PHYSICS

th
12 JEE

ELECTROMAGNETIC
WAVES
 ELECTROMAGNETIC WAVES
DPP-1 (JLP/056)
[Introduction, Ampere’s Circuital Law and its Contradiction,
Maxwell’s Equations, Displacement Current, Sources of
Electromagnetic Waves]
1. The fundamental source of e.m. waves 4. A 100Ω resistance and a capacitor of 100
(A) Is varying magnetic field Ω reactance are connected in series
(B) Is constant magnetic and electric across a 220 V source. When the
fields capacitor is 50% charged, the peak value
(C) Are continuous oscillations of of the displacement current is
electric charge (A) 2.2 A
(D) Is due motion of planets (B) 11 A
(C) 4.4 A
2. Maxwell's equations describe the (D) 11 2A
fundamental laws of
(A) Electricity only 5. The charge on a parallel plate capacitor
(B) Magnetism only varies as q = q0 cos 2t. The plates are
(C) Mechanics only very large and close together (area = A,
(D) Both (A) and (B) separation = d). The displacement current
through the capacitor is
3. According to modified Ampere's circuital (A) q0 2 sint
law (B) –q0 2 sin2t
(iD = displacement current) (C) q0 2 sint
 d E  (D) q0  sin2t
(A)  B  dl  0  iC  0 dt 
6. To establish an instantaneous
dE
(B)  B  dl  0 0 dt
displacement current of I ampere in the
space between the plates of a parallel
(C)  B  dl  0 i 1 dV
plate capacitor of F, the value of
 d E  2 dt
(D)  B  dl  0  iC dt
 iD 
 is nI. Find the value of n.

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7. The velocity of electromagnetic radiation 9. A parallel-plate capacitor having plate
in a medium of permittivity ε0 and area A and plate separation d is joined to
permeability μ0 is given by a battery of emf  and internal resistance
1 0 R at t = 0. Consider a plane surface of
(A) (B) area A/2 parallel to the plates and situated
0 0 0
symmetrically between them. Find the
0 displacement current through this surface
(C) (D) 0 0
0 as a function of time.
 td  td
 0 AR  0 AR
8. The Maxwell’s four equations are written (A) e (B) e
2R R
as  td 2td
q 2 0 AR  0 AR
(C) e (D) e
(i)  E  ds  R 2R
0
(ii)  B  ds  0 10. A parallel plate capacitor of capacitance
d 20 F is being charged by a voltage
(iii)  E  dl   dt  B  ds source whose potential is changing at the
d rate of 3 V/s. The conduction current
(iv)  B  dl  00 dt  E  ds  0 I through the connecting wires, and the
Which of the above Maxwell’s equations displacement current through the plates
shows that electric field lines do not form of the capacitor, would be, respectively
closed loops? (A) Zero, 60 A
(A) (i) Only (B) 60 A, 60 A
(B) (ii) Only (C) 60 A, zero
(C) (iii) Only (D) Zero, zero
(D) (iv) Only

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 DPP-2 (JLP/057)

[Relation Between (Electric Field, Magnetic Field and Speed of

Light), Intensity of Electromagnetic Waves,
Momentum of EM waves, Poynting vector spectrum of EM waves]
1. If oscillation of electric component of 4. A light beam travelling in the x-direction
iˆ  ˆj is described by the electric field Ey = (300
E.M.W is along and that of  x
2 V/m) sin  t   . An electron is
iˆ  ˆj  c
magnetic field is along , the constrained to move along the y-direction
2 with a speed of 2.0  107 m/s. The
direction of propagation of E.M.W is maximum electric force and the
along maximum magnetic force on the electron
(A) iˆ (B)  k̂ are
ˆ
(C) i  jˆ (D) iˆ  ˆj (A) 4.8  10–17 N, zero
(B) 4.2  10–18 N, 1.8  10–8 N
2. An electromagnetic wave is propagating (C) 4.8  10–17 N, 3.2  10–18 N
in vacuum along z-axis, the electric field (D) Zero, zero
component is given by Ex = E0
sin  kz –t  , then magnetic component 5. The electric field intensity produced by
is the radiations coming from 100 W bulb at
E a 3 m distance is E. The electric field
(A) Bx  0 sin  kz – t  intensity produced by the radiations
C
B0 coming from 50 W bulb at the same
(B) By  sin  kz – t  distance is
C
E E
(C) By  0 sin  kz – t  (A)
2
(B) 2E
C
(D) By  B0C sin  kz – t  E
(C) (D) 2E
2
3. An electromagnetic wave with frequency
 and wavelength  travels in the + y 6. The figure shows graphs of the electric
direction. Its magnetic field is along + x-
axis. The vector equation for the field magnitude E versus time t for four
associated electric field (of amplitude E0) uniform electric fields, all contained
is within identical circular regions. Which
 2  of them gives off the magnetic field of
(A) E   E 0 cos  t  y  xˆ highest magnitude?
  
