Sign in
12thPass logo
New chatPYQ LibraryDoubtsRank report
Sign in to see Recents

Your guest activity stays on this device

Sign in to save progress →
Sign in

Electromagnetic Waves question

2020 · 4 Sep · Shift 2 · Q54
Guest · filters and generic practice availableBrowsing as a guest · PYQ filters and generic practice are available. Sign in only for personalised features and saved progress.
  1. PYQ Library
  2. /JEE Main
  3. /Physics
  4. /Electromagnetic Waves
  5. /2020 · 4 Sep · Shift 2 · Q54

Electromagnetic Waves question

2020 · 4 Sep · Shift 2 · Q54

JEE MainPhysicsElectromagnetic WavesMCQ+4 / −1
The electric field of a plane electromagnetic wave is given by E→=E0(x^+y^)sin⁡(kz−ωt)\overrightarrow E = {E_0}\left( {\widehat x + \widehat y} \right)\sin \left( {kz - \omega t} \right)E=E0​(x+y​)sin(kz−ωt) Its magnetic field will be given by :
  1. A
    E0c(x^+y^)sin⁡(kz−ωt){{{E_0}} \over c}\left( {\widehat x + \widehat y} \right)\sin \left( {kz - \omega t} \right)cE0​​(x+y​)sin(kz−ωt)
  2. B
    E0c(x^−y^)sin⁡(kz−ωt){{{E_0}} \over c}\left( {\widehat x - \widehat y} \right)\sin \left( {kz - \omega t} \right)cE0​​(x−y​)sin(kz−ωt)
  3. C
    E0c(x^−y^)cos⁡(kz−ωt){{{E_0}} \over c}\left( {\widehat x - \widehat y} \right)\cos \left( {kz - \omega t} \right)cE0​​(x−y​)cos(kz−ωt)
  4. D
    E0c(−x^+y^)sin⁡(kz−ωt){{{E_0}} \over c}\left( { - \widehat x + \widehat y} \right)\sin \left( {kz - \omega t} \right)cE0​​(−x+y​)sin(kz−ωt)
View written solutionFree

Correct answer: D

  1. Given electric field

    E⃗=E0(x^+y^)sin⁡(kz−ωt)\vec E = E_0(\hat x+\hat y)\sin(kz-\omega t)E=E0​(x^+y^​)sin(kz−ωt)

    Since the phase is kz−ωtkz-\omega tkz−ωt, the wave propagates in the +z+z+z direction.

  2. Relation between E⃗\vec EE, B⃗\vec BB, and direction of propagation

    For a plane electromagnetic wave in vacuum,

    B⃗=1c n^×E⃗\vec B = \frac{1}{c}\,\hat n \times \vec EB=c1​n^×E

    where n^\hat nn^ is the unit vector in the direction of propagation.

    Here,

    n^=z^\hat n = \hat zn^=z^

    so

    B⃗=1cz^×E⃗\vec B = \frac{1}{c}\hat z \times \vec EB=c1​z^×E

  3. Compute the cross product

    Substitute E⃗\vec EE:

    B⃗=E0c[z^×(x^+y^)]sin⁡(kz−ωt)\vec B = \frac{E_0}{c}\left[\hat z \times (\hat x+\hat y)\right]\sin(kz-\omega t)B=cE0​​[z^×(x^+y^​)]sin(kz−ωt)

    Using

    z^×x^=y^,z^×y^=−x^\hat z\times \hat x = \hat y, \qquad \hat z\times \hat y = -\hat xz^×x^=y^​,z^×y^​=−x^

    therefore,

    z^×(x^+y^)=y^−x^=−x^+y^\hat z\times (\hat x+\hat y)=\hat y-\hat x=-\hat x+\hat yz^×(x^+y^​)=y^​−x^=−x^+y^​

    Hence,

    B⃗=E0c(−x^+y^)sin⁡(kz−ωt)\vec B = \frac{E_0}{c}(-\hat x+\hat y)\sin(kz-\omega t)B=cE0​​(−x^+y^​)sin(kz−ωt)

  4. Match with options

    This corresponds to Option D.

  5. Check with stored answer

    Stored correct answer: D

    Derived answer: D

    They match.

PreviousNext

More from Electromagnetic Waves

  • An electron is constrained to move along the y-axis with a speed of 0.1 c (c is the speed of light) in the presence of electromagnetic wave, whose electric field is E=30j​sin(1.5×107t−5×10−2x)…2020 · MCQ
  • The correct match between the entries in column I and column II are : Includes table2020 · MCQ
  • Suppose that intensity of a laser is π315​ W/m2. The rms electric field, in units of V/m associated with this source is close to the nearest integer is ​. ∈ 0 = 8.86 × 10–12 C2 Nm–2; c = 3 × 108…2020 · Numerical
  • For a plane electromagnetic wave, the magnetic field at a point x and time t is B(x,t)=[1.2×10−7sin(0.5×103x+1.5×1011t)k]…2020 · MCQ
  • If the magnetic field in a plane electromagnetic wave is given by B= 3 × 10-8 sin(1.6 × 103x + 48 × 1010t) j​ T, then what will be expression for electric field ?2020 · MCQ
  • The electric field of a plane electromagnetic wave is given by E=E0​2​i+j​​cos(kz+ωt) At t = 0, a positively charged particle is at the point (x, y, z) =(0,0,kπ​)…2020 · MCQ
  • A plane electromagnetic wave of frequency 25 GHz is propagating in vacuum along the z-direction. At a particular point in space and time, the magnetic field is given by B=5×10−8j​T. The…2020 · MCQ
  • The electric fields of two plane electromagnetic plane waves in vacuum are given by E1​​=E0​j​cos(ωt−kx) and E2​​=E0​kcos(ωt−ky)…2020 · MCQ