How Are Electromagnetic Waves Produced ? What is the Source of the Energy Carried by a Propagating Electromagnetic Wave ? Identify the Electromagnetic Radiations Used (I) in Remote Switches - Physics

Short Note

How are electromagnetic waves produced? What is the source of the energy carried by a propagating electromagnetic wave?
Identify the electromagnetic radiations used
(i) In remote switches of a household electronic device; and
(ii) as a diagnostic tool in medicine



According to Maxwell’s theory accelerated charges radiate electromagnetic waves. Consider a charge oscillating with some frequency. (An oscillating charge is an example of accelerating charge.) This produces an oscillating electric field in space, which produces an oscillating magnetic field, which in turn, is a source of the oscillating electric field, and so on. he oscillating electric and magnetic fields thus regenerate each other, so to speak, as the wave propagates through space. The frequency of the electromagnetic wave naturally equals the frequency of oscillation of the charge. The energy associated with the propagating wave comes at the expense of the energy of the source –the accelerated charge.

The electromagnetic radiation used are :
(1) Infrared rays
(2) X-rays

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2014-2015 (March) Ajmer Set 2

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Arrange the following electromagnetic wave in the order of their increasing wavelength:

(a) γ- rays

(b) Microwaves

(c) X-rays

(d) Radio waves

Do electromagnetic waves carry energy and momentum ?

What is the ratio of the speed of gamma rays to that of radio waves in a vacuum?

How are electric vector `(vec "E")`, magnetic vector `(vec "B")` and velocity vector `(vec "C")` oriented in an electromagnetic wave?

What are the directions of electric and magnetic field vectors relative to each other and relative to the direction of propagation of electromagnetic waves?

Write the following radiations in ascending order with respect to their frequencies:

X-rays, microwaves, UV rays and radio waves.

How does a charge q oscillating at certain frequency produce electromagnetic waves?

Sketch a schematic diagram depicting electric and magnetic fields for an electromagnetic wave propagating along the Z-direction.

In a microwave oven, the food is kept in a plastic container and the microwaves is directed towards the food. The food is cooked without melting or igniting the plastic container. Explain.

Can an electromagnetic wave be deflected by an electric field or a magnetic field?

A capacitor is connected to an alternating-current source. Is there a magnetic field between the plates?

Can an electromagnetic wave be polarised?

A plane electromagnetic wave is passing through a region. Consider (a) electric field (b) magnetic field (c) electrical energy in a small volume and (d) magnetic energy in a small volume. Construct the pairs of the quantities that oscillate with equal frequencies.

An electromagnetic wave going through vacuum is described by
E = E0 sin (kx − ωt); B = B0 sin (kx − ωt).
Which of the following equations is true?

The energy contained in a small volume through which an electromagnetic wave is passing oscillates with

A point charge is moving along a straight line with a constant velocity v. Consider a small area A perpendicular to the motion of the charge. Calculate the displacement current through the area when its distance from the charge is x. The value of x is not large, so that the electric field at any instant is essentially given by Coulomb's law.

A laser beam has intensity 2.5 × 1014 W m−2. Find amplitudes of electric and magnetic fields in the beam.

The energy associated with light of which of the following colours is minimum : 

This is an example of step-up transformer .

Define frequency modulation and state any one advantage of frequency modulation (FM) over amplitude modulation (AM). 

State any one property which is common to all electromagnetic waves.

The energy levels of an atom of a certain element are shown in the given figure. Which one of the transitions A, B, C, D or E will result in the emission of photons of electromagnetic radiation of wavelength 618.75 nm? Support your answer with mathematical calculations.

The electric and magnetic fields, associated with an electromagnetic wave, propagating along negative X-axis can be represented by ______.

An e.m. wave is propagating in a medium with a velocity `vec"v" = "v" hat"i"`. The instantaneous oscillating electric field of this e.m. wave is along +y-axis, then the direction of an oscillating magnetic field of the e.m. wave will be along:

If the magnetic monopole exists, then which of the Maxwell’s equation to be modified?

Fraunhofer lines are an example of _______ spectrum.

Let E = E0 sin[106 x -ωt] be the electric field of plane electromagnetic wave, the value of ω is ______.

Give two uses of IR radiation.

Give two uses of UV radiation.

Write a short note on the X-ray.

Write a short note on the visible spectrum.

Explain the importance of Maxwell’s correction.

Which of these mechanisms can be used to produce electromagnetic waves?

Velocity of plane electromagnetic waves in vacuum equals ______.

A man standing on the road has to hold his umbrella at 30° with the vertical to keep the rain away. He throws away the umbrella and starts, running at 10 km/h and finds raindrops hitting his head vertically. The speed of the raindrops with respect to the road is ______.

