Title 10--electromagnetic-waves-.pdf ✅

Electromagnetic Waves 1. The energy of the em waves if of the order of 15keV. To which part of the spectrum does it belong ? (A) Ultraviolet (B) γ - rays (C) X-rays (D) Infra-red rays 2. A radiation of energy ' E ', falls normally on a perfectly reflecting surface. The momentum transferred to the surface is ( C = velocity of light ). (A) 2E C2 (B) E C2 (C) E C (D) 2E C 3. Light with an energy flux of 25 × 104Wm−2 falls on a perfectly reflecting surface at normal incidence. It the surface area is 15 cm2 , the average force exerted on the surface is : (A) 1.25 × 10−6N (B) 2.50 × 10−6N (C) 1.20 × 10−6N (D) 3.0 × 10−6N 4. The condition under which a microwave oven heats up a food item containing water molecules most efficiently is : (A) Microwaves are heat waves, so always produce heating. (B) Infra-red waves produce heating in a microwave oven. (C) The frequency of the microwaves must match the resonant frequency of the water molecules. (D) The frequency of the microwaves has no relation with natural frequency of water molecules. 5. An electromagnetic wave of frequency v = 3.0MHz passes from vacuum into a dielectric medium with relative permittivity ε = 4.0 then : (A) Wavelength is doubled and frequency becomes half (B) Wavelength is halved and frequency remains unchanged (C) Wavelength and frequency both remain unchanged (D) Wavelength is doubled and frequency unchanged 6. The electric field associated with an em wave in vacuum is given by E = iˆ40cos (kz − 6 × 108 t) where E, z and t are in volt/m, meter and seconds respectively. The value of wave vector k is : (A) 2m−1 (B) 0.5m−1 (C) 6m−1 (D) 3m−1 7. The ratio of amplitude of magnetic field to the amplitude of electric field for an electromagnetic wave propagating in vacuum is equal to : (A) The speed of light in vacuum (B) Reciprocal of speed of light in vacuum (C) The ratio of magnetic permeability to the electric susceptibility of vacuum (D) Unity 8. The electric and the magnetic field, associated with an em. wave, propagating along the +z-axis, can be represented by : (A) [E⃗ = E0i , B⃗ = B0j ] (B) [E⃗ = E0kˆ ,B⃗ = B0i ] (C) [E⃗ = E0jˆ,B⃗ = B0iˆ] (D) [E⃗ = E0jˆ,B⃗ = B0kˆ] 9. The decreasing order of wavelength of infrared microwave, ultraviolet and gamma rays is : (A) Microwave, infrared, ultraviolet, gamma rays (B) Gamma rays, ultraviolet, infrared microwaves (C) Microwaves, gamma rays, infrared, ultraviolet (D) infrared, microwave, ultraviolet, gamma rays 10. Which of the following statement is false for the properties of electromagnetic waves ? (A) Both electric and magnetic field vectors exist at 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 propagation of wave. (D) These waves do not require any material medium for propagation. 11. The electric field of an electromagnetic wave in free space is given by: E⃗ = 10cos (107 t + kx)jˆV/m, where t and x are in seconds and meters respectively. It can be inferred that (1) The wavelength λ is 188.4 m.
The wave number k is 0.33rad/m. (3) The wave amplitude is 10 V/m (4) The wave is propagating along +x direction. Which one of the following pairs of statements is correct? (A) (3) and (4) (B) (1) and (2) (C) (2) and (3) (D) (1) and (3) 12. The electric field part of an electromagnetic wave in a medium is represented by Ex = 0; Ey = 2.5 N C cos [(2π × 106 rad m ) t − (π × 10−2 rad s ) x] Ez = 0. The wave is : (A) Moving along x direction with frequency 106 Hz and wavelength 100 m (B) Moving along x direction with frequency 106 Hz and wavelength 200 m (C) Moving along −x direction with frequency 106 Hz and wavelength 200 m (D) Moving along y direction with frequency 2π × 106 Hz and wavelength 200 m 13. The velocity of electromagnetic radiation in a medium of permittivity ε0 and permeability μ0 is given by : (A) 1 √μ0ε0 (B) √ μ0 ε0 (C) √ ε0 μ0 (D) √μ0ε0 14. The electric and magnetic field of an electromagnetic wave are : (A) In opposite phase and perpendicular to each other (B) In opposite phase and parallel to each other (C) In phase and perpendicular to each other (D) In phase and parallel to each other 15. If λy, λx, and λm represent the wavelengths of visible light, X-rays and microwaves respectively, then : (A) λm > λx > λv (B) λm > λv > λx (C) λv > λx > λm (D) λv > λm > λx. 16. We consider the radiation emitted by the human body. Which one of the following statements is true ? (A) The radiation emitted is in the infra-red region (B) The radiation is emitted only during the day (C) The radiation is emitted during the summers and absorbed during the winters (D) The radiation emitted les in the ultraviolet region and hence is not visible 17. Which of the following rays are not electromagnetic waves ? (A) X-rays (B) γ-rays (C) β-rays (D) heat rays 18. The velocity of electromagnetic wave is parallel to : (A) B⃗ × E⃗ (B) E⃗ × B⃗ (C) E⃗ (D) B⃗ 19. What is the cause of green house effect? (A) infra-red rays (B) ultra violet rays (C) X-rays (D) radio waves. 