (2) E B (3) E (4) B 18. The magnetic field in a plane electro magnetic wave is By = 1 × 10–7 sin(103 x– kt) tesla. If the expression for electric field is Ea = b sin(ex–dt) V/m, then the values of a, b,e and d are respectively :- (1) z, 60, 1 × 103 , 6 × 1011 (2) x, 30, 1 × 103 , 3 × 1011 (3) z, 30, 1 × 103 , 3 × 1011 (4) z, 30, 1 × 103 , 6 × 1011 19. Assertion :- The basic difference between different electromagnetic waves lies in their speeds in vacuum. Reason :- All electromagnetic waves travel with same wavelengths but different frequencies in vacuum. (1) A (2) B (3) C (4) D 20. The displacement current flows in the dielectric of a capacitor when the potential difference between its plates:- (1) is changing with time (2) is changing with distance (3) becomes zero (4) has assumed a constant value
KEY 1 – 10 2 3 2 1 3 3 3 3 4 1 11 – 20 4 2 1 4 3 1 2 3 4 1 Hints & Solutions: 1. E CB 0 0 = 2. Conceptual 3. Conceptual 4. Conceptual 5. W K C = 8 W = 6 108 C = 3 10 6. r F P A = 1 r dv P AC dt = 7. Conceptual 8. Conceptual 9. Conceptual 10. Conceptual 11. E CB 0 0 = 12. C V  = 8 C m s = 3 10 /  =1.5 13. 2 0 1 2 U E avg =  14. Conceptual 15. Conceptual 16. Conceptual 17. Conceptual 18. Conceptual 19. Conceptual 20. Conceptual
PREVIOUS YEAR QUESTIONS 1. Which of the following is positively charged? [2001] 2. Which of the following shows greenhouse effect? [2002] (a) Ultraviolet rays (b) Infrared rays (c) X-rays (d) None of these 3. Which of the following are not electromagnetic waves? [2003] (a) Cosmic rays (b) Gamma rays (c)  -rays (d) X-rays 4. If represent the wavelengths of visible light, .X-rays and microwaves respectively, then [2005] 5. The electric and magnetic field of an electromagnetic wave is |2007| (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 6. The velocity of electromagnetic radiation in a medium of permittivity and permeability , is given by [2008] 7. The electric field part of an electromagnetic wave in a medium is represented by |2009| wave is (a) moving alongy-direction with frequency Hz and wavelength 200 m. (b) moving along x-direction with frequency 106 Hz and wavelength 100 m (c) moving along x-direction with frequency 106 Hz and wavelength 200 m (d) moving along x-direction with frequency 106 Hz and wavelength 200 m 8. Which of the following statement is false for the properties of electromagnetic waves? [2010] (a) Both electric and magnetic field vectors attain the maxima and minima at the same place and the same time (b) The energy in electromagnetic wave is divided equally between electric and magnetic vectors (c) Both electric and magnetic field vectors are parallel to each other and perpendicular to the direction of propagation of wave (d) These waves do not require any material medium for propagation 9. The electric and the magnetic field, associated with an electromagnetic wave, propagating along the +z-axis, can be represented by [2011] 10. The decreasing order of wavelength of infrared, microwave, ultraviolet and gamma rays is [2011]