 2 
(B) E  E 0 cos  t  y  xˆ
  
 2 
(C) E  E 0 cos  t  y  zˆ
  
 2  (A) A (B) B
(D) E   E 0 cos  t  y  zˆ (C) C (D) D
  

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7. A radiation of energy ‘E’ falls normally 10. Match List-I (Electromagnetic wave
on a perfectly reflecting surface. The type) with List-II (Its application) and
select the correct option from the choices
momentum transferred to the surface is
given below the list:
(c = Velocity of light)
List-I List-Il
2E (a) Infrared (i) To treat muscular
(A)
c waves strain
2E (b) Radio (ii) For broadcasting
(B)
c2 waves
(c) X-rays (iii) To detect fracture
E
(C) 2 of bones
c
(d) Ultraviolet (iv) Absorbed by the
E ozone layer of the
(D)
c atmosphere
(a) (b) (c) (d)
(A) (iv) (iii) (ii) (i)
8. Which of the following properties is NOT (B) (i) (ii) (iv) (iii)
typically associated with radio waves? (C) (iii) (ii) (i) (iv)
(D) (i) (ii) (iii) (iv)
(A) Long wavelength (1 cm - 100 km)
(B) Low frequency (3 kHz - 300 GHz) 11. Electromagnetic radiation has wavelength
(C) Used in radio communication and 2 nm . To which region of electromagnetic
broadcasting spectrum does it belong?
(A) X-ray region
(D) Highly ionizing (B) Ultra violet region
(C) Infrared region
9. The energy density of electromagnetic (D) Visible region
wave in vacuum is given by the relation
12. X-rays and -rays are both
electromagnetic waves, which one of the
E2 B2 following statements is true?
(A)  (A) In general, X-rays have larger
2 0 2 0
wavelength than that of -rays
1 1 (B) X-rays have smaller wavelength
(B)  0 E 2   0 B2
2 2 than that of -rays
E 2  B2 (C) -rays have smaller frequency than
(C) that of X-rays
c
(D) Wavelength and frequency of X-
1 B2 rays are both larger than those of -
(D) 0 E 2 
2 2 0 rays

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13. Microwaves are commonly used in 15. 5% of the power of 100 W bulb is
heating food because they: converted to visible radiation. Average
(A) Have high energy and can directly intensity of visible radiation at a distance
excite water molecules. 5
of 10 m from the bulb is watt/m2
(B) Are easily absorbed by water and fat 4(n) 2
molecules. Find the value of n.
(C) Penetrate deeply into food without
significant reflection.
(D) All of the above.

14. We consider the radiation emitted by the

human body. Which of the following
statement is true?
(A) The radiation emitted lies in the
ultraviolet region and hence is not
visible
(B) The radiation emitted is in the infra-
red region
(C) The radiation is emitted only during
the day.
(D) The radiation is emitted during the
summers and absorbed during the
winters

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 ANSWER KEY
DPP-01
1. (C) 3. (A) 5. (B) 7. (A) 9. (A)
2. (D) 4. (A) 6. (2) 8. (A) 10. (B)
DPP-02
1. (B) 4. (C) 7. (A) 10. (D) 13. (D)
2. (C) 5. (C) 8. (D) 11. (A) 14. (B)
3. (C) 6. (C) 9. (D) 12. (A) 15. (10)

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