20. Biological importance of ozone layer is : (A) It stops ultraviolet rays (B) Ozone layer reduces green house effect (C) Ozone layer reflects radio waves (D) Ozone layer controls O2/H2 ratio in atmosphere. 21. The frequency order for γ - rays (B), X-rays (A), UV rays (C) is : (A) B > A > C (B) A > B > C (C) C > B > A (D) A > C > B 22. Ozone layer blocks the radiations of wavelength (A) More than 3 × 10−7 m (B) equal to 3 × 10−7 m (C) less than 3 × 10−7 m (D) all of these 23. Wavelength of light of frequency 100 Hz (A) 4 × 106 m (B) 3 × 106 m (C) 2 × 106 m (D) 5 × 10−5 m 24. If ε0 and μ0 are the electric permittivity and magnetic permeability in a free space, ε and μ are the corresponding quantities in medium, the index and refraction of the medium is :
(A) √ ε0μ0 εμ (B) √ εμ ε0μ0 (C) √ ε0μ εμ0 (D) √ ε ε0 25. Which of the following electromagnetic radiations have the smaller wavelength? (A) X-rays (B) γ - rays (C) UV waves (D) microwaves 26. A signal emitted by an antenna from a certain point can be received at another point of the surface in the form of : (A) Sky wave (B) ground wave (C) sea wave (D) both (A) and (B) 27. The structure of solids is investigated by using. (A) Cosmic (B) X-rays (C) γ-rays (D) infra-red radiations 28. The frequency of electromagnetic wave, which best suited to observe a particle of radius 3 × 10−4 cm is of the order of (A) 1015 (B) 1014 (C) 1013 (D) 1012 29. Which of the following electromagnetic radiations have the longest wavelength ? (A) X-rays (B) γ - rays (C) Microwaves (D) Radiowaves 30. Arrange the following electromagnetic radiations per quantum in the order of increasing energy: (a) Blue light (b) Yellow light (c) X-ray (d) Radiowave The correct choice is : (A) d, b, a, c (B) a, b, d, c (C) c, a, b, d (D) b, a, d, c 31. Microwave oven acts on the principal of (A) giving rotational energy to water molecules (B) giving translational energy to water molecules (C) giving vibrational energy to water molecules (D) Transferring electrons from lower to higher energy levels in water molecule 32. Consider an electromagnetic wave propagating in vacuum. Choose the correct statement. (A) For an electromagnetic wave propagating in +y direction the electric field is E⃗ = 1 √2 Eyz(x,t)zˆ and the magnetic field is B⃗ = 1 √2 Bz(x,t)yˆ (B) For an electromagnetic wave propagating in +y direction the electric fields is E⃗ = 1 √2 Eyz(x,t)yˆ and the magnetic field is B⃗ = 1 √2 Bz(x,t)zˆ (C) For an electromagnetic wave propagating in +x direction the electric field is E⃗ = 1 √2 Eyz(y, z,t)(yˆ + zˆ) and the magnetic field is B⃗ = 1 √2 Byz(y, z,t)(yˆ + zˆ) (D) For an electromagnetic wave propagating in +x direction the electric field is E⃗ = 1 √2 Eyz(x,t)(yˆ − zˆ) and the magnetic field is B⃗ = 1 √2 Byz(x,t)(yˆ + zˆ) 33. An electromagnetic wave travelling in the x- direction has frequency of 2 × 1014 Hz and electric field amplitude of 27Vm−1 . From the options given below, which one describes the magnetic field for this wave? (A) B⃗ (x,t) = (3 × 10−8T)jˆsin [2π(1.5 × 10−8x − 2 × 1014t)] (B) B⃗ (x,t) = (9 × 10−8T)kˆ sin [2π(1.5 × 10−6x − 2 × 1014t)] (C) B⃗ (x,t) = (9 × 10−8 T)iˆsin [2π(1.5 × 10−8x − 2 × 1014t)] (D) None of these 34. For plane electromagnetic wave propagating in the z direction, which one of the following combination gives the correct possible direction for E⃗ and B⃗ field respectively? (A) (iˆ + 2jˆ) and (2iˆ − jˆ) (B) (−2iˆ − 3jˆ) and (3iˆ − 2jˆ) (C) (2iˆ + 3jˆ) and (iˆ + 2jˆ) (D) (3iˆ + 4jˆ) and (4iˆ − 3̂j) INTEGER ANSWER TYPE QUESTIONS The Answers to the following questions are positive integers of 1/2/3 digits or zero. 35. Plane electromagnetic waves of intensity S are incident normally on a flat surface. Only a fraction