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1 Electromagnetic Waves Properties. The electric and the magnetic field, associated with an electromagnetic wave, propagating along the z=axis. Can be represented by E = E kˆ, = iˆ E = E ˆj, = ˆj b) E = E ˆ, ˆ j = K d) E = E ˆ, ˆ j = J. The electromagnetic wave having the shortest wavelength is X-rays b) γ -rays Infrared rays d) Microwaves 3. The part of the spectrum of the electromagnetic radiation used to cook food is Ultraviolet rays b) Cosmic rays X-rays d) Microwaves 4. A part of the spectrum of the electromagnetic radiation used to cook food is Ultraviolet rays b) Cosmic rays Elliptical d) Planar 5. For a medium with permittivity ε and permeability µ, the velocity of light is given by µ / g b) µε / µε d) ε / µ 6. An electromagnetic wave going through vacuum is described by E = E sin( kx ωt), = sin( kc ωt). Which of the following equations is true? E k = ω b) E ω = k E = ωk d) None of these 7. A source emits electromagnetic waves of wavelength 3m. One beam reaches the observer directly and other after reflection from a water surface, travelling.5m extra distance and with intensity reduced to (/4) as compared to intensity due to direct beam alone. The resultant intensity will be (/4) fold b) (3/4) fold (5/4) fold d) (9/4) fold 8. The essential distinction between X-rays and γ rays is that γ -rays have smaller wavelength than X-rays b) γ -rays emanate from nucleus while x-rays emanate from outer part of the atom γ -rays have greater ionizing power than X-rays d) γ -rays are more penetrating than x-rays

2 9. The spped of electromagnetic wave in vacuum depends upon the source of radiation Increases as we move from γ -rays to radio waves b) Decreases as we move from γ -rays to radio waves Is same for all of them d) None of the above. In free space electron is placed in the path of a plane electromagnetic wave, it will start moving along Centre of Earth b) Equator of Earth Magnetic Field d) Electric Field. The average magnetic energy density of an electromagnetic wave length λ travelling in free space is given by λ µ λ b) d) µ µ λ. The magnetic field in a plane electromagnetic wave is given by ( ) 7 3 = sin.5 x +.5 t y This electromagnetic wave is A visible light b) An infrared wave A microwave d) A radio wave 3. Which of the following shows green house effect? Ultraviolet rays b) Infrared rays X-rays d) None of these 4. A plane electromagnetic wave propagating in the X-direction has wavelength of 6. mm. The electric field is in the Y-direction and its maximum magnitude of 33Vm. The equation for the electric field as function of x and t is sin π ( t x / b) 33sinπ ( t x / 33sin π ( t x / d) sinπ ( t x / 5. Which of the following statement is false for the properties of electromagnetic waves? oth electric and magnetic field vectors attain the maxima and minima at the same place and same time. b) The energy is electromagnetic wave is divided equally between electric and magnetic vectors. oth 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.

3 6. Which one of the following is the property of monochromatic, plane electromagnetic waves in free space? Electric and magnetic fields have a phase difference of π /. b) The energy contribution of both electric and magnetic fields are equal. The direction of propagation is in the direction of x E. d) The pressure exerted by the wave is the product of its speed and energy density. e) The speed of the wave is /e. 7. Which of the following waves has the maxi wavelength? X-rays b) IR rays UV rays d) Radiowaves 4 8. The sun delivers W / m of electromagnetic flux the earth s surface. The total power that is incident roof of dimensions ( ) 4 W b) W 6 W d) W 5 7 m will be 9. Velocity of electromagnetic waves in vacuum is given by µ µ ε b) ε ε µ d) µ ε. Which is the correct expression of velocity of light? c µ ε µ E b) d) All of these. Which force in nature exists every where? 9 Nuclear force b) Electromagnetic force Weak force d) Gravitation. The average electric field of electromagnetic waves in certain region of free space 4 is9 NC. Then the average magnetic field in the same region is of the order of 4 7 T b) 3 T 3 4 T d) 3 T e) 3 T