In space communication, the sound waves can be sent from one place to another

A plane electromagnetic wave travels in free space along x-axis. At a particular point in space, the electric field along y-axis is 9.3 Vm−1. The magnetic induction (B) along z-axis is:

Dimensions of 1/(µOE0) is

Which of the following electromagnetic radiations has the smallest wave length?

The velocity of electromagnetic wave is parallel to

Which of the following are not electromagnetic waves?

The sun delivers 103w/m2 of electromagnetic flux to the earth's surface. The total power that is incident on a roof of dimension 8m/10m will be

Dimensions of ε0 `(d phi_ε)/(dt)` are of

For which frequency of light, the eye is most sensitive?

Electromagnetic waves are produced by ______.

Which of the following type of radiations are radiated by an oscillating electric charge?

For a plane electromagnetic wave propagating in x-direction, which one of the following combinations gives the correct possible directions for electric field (E) and magnetic field (B) respectively?

For a plane electromagnetic wave propagating in the x-direction, which one of the following combinations gives the correct possible directions for the electric field (E) and magnetic field (B) respectively?

An EM wave radiates outwards from a dipole antenna, with E0 as the amplitude of its electric field vector. The electric field E0 which transports significant energy from the source falls off as ______.

An electromagnetic wave travels in vacuum along z direction: `E = ( E_1hati + E_2hatj ) cos (kz - ωt)`. Choose the correct options from the following:

  1. The associated magnetic field is given as `B = 1/c(E_1hati - E_2hatj) cos (kz - ωt)`.
  2. The associated magnetic field is given as `B = 1/c(E_1hati - E_2hatj) sin (kz - ωt)`.
  3. The given electromagnetic field is circularly polarised.
  4. The given electromagnetic wave is plane polarised.

An infinitely long thin wire carrying a uniform linear static charge density λ is placed along the z-axis (figure). The wire is set into motion along its length with a uniform velocity `v = vhatk_z`. Calculate the poynting vector `S = 1/mu_0 (E xx B)`.

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 ε0 = 8.85 × 10–12 C2 N–1 – m–2, speed of light in vacuum c = 3 × 108 ms-1)

A plane electromagnetic wave of frequency 500 MHz is travelling in a vacuum along a y-direction.

At a particular point in space and time, `vec"B"` = 8.0 × 10-8 `hat"Z"`T. The value of the electric field at this point is ______.

(speed of light = 3 × 108 ms-1)

`hat x, hat y, hat z` are unit vectors along x, y, and Z directions.

A plane electromagnetic wave, has frequency of 2.0 × 1010 Hz and its energy density is 1.02 × 10-8 J/m3 in vacuum. The amplitude of the magnetic field of the wave is close to `(1/(4piepsilon_0) = 9xx10^9"Nm"^2/"C"^2  "and speed of light" = 3 xx 10^8  "m"  "s"^-1)`:

The electric field in a plane electromagnetic wave is given by `vecE = 200cos[((0.5 xx 10^3)/m)x - (1.5 xx 10^11 "rad"/s xx t)]V/mhatj`. If the wave falls normally on a perfectly reflecting surface having an area of 100 cm2. If the radiation pressure exerted by the E.M. wave on the surface during a 10-minute exposure is `x/10^9 N/m^2`. Find the value of x.

Sunlight falls normally on a surface of area 36 cm2 and exerts an average force of 7.2 × 10-9 N within a time period of 20 minutes. Considering a case of complete absorption the energy flux of incident light is ______.

The electric field in an electromagnetic wave is given by E = 56.5 sin ω(t - x/c)Nc-1. Find the intensity of the wave if it is propagating along x-axis in the free space.

(Given ε0 = 8.85 × 10-12 C2 N-1 m-2)

A plane electromagnetic wave with frequency of 30 MHz travels in free space. At particular point in space and time, electric field is 6 V/m. The magnetic field at this point will be x × 10-8 T. The value of x is ______.

In a plane electromagnetic wave, the direction of electric field and magnetic field are represented by `hat"k"` and 2`hat"i" - 2hat"j"`, respectively. What is the unit vector along direction of propagation of the wave.

A 27 mW laser beam has a cross-sectional area of 10 mm2. The magnitude of the maximum electric field in this electromagnetic wave is given by:

[Given permittivity of space ∈0 = 9 × 10-12 SI units, Speed of light c = 3  108 m/s] 

An electromagnetic wave of frequency v = 3.0 MHz passes from vacuum into a dielectric medium with permittivity ∈ = 4.0. Then ______.

Name the electromagnetic wave/radiation which is used to study crystal structure.


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