Tag: introduction to electromagnetic waves

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Multiple choice physics observing space: telescopes maxwell's equations the nature of light introduction to electromagnetic waves

Identify which of the following best describe the difference between electromagnetic (EM) waves and other types of waves?

  1. EM waves can travel without a medium.

  2. EM waves are higher in frequency than all other waves

  3. EM waves have shorter wave lengths than any other type of wave.

  4. EM waves transport matter and energy.

  5. EM waves require a medium to travel.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

EM waves do not require a material medium to travel, these can propagate even through vacuum while all other waves require a certain medium to travel.

Multiple choice physics observing space: telescopes maxwell's equations the nature of light introduction to electromagnetic waves

Which of the following is an electromagnetic waves that cause sunburn?

  1. ultraviolet

  2. X-rays

  3. infrared

  4. microwaves

  5. gamma rays
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

UV waves are shorter than visible light waves, so UV possesses more energy than regular light.

UV photons have the right energies to cause chemical changes. When UV light hits your skin, the DNA in your skin cells can undergo chemical change. This chemical change is what sunburn is. In extreme cases, this change in DNA can result in cancer.

Multiple choice physics observing space: telescopes maxwell's equations the nature of light introduction to electromagnetic waves

In an electormagnetic wave, the phase difference between electric field $\vec { E }$ and magnetic field $ \vec { B } $ is :

  1. $\dfrac { \pi }{ 4 } $
  2. $\dfrac { \pi }{ 2 } $
  3. $\pi $

  4. Zero
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The electric and magnetic field components of a linearly polarized electromagnetic wave oscillate in such a way that they peak at the same time and they become zero at the same time but they point to different directions in space, separated by an angle of $90^{\circ}$.


Since there is no time difference between the peaks of the electric and magnetic oscillations the phase difference between the electric and magnetic field vectors of a linearly polarized electromagnetic wave is zero.

Multiple choice physics observing space: telescopes maxwell's equations the nature of light introduction to electromagnetic waves

Electromagnetic wave is deflected by

  1. Electric field

  2. Magnetic field

  3. Both ( 1 ) & ( 2 )

  4. Neither electric field nor magnetic field
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

EM waves are formed by electric and magnetic fields but are not deflected by them, and also they can be deflected by gravitational field....

 Light (electromagnetic wave) has an electric and a magnetic field and should thus deflect a compass needle during daytime.

Visible light - Being an Electromagnetic wave is reflected by glass (take mirror).

For highly intense X-Rays & gamma rays, take that the mirror is stronger such that it could resist for at least 30 seconds.

hence, light wave neither electric field nor magnetic field

Multiple choice physics observing space: telescopes maxwell's equations the nature of light introduction to electromagnetic waves

An electromagnetic wave in vacuum has the electric and magnetic field $\overset { \rightarrow  }{ E } $ and $\overset { \rightarrow  }{ B } $  which are always perpendicular to each other. If the direction of polarization is given by $\overset { \rightarrow  }{ X }  $ and that of wave propagation by $\overset { \rightarrow  }{ k } $ then:

  1. $\overset { \rightarrow }{ X } \parallel \overset { \rightarrow }{ B } $ and $\overset { \rightarrow }{ k } \parallel \overset { \rightarrow }{ B\times } \overset { \rightarrow }{ E } $
  2. $\overset { \rightarrow }{ X } \parallel \overset { \rightarrow }{ E } $ and $\overset { \rightarrow }{ k } \parallel \overset { \rightarrow }{ E\times } \overset { \rightarrow }{ B } $
  3. `$\overset { \rightarrow }{ X } \parallel \overset { \rightarrow }{ B } $ and $\overset { \rightarrow }{ k } \parallel \overset { \rightarrow }{ E\times } \overset { \rightarrow }{ B } $
  4. $\overset { \rightarrow }{ X } \parallel \overset { \rightarrow }{ E } $ and $\overset { \rightarrow }{ k } \parallel \overset { \rightarrow }{ B\times } \overset { \rightarrow }{ E } $
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

In an electromagnetic wave, electrical and magnetic fields are perpendicular to each other. The wave propagates in a direction perpendicular to both electric and magnetic fields as given by  $\vec E\times \vec B$.

So, the direction of propagation of the wave will be perpendicular to the to the direction of oscillation of the fields.
$\overset { \rightarrow }{ k } \parallel \overset { \rightarrow }{ B\times } \overset { \rightarrow }{ E } $
And the direction of polarization must be perpendicular to the electric field and parallel to the magnetic field.
$\vec X||\vec E$.
The correct option is $(B)$.

Multiple choice physics observing space: telescopes maxwell's equations the nature of light introduction to electromagnetic waves

Electro-magnetic wave can be:

  1. Transverse in nature

  2. longitudinal in nature

  3. Both

  4. Electrical in nature
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Electromagnetic waves consist of oscillating electric and magnetic fields that are perpendicular to each other and to the direction of wave propagation. This perpendicular oscillation makes them strictly transverse in nature.

Multiple choice physics observing space: telescopes maxwell's equations the nature of light introduction to electromagnetic waves

The direction of propagation of electromagnetic wave is along.

  1. Electric field vector, $\vec{E}$
  2. Magnetic field vector, $\vec{B}$
  3. $\vec{E}\cdot \vec{B}$
  4. $\vec{E}\times \vec{B}$
  5. $\vec{B}\times \vec{E}$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
The direction of propagation of the electromagnetic wave is always perpendicular to the plane in which $\vec{E}$  and  $\vec{B}$ lies.
So, the direction of the propagation of the wave, $\vec{C}=E\times B$.
So, the correct option is $(D)$
Multiple choice physics observing space: telescopes maxwell's equations the nature of light introduction to electromagnetic waves

The electromagnetic radiations used for taking photographs of objects in dark.

  1. $X$-rays

  2. Infra-red rays
  3. $\gamma$ rays
  4. $UV$ rays
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Answer is B.

Infrared (IR) is invisible radiant energy, electromagnetic radiation with longer wavelengths than those of visible light, extending from the nominal red edge of the visible spectrum at 700 nano-meters to 1 mm. 
Infrared is used in night vision equipment when there is insufficient visible light to see. Night vision devices operate through a process involving the conversion of visible light photons into electrons that are then amplified by a chemical and electrical process and then converted back into visible light. Infrared light sources can be used to enhance the available visible light for conversion by night vision devices, increasing in-the-dark visibility without actually using a visible light source.