4 3. If ε and µ are respectively, the electric permittivity and the magnetic permeability of free space, ε and µ the corresponding quantities in a medium, the refractive index of the medium is µε µ ε b) µε µ ε µ ε µε d) µµ εε 4. Which of the following has/have zero average value in a plane electromagnetic wave? oth magnetic and electric fields b) Electric field only Magnetic field only d) Magnetic energy e) Electric energy 5. An electromagnetic wave has Electric vector only b) Magnetic vector only Electric and magnetic vectors perpendicular to each other d) Neither the electric vector nor the magnetic vector 6. In fog, neither photographs vector nor the magnetic vector radiations are more clear than those obtained during visible light because Scattering of I-R light is more than visible light b) Scattering of I-R light is more than visible light The intensity of I-R light from the object is less d) Scattering of I-R light is less than visible light 7. The velocity of an electromagnetic wave in vacuum can be changed by changing 8 Frequency b) Amplitude Wavelength 4) None of these 8. The velocity of electromagnetic radiation in a medium of permittivityε and permeability µ is given by ε µ b) µ ε µ ε µ d) ε

5 9. Assertion (A): Displacement current goes through the gap between the plates of a capacitor when the charge of the capacitor does not change. Reason (R): The displacement current arises in the region in which the electric field and hence the electric flux does not change with time. oth A and R are true and R is the correct explanation of A. b) oth A and R are true and R is not correct explanation of A. A is true but R is false. d) A is false but R is true. 3. In an electromagnetic wave, the electric and magnetising fields are.55 Am. The maximum energy flow is 6.5Wm b) 46.7Wm d) 36.5Wm 765 Wm Vm 3. In an oscillating L-C circuit the maximum charge on the capacitor is Q. The charge on 7 the capacitor when the energy is stored equally between the electric and magnetic fields is Q/ b) Q / 3 Q / d) Q 3. The electric and magnetic fields of an electromagnetic wave are In phase and parallel to each other b) In opposite phase and perpendicular to each other In opposite phase and parallel to each other d) In phase and perpendicular to each other 33. Electromagnetic waves are produced by Accelerated charged particle b) Decelerated charged particle Charge in uniform motion d) None of the above 34. A beam of light travelling along x-axis is described by the electric field E ( 6Vm ) sin ω ( t x / y moving along y-axis with a speed of 7 9. N b).9 N. Then maximum magnetic force on a charge q=e, ms.9 N d) None of the above 9 is ( e =.6 C) and

6 35. The sound waves after being converted into electrical waves are not transmitted as such because They are heavily absorbed by the atmosphere b) They travelled with the speed of sound The height of antenna has to be increased several times d) The frequency is not constant 36. All components of the electromagnetic spectrum in vacuum have the same 6 Energy b) Velocity C) Wavelength D) Frequency 37. The electric field E and magnetic field in electromagnetic wave are Parallel to each other b) Inclined at an angle of Perpendicular to each other 4) Opposite to each other 38. The magnetic field amplitude of an electromagnetic wave is amplitude if the wave is travelling in free space is 6Vm b) 6Vm / 6Vm d) None of these 45 7 T. It electric field 39. A perfectly reflecting mirror has an area ofcm. Light energy is allowed to fall on it for h at the rate ofw cm. The force that acts on the mirror is b) 6.7 N N d).4 N 4. A parallel plate capacitor is charged to 6µ C. Due to a radioactive source, the plate 8 loses charge at the rate of.8 Cs. The magnitude of displacement current is Cs b) 3.6 Cs 4. Cs d) 5.7 Cs

7 Electromagnetic Waves Properties Key ) d ) b 3) a 4) a 5) b 6) a 7) d 8) b 9) c ) d ) b ) c 3) b 4) b 5) c 6) b 7) d 8) c 9) d ) d ) b ) b 3) a 4) a 5) c 6) d 7) d 8) c 9) d 3) a 3) c 3) d 33) a 34) b 35) a 36) b 37) c 38) b 39) b 4) a E 6. c = π k = and ω = π v λ E k = ω 3 7. Resultant amplitude = I + I / 4 = I. Resultant intensity U = εe + µ µ Solutions = I = I = fold y = sin (.5 x = 5 t) Comparing with, = ( kx + ωt) 3 k =.5 π.5 λ = 3 y.56 sin The wavelength range of microwaves is to.3. The wavelength of this wave lies 3

