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

2021 · 22 Jul · Shift 2 · Q52
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. /2021 · 22 Jul · Shift 2 · Q52

Electromagnetic Waves question

2021 · 22 Jul · Shift 2 · Q52

JEE MainPhysicsElectromagnetic WavesMCQ+4 / −1
Intensity of sunlight is observed as 0.092 Wm −-− 2 at a point in free space. What will be the peak value of magnetic field at the point? (ε0=8.85×10−12C2N−1m−2{\varepsilon _0} = 8.85 \times {10^{ - 12}}{C^2}{N^{ - 1}}{m^{ - 2}}ε0​=8.85×10−12C2N−1m−2)
  1. A
    2.77 ×\times× 10 −-− 8 T
  2. B
    1.96 ×\times× 10 −-− 8 T
  3. C
    8.31 T
  4. D
    5.88 T
View written solutionFree

Correct answer: A

  1. Use the relation between intensity and field amplitudes

For an electromagnetic wave in free space, the average intensity is

I=12cε0E02I=\frac{1}{2}c\varepsilon_0 E_0^2I=21​cε0​E02​

Also, since

E0=cB0,E_0=cB_0,E0​=cB0​,

we can write

=\frac{1}{2}\varepsilon_0 c^3 B_0^2$$ So, $$B_0=\sqrt{\frac{2I}{\varepsilon_0 c^3}}$$ --- 2. **Substitute the given values** Given: $$I=0.092\ \text{W m}^{-2}$$ $$\varepsilon_0=8.85\times 10^{-12}$$ $$c=3\times 10^8\ \text{m s}^{-1}$$ Thus, $$B_0=\sqrt{\frac{2\times 0.092}{(8.85\times 10^{-12})(3\times 10^8)^3}}$$ --- 3. **Compute the denominator** First, $$(3\times 10^8)^3=27\times 10^{24}=2.7\times 10^{25}$$ Now, $$\varepsilon_0 c^3=(8.85\times 10^{-12})(2.7\times 10^{25})$$ $$=23.895\times 10^{13}=2.3895\times 10^{14}$$ --- 4. **Compute the fraction** Numerator: $$2I=0.184$$ Therefore, $$B_0^2=\frac{0.184}{2.3895\times 10^{14}}\approx 7.70\times 10^{-16}$$ So, $$B_0=\sqrt{7.70\times 10^{-16}}\approx 2.77\times 10^{-8}\ \text{T}$$ --- 5. **Match with the options** $$B_0\approx 2.77\times 10^{-8}\ \text{T}$$ So the correct option is: **A: $2.77\times 10^{-8}\ \text{T}$** --- 6. **Comparison with stored answer** Stored correct answer: **A** Our derived answer: **A** They match.
PreviousNext

More from Electromagnetic Waves

  • An electromagnetic wave of frequency 5 GHz, is travelling in a medium whose relative electric permittivity and relative magnetic permeability both are 2. Its velocity in this medium is ​× 107 m/s.2021 · Numerical
  • Match List - I with List - II. Choose the correct answer from the options given below : Includes table2021 · MCQ
  • An electromagnetic wave of frequency 3 GHz enters a dielectric medium of relative electric permittivity 2.25 from vacuum. The wavelength of this wave in that medium will be ​× 10 − 2 cm.2021 · Numerical
  • The peak electric field produced by the radiation coming from the 8W bulb at a distance of 10 m is 10x​πμ0​c​​mV​. The efficiency of the bulb is 10% and it is a point source. The value of x…2021 · Numerical
  • The wavelength of an X-ray beam is 10 Ao​. The mass of a fictitious particle having the same energy as that of the X-ray photons is 3x​h kg. The value of x is ​. (h = Planck's constant)2021 · Numerical
  • A linearly polarized electromagnetic wave in vacuum is E=3.1cos[(1.8)z−(5.4×106)t]iN/C is incident normally on a perfectly reflecting wall at z = a. Choose the correct option2021 · MCQ
  • The electric field in a plane electromagnetic wave is given by E=200cos[(m0.5×103​)x−(1.5×1011srad​×t)]mV​j​…2021 · Numerical
  • A light beam is described by E=800sinω(t−cx​). An electron is allowed to move normal to the propagation of light beam with a speed of 3 × 107 ms − 1. What is the maximum magnetic force…2021 · MCQ