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

2022 · 28 Jun · Shift 1 · Q53
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. /2022 · 28 Jun · Shift 1 · Q53

Electromagnetic Waves question

2022 · 28 Jun · Shift 1 · Q53

JEE MainPhysicsElectromagnetic WavesMCQ+4 / −1
A radar sends an electromagnetic signal of electric field (E0) = 2.25 V/m and magnetic field (B0) = 1.5 ×\times× 10 −-− 8 T which strikes a target on line of sight at a distance of 3 km in a medium. After that, a part of signal (echo) reflects back towards the radar with same velocity and by same path. If the signal was transmitted at time t = 0 from radar, then after how much time echo will reach to the radar?
  1. A
    2.0 ×\times× 10 −-− 5 s
  2. B
    4.0 ×\times× 10 −-− 5 s
  3. C
    1.0 ×\times× 10 −-− 5 s
  4. D
    8.0 ×\times× 10 −-− 5 s
View written solutionFree

Correct answer: B

  1. Use the relation between electric and magnetic fields of an electromagnetic wave

For an electromagnetic wave in a medium,

v=E0B0v = \frac{E_0}{B_0}v=B0​E0​​

Given:

E0=2.25 V/mE_0 = 2.25\ \text{V/m}E0​=2.25 V/m B0=1.5×10−8 TB_0 = 1.5 \times 10^{-8}\ \text{T}B0​=1.5×10−8 T

So,

v=2.251.5×10−8=1.5×108 m/sv = \frac{2.25}{1.5 \times 10^{-8}} = 1.5 \times 10^8\ \text{m/s}v=1.5×10−82.25​=1.5×108 m/s

  1. Find the total distance traveled by the radar signal

The target is at a distance of 3 km3\ \text{km}3 km from the radar.

One-way distance:

d=3 km=3000 md = 3\ \text{km} = 3000\ \text{m}d=3 km=3000 m

Since the signal goes to the target and the echo returns back by the same path, total distance is:

D=2d=2×3000=6000 mD = 2d = 2 \times 3000 = 6000\ \text{m}D=2d=2×3000=6000 m

  1. Calculate the total time for the echo to return

t=Dv=60001.5×108t = \frac{D}{v} = \frac{6000}{1.5 \times 10^8}t=vD​=1.5×1086000​

t=4.0×10−5 st = 4.0 \times 10^{-5}\ \text{s}t=4.0×10−5 s

  1. Match with the options

4.0×10−5 s4.0 \times 10^{-5}\ \text{s}4.0×10−5 s

This corresponds to Option B.

PreviousNext

More from Electromagnetic Waves

  • An EM wave propagating in x-direction has a wavelength of 8 mm. The electric field vibrating y-direction has maximum magnitude of 60 Vm − 1. Choose the correct equations for electric and magnetic fields if the EM wave is propagating in…2022 · MCQ
  • Match List - I with List - II : Choose the correct answer from the options given below : Includes table2022 · MCQ
  • Nearly 10% of the power of a 110 W light bulb is converted to visible radiation. The change in average intensities of visible radiation, at a distance of 1 m from the bulb to a distance of 5 m is a×10−2 W/m2…2022 · Numerical
  • The intensity of the light from a bulb incident on a surface is 0.22 W/m2. The amplitude of the magnetic field in this light-wave is ​× 10 − 9 T. (Given : Permittivity of vacuum ∈ 0 = 8.85 × 10…2022 · Numerical
  • The displacement current of 4.425 μ A is developed in the space between the plates of parallel plate capacitor when voltage is changing at a rate of 106 Vs − 1. The area of each plate of the capacitor is 40 cm2. The distance between…2022 · Numerical
  • An expression for oscillating electric field in a plane electromagnetic wave is given as Ez = 300 sin(5 π× 103x − 3 π× 1011t) Vm − 1 Then, the value of magnetic field amplitude will be : (Given : speed of light in…2022 · MCQ
  • Electric field of plane electromagnetic wave propagating through a non-magnetic medium is given by E = 20cos(2 × 1010 t − 200x) V/m. The dielectric constant of the medium is equal to : (Take μ r = 1)2021 · MCQ
  • A plane electromagnetic wave of frequency 500 MHz is travelling in vacuum along y-direction. At a particular point in space and time, B= 8.0 × 10 − 8 z T. The value of electric field at this point is :…2021 · MCQ