8 4. 3 between to.3, Hence the equation represents a microwaves. π c π 3 ω = π v = = 3 λ 6 x Ey = E sinω t = 33sinπ t x / c c 8 ( ) 4 6 = = W 8. Total power = solar constant x area ( ) 3. S = E H =, =.65 E Vm H Am 3. U E max U S =.6 = 6.5Wm R max Q = C Li = Where I is the current at this time, for the given instant U E = U q Li C = From energy conservation U + U = U = U E 34. = c E E max max q Q Q = q = C C 8 E = 6 Vm, c = 3 ms 6 = = 3 8 F = qv = ev m 6 T = E = E in( kx ωt) and = ( kx ωt) c E = or E = c 7 8 = T, c = 3 ms sin 7 8 E = 3 = 6Tm = 6Vm 7 =.9 N

9 h h hv E p = = = = λ c v c c ( / ) On reflection, change in momentum per second = force E = p = c I d dq = =.8 dt = = Cs 8 N Electromagnetic Spectrum. Refractive index of the material of a prism is.5. If δ m = A what will be a value of angle of the given prism? (where δ m =minimum deviation and A=angle of prism) 8.8 b) d) 9. The rate of loss of heat of a body is directly proportion to the difference of temperature of the body and surroundings. This statement is known as Stefan s law b) Newton s law of cooling Wien s law d) Kirchhoff s law 3. The maximum kinetic energy of photoelectrons Various linearly with the frequency of the incident radiation b) Various linearly with the wavelength of incident light Proportional to the frequency of the incident radiation d) Proportional to the square of the frequency of incident radiation 8 4. Which of the following undergoes largest diffraction? Infrared light b) Radio waves γ -rays d) Ultraviolet light

10 7 5. An electromagnetic radiation has energy of 3. kev. Then the radiation belongs to the region of Visible Light b) Ultraviolet Infrared d) X-ray e) Microwave 6 6. The correct option, if speed of gamma rays, X-rays and microwaves are v, v and v respectively will be v > v > v b) vg < vx < vm g x m v > v < v d) vg = vx = vm g x m g x m 7. We find that the temperature of air decreases as one goes up from the earth s surface because The atmospheric pressure drops with height b) The earth which radiates in the infrared region is the main heat source and temperature drops a we go away from it. The density of air drops with height and the air therefore cannot hold stronger as we go up d) Winds are stronger as we go up 8. The wavelength of a radio wave of frequency of MHz is 4 m b) 3m 35 m d) m 5 9. In the electromagnetic spectrum, the visible spectrum lies between Radio Wave and Microwaves b) Infrared and Ultraviolet Rays Microwaves and Infrared Spectrum d) X-ray and Gamma Ray Spectrum 4. Which radiations are used in treatment of muscles ache? Infrared b) Ultraviolet Microwave d) X-rays. The waves which cannot travel in vacuum are X-Rays b) Radio Waves Infrasonic Waves d) Ultraviolet Rays

11 . A fire screen produces sensation of cooling as It allows both infrared and visible light but cuts off ultraviolet b) It allows infrared and cuts off shorter wavelengths It cuts off both visible light and infrared d) It allows only visible light and cuts off infrared Electromagnetic Spectrum Key )a )b 3)a 4)b 5)d 6)d 7)b 8)b 9)b )a )c )d. µ =.5 and δ m = A 5. hc E = λ A + δm sin µ = A sin A + A sin sin A.5 = = A A sin sin A= 8.8 Solutions Or λ = hc E = =.9375 m (Wavelength range of X-rays is from 8 mto m to A) 8. 8 c 3 λ = = = 3 = 3m 6 v

MCQs E M WAVES. Physics Without Fear.

MCQs E M WAVES. Physics Without Fear. MCQs E M WAVES Physics Without Fear Electromagnetic Waves At A Glance Ampere s law B. dl = μ 0 I relates magnetic fields due to current sources. Maxwell argued that this law is incomplete as it does not