Tag: the nature of light

Questions Related to the nature of light

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

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

  1. ultraviolet

  2. X-rays

  3. infrared

  4. microwaves

  5. gamma rays

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Correct Option: A
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.

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

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

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

  2. $\dfrac { \pi }{ 2 } $

  3. $\pi $

  4. Zero

Show answer
Correct Option: D
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.

Electromagnetic wave is deflected by

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

  1. Electric field

  2. Magnetic field

  3. Both ( 1 ) & ( 2 )

  4. Neither electric field nor magnetic field

Show answer
Correct Option: D
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

Wavelength of an electron having energy 10KeV is ...........$ A^0 $

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

  1. 0.12

  2. 1.2

  3. 12

  4. 120

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Correct Option: C

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:

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

  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 } $

Show answer
Correct Option: C
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 $(B)$.

Electro-magnetic wave can be:

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

  1. Transverse in nature

  2. longitudinal in nature

  3. Both

  4. Electrical in nature

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Correct Option: C

Intensity of electromagnetic wave will be

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

  1. $I=c{\mu} _{0}{B} _{0}^{2}/2$

  2. $I=c{\epsilon} _{0}{B} _{0}^{2}/2$

  3. $I={B} _{0}^{2}/c{\mu} _{0}$

  4. $I={E} _{0}^{2}/c{\epsilon} _{0}$

Show answer
Correct Option: B

The direction of propagation of electromagnetic wave is along.

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

  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. $\vec{B}\times \vec{E}$

Show answer
Correct Option: D
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 $(D)$

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

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

  1. $X$-rays

  2. Infra-red rays

  3. $\gamma$ rays

  4. $UV$ rays

Show answer
Correct Option: B
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.

Light appears to travel in a straight line, because.

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

  1. Its wavelength is very small

  2. Its velocity is large

  3. It is not absorbed by surroundings

  4. It is reflected by surroundings

Show answer
Correct Option: A
Explanation:

Light appears to travel in a straight line because diffraction (or deviation from the path) is least in light. Diffraction is least because -of small wavelength of light. So small wave length of light causes the light to travel almost in